ext4: dirty page has always buffers attached

[pandora-kernel.git] / fs / ext4 / inode.c

/*
 *  linux/fs/ext4/inode.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card (card@masi.ibp.fr)
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  from
 *
 *  linux/fs/minix/inode.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  64-bit file support on 64-bit platforms by Jakub Jelinek
 *      (jj@sunsite.ms.mff.cuni.cz)
 *
 *  Assorted race fixes, rewrite of ext4_get_block() by Al Viro, 2000
 */

#include <linux/fs.h>
#include <linux/time.h>
#include <linux/jbd2.h>
#include <linux/highuid.h>
#include <linux/pagemap.h>
#include <linux/quotaops.h>
#include <linux/string.h>
#include <linux/buffer_head.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include <linux/mpage.h>
#include <linux/namei.h>
#include <linux/uio.h>
#include <linux/bio.h>
#include <linux/workqueue.h>
#include <linux/kernel.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>

#include "ext4_jbd2.h"
#include "xattr.h"
#include "acl.h"
#include "truncate.h"

#include <trace/events/ext4.h>

#define MPAGE_DA_EXTENT_TAIL 0x01

static __u32 ext4_inode_csum(struct inode *inode, struct ext4_inode *raw,
                              struct ext4_inode_info *ei)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        __u16 csum_lo;
        __u16 csum_hi = 0;
        __u32 csum;

        csum_lo = raw->i_checksum_lo;
        raw->i_checksum_lo = 0;
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
            EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi)) {
                csum_hi = raw->i_checksum_hi;
                raw->i_checksum_hi = 0;
        }

        csum = ext4_chksum(sbi, ei->i_csum_seed, (__u8 *)raw,
                           EXT4_INODE_SIZE(inode->i_sb));

        raw->i_checksum_lo = csum_lo;
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
            EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi))
                raw->i_checksum_hi = csum_hi;

        return csum;
}

static int ext4_inode_csum_verify(struct inode *inode, struct ext4_inode *raw,
                                  struct ext4_inode_info *ei)
{
        __u32 provided, calculated;

        if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
            cpu_to_le32(EXT4_OS_LINUX) ||
            !EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
                EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
                return 1;

        provided = le16_to_cpu(raw->i_checksum_lo);
        calculated = ext4_inode_csum(inode, raw, ei);
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
            EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi))
                provided |= ((__u32)le16_to_cpu(raw->i_checksum_hi)) << 16;
        else
                calculated &= 0xFFFF;

        return provided == calculated;
}

static void ext4_inode_csum_set(struct inode *inode, struct ext4_inode *raw,
                                struct ext4_inode_info *ei)
{
        __u32 csum;

        if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
            cpu_to_le32(EXT4_OS_LINUX) ||
            !EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
                EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
                return;

        csum = ext4_inode_csum(inode, raw, ei);
        raw->i_checksum_lo = cpu_to_le16(csum & 0xFFFF);
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
            EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi))
                raw->i_checksum_hi = cpu_to_le16(csum >> 16);
}

static inline int ext4_begin_ordered_truncate(struct inode *inode,
                                              loff_t new_size)
{
        trace_ext4_begin_ordered_truncate(inode, new_size);
        /*
         * If jinode is zero, then we never opened the file for
         * writing, so there's no need to call
         * jbd2_journal_begin_ordered_truncate() since there's no
         * outstanding writes we need to flush.
         */
        if (!EXT4_I(inode)->jinode)
                return 0;
        return jbd2_journal_begin_ordered_truncate(EXT4_JOURNAL(inode),
                                                   EXT4_I(inode)->jinode,
                                                   new_size);
}

static void ext4_invalidatepage(struct page *page, unsigned long offset);
static int __ext4_journalled_writepage(struct page *page, unsigned int len);
static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh);
static int ext4_discard_partial_page_buffers_no_lock(handle_t *handle,
                struct inode *inode, struct page *page, loff_t from,
                loff_t length, int flags);

/*
 * Test whether an inode is a fast symlink.
 */
static int ext4_inode_is_fast_symlink(struct inode *inode)
{
        int ea_blocks = EXT4_I(inode)->i_file_acl ?
                (inode->i_sb->s_blocksize >> 9) : 0;

        return (S_ISLNK(inode->i_mode) && inode->i_blocks - ea_blocks == 0);
}

/*
 * Restart the transaction associated with *handle.  This does a commit,
 * so before we call here everything must be consistently dirtied against
 * this transaction.
 */
int ext4_truncate_restart_trans(handle_t *handle, struct inode *inode,
                                 int nblocks)
{
        int ret;

        /*
         * Drop i_data_sem to avoid deadlock with ext4_map_blocks.  At this
         * moment, get_block can be called only for blocks inside i_size since
         * page cache has been already dropped and writes are blocked by
         * i_mutex. So we can safely drop the i_data_sem here.
         */
        BUG_ON(EXT4_JOURNAL(inode) == NULL);
        jbd_debug(2, "restarting handle %p\n", handle);
        up_write(&EXT4_I(inode)->i_data_sem);
        ret = ext4_journal_restart(handle, nblocks);
        down_write(&EXT4_I(inode)->i_data_sem);
        ext4_discard_preallocations(inode);

        return ret;
}

/*
 * Called at the last iput() if i_nlink is zero.
 */
void ext4_evict_inode(struct inode *inode)
{
        handle_t *handle;
        int err;

        trace_ext4_evict_inode(inode);

        ext4_ioend_wait(inode);

        if (inode->i_nlink) {
                /*
                 * When journalling data dirty buffers are tracked only in the
                 * journal. So although mm thinks everything is clean and
                 * ready for reaping the inode might still have some pages to
                 * write in the running transaction or waiting to be
                 * checkpointed. Thus calling jbd2_journal_invalidatepage()
                 * (via truncate_inode_pages()) to discard these buffers can
                 * cause data loss. Also even if we did not discard these
                 * buffers, we would have no way to find them after the inode
                 * is reaped and thus user could see stale data if he tries to
                 * read them before the transaction is checkpointed. So be
                 * careful and force everything to disk here... We use
                 * ei->i_datasync_tid to store the newest transaction
                 * containing inode's data.
                 *
                 * Note that directories do not have this problem because they
                 * don't use page cache.
                 */
                if (ext4_should_journal_data(inode) &&
                    (S_ISLNK(inode->i_mode) || S_ISREG(inode->i_mode))) {
                        journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
                        tid_t commit_tid = EXT4_I(inode)->i_datasync_tid;

                        jbd2_log_start_commit(journal, commit_tid);
                        jbd2_log_wait_commit(journal, commit_tid);
                        filemap_write_and_wait(&inode->i_data);
                }
                truncate_inode_pages(&inode->i_data, 0);
                goto no_delete;
        }

        if (!is_bad_inode(inode))
                dquot_initialize(inode);

        if (ext4_should_order_data(inode))
                ext4_begin_ordered_truncate(inode, 0);
        truncate_inode_pages(&inode->i_data, 0);

        if (is_bad_inode(inode))
                goto no_delete;

        /*
         * Protect us against freezing - iput() caller didn't have to have any
         * protection against it
         */
        sb_start_intwrite(inode->i_sb);
        handle = ext4_journal_start(inode, ext4_blocks_for_truncate(inode)+3);
        if (IS_ERR(handle)) {
                ext4_std_error(inode->i_sb, PTR_ERR(handle));
                /*
                 * If we're going to skip the normal cleanup, we still need to
                 * make sure that the in-core orphan linked list is properly
                 * cleaned up.
                 */
                ext4_orphan_del(NULL, inode);
                sb_end_intwrite(inode->i_sb);
                goto no_delete;
        }

        if (IS_SYNC(inode))
                ext4_handle_sync(handle);
        inode->i_size = 0;
        err = ext4_mark_inode_dirty(handle, inode);
        if (err) {
                ext4_warning(inode->i_sb,
                             "couldn't mark inode dirty (err %d)", err);
                goto stop_handle;
        }
        if (inode->i_blocks)
                ext4_truncate(inode);

        /*
         * ext4_ext_truncate() doesn't reserve any slop when it
         * restarts journal transactions; therefore there may not be
         * enough credits left in the handle to remove the inode from
         * the orphan list and set the dtime field.
         */
        if (!ext4_handle_has_enough_credits(handle, 3)) {
                err = ext4_journal_extend(handle, 3);
                if (err > 0)
                        err = ext4_journal_restart(handle, 3);
                if (err != 0) {
                        ext4_warning(inode->i_sb,
                                     "couldn't extend journal (err %d)", err);
                stop_handle:
                        ext4_journal_stop(handle);
                        ext4_orphan_del(NULL, inode);
                        sb_end_intwrite(inode->i_sb);
                        goto no_delete;
                }
        }

        /*
         * Kill off the orphan record which ext4_truncate created.
         * AKPM: I think this can be inside the above `if'.
         * Note that ext4_orphan_del() has to be able to cope with the
         * deletion of a non-existent orphan - this is because we don't
         * know if ext4_truncate() actually created an orphan record.
         * (Well, we could do this if we need to, but heck - it works)
         */
        ext4_orphan_del(handle, inode);
        EXT4_I(inode)->i_dtime  = get_seconds();

        /*
         * One subtle ordering requirement: if anything has gone wrong
         * (transaction abort, IO errors, whatever), then we can still
         * do these next steps (the fs will already have been marked as
         * having errors), but we can't free the inode if the mark_dirty
         * fails.
         */
        if (ext4_mark_inode_dirty(handle, inode))
                /* If that failed, just do the required in-core inode clear. */
                ext4_clear_inode(inode);
        else
                ext4_free_inode(handle, inode);
        ext4_journal_stop(handle);
        sb_end_intwrite(inode->i_sb);
        return;
no_delete:
        ext4_clear_inode(inode);        /* We must guarantee clearing of inode... */
}

#ifdef CONFIG_QUOTA
qsize_t *ext4_get_reserved_space(struct inode *inode)
{
        return &EXT4_I(inode)->i_reserved_quota;
}
#endif

/*
 * Calculate the number of metadata blocks need to reserve
 * to allocate a block located at @lblock
 */
static int ext4_calc_metadata_amount(struct inode *inode, ext4_lblk_t lblock)
{
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                return ext4_ext_calc_metadata_amount(inode, lblock);

        return ext4_ind_calc_metadata_amount(inode, lblock);
}

/*
 * Called with i_data_sem down, which is important since we can call
 * ext4_discard_preallocations() from here.
 */
void ext4_da_update_reserve_space(struct inode *inode,
                                        int used, int quota_claim)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct ext4_inode_info *ei = EXT4_I(inode);

        spin_lock(&ei->i_block_reservation_lock);
        trace_ext4_da_update_reserve_space(inode, used, quota_claim);
        if (unlikely(used > ei->i_reserved_data_blocks)) {
                ext4_msg(inode->i_sb, KERN_NOTICE, "%s: ino %lu, used %d "
                         "with only %d reserved data blocks",
                         __func__, inode->i_ino, used,
                         ei->i_reserved_data_blocks);
                WARN_ON(1);
                used = ei->i_reserved_data_blocks;
        }

        if (unlikely(ei->i_allocated_meta_blocks > ei->i_reserved_meta_blocks)) {
                ext4_msg(inode->i_sb, KERN_NOTICE, "%s: ino %lu, allocated %d "
                         "with only %d reserved metadata blocks\n", __func__,
                         inode->i_ino, ei->i_allocated_meta_blocks,
                         ei->i_reserved_meta_blocks);
                WARN_ON(1);
                ei->i_allocated_meta_blocks = ei->i_reserved_meta_blocks;
        }

        /* Update per-inode reservations */
        ei->i_reserved_data_blocks -= used;
        ei->i_reserved_meta_blocks -= ei->i_allocated_meta_blocks;
        percpu_counter_sub(&sbi->s_dirtyclusters_counter,
                           used + ei->i_allocated_meta_blocks);
        ei->i_allocated_meta_blocks = 0;

        if (ei->i_reserved_data_blocks == 0) {
                /*
                 * We can release all of the reserved metadata blocks
                 * only when we have written all of the delayed
                 * allocation blocks.
                 */
                percpu_counter_sub(&sbi->s_dirtyclusters_counter,
                                   ei->i_reserved_meta_blocks);
                ei->i_reserved_meta_blocks = 0;
                ei->i_da_metadata_calc_len = 0;
        }
        spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

        /* Update quota subsystem for data blocks */
        if (quota_claim)
                dquot_claim_block(inode, EXT4_C2B(sbi, used));
        else {
                /*
                 * We did fallocate with an offset that is already delayed
                 * allocated. So on delayed allocated writeback we should
                 * not re-claim the quota for fallocated blocks.
                 */
                dquot_release_reservation_block(inode, EXT4_C2B(sbi, used));
        }

        /*
         * If we have done all the pending block allocations and if
         * there aren't any writers on the inode, we can discard the
         * inode's preallocations.
         */
        if ((ei->i_reserved_data_blocks == 0) &&
            (atomic_read(&inode->i_writecount) == 0))
                ext4_discard_preallocations(inode);
}

static int __check_block_validity(struct inode *inode, const char *func,
                                unsigned int line,
                                struct ext4_map_blocks *map)
{
        if (!ext4_data_block_valid(EXT4_SB(inode->i_sb), map->m_pblk,
                                   map->m_len)) {
                ext4_error_inode(inode, func, line, map->m_pblk,
                                 "lblock %lu mapped to illegal pblock "
                                 "(length %d)", (unsigned long) map->m_lblk,
                                 map->m_len);
                return -EIO;
        }
        return 0;
}

#define check_block_validity(inode, map)        \
        __check_block_validity((inode), __func__, __LINE__, (map))

/*
 * Return the number of contiguous dirty pages in a given inode
 * starting at page frame idx.
 */
static pgoff_t ext4_num_dirty_pages(struct inode *inode, pgoff_t idx,
                                    unsigned int max_pages)
{
        struct address_space *mapping = inode->i_mapping;
        pgoff_t index;
        struct pagevec pvec;
        pgoff_t num = 0;
        int i, nr_pages, done = 0;

        if (max_pages == 0)
                return 0;
        pagevec_init(&pvec, 0);
        while (!done) {
                index = idx;
                nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
                                              PAGECACHE_TAG_DIRTY,
                                              (pgoff_t)PAGEVEC_SIZE);
                if (nr_pages == 0)
                        break;
                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];
                        struct buffer_head *bh, *head;

                        lock_page(page);
                        if (unlikely(page->mapping != mapping) ||
                            !PageDirty(page) ||
                            PageWriteback(page) ||
                            page->index != idx) {
                                done = 1;
                                unlock_page(page);
                                break;
                        }
                        if (page_has_buffers(page)) {
                                bh = head = page_buffers(page);
                                do {
                                        if (!buffer_delay(bh) &&
                                            !buffer_unwritten(bh))
                                                done = 1;
                                        bh = bh->b_this_page;
                                } while (!done && (bh != head));
                        }
                        unlock_page(page);
                        if (done)
                                break;
                        idx++;
                        num++;
                        if (num >= max_pages) {
                                done = 1;
                                break;
                        }
                }
                pagevec_release(&pvec);
        }
        return num;
}

/*
 * The ext4_map_blocks() function tries to look up the requested blocks,
 * and returns if the blocks are already mapped.
 *
 * Otherwise it takes the write lock of the i_data_sem and allocate blocks
 * and store the allocated blocks in the result buffer head and mark it
 * mapped.
 *
 * If file type is extents based, it will call ext4_ext_map_blocks(),
 * Otherwise, call with ext4_ind_map_blocks() to handle indirect mapping
 * based files
 *
 * On success, it returns the number of blocks being mapped or allocate.
 * if create==0 and the blocks are pre-allocated and uninitialized block,
 * the result buffer head is unmapped. If the create ==1, it will make sure
 * the buffer head is mapped.
 *
 * It returns 0 if plain look up failed (blocks have not been allocated), in
 * that case, buffer head is unmapped
 *
 * It returns the error in case of allocation failure.
 */
int ext4_map_blocks(handle_t *handle, struct inode *inode,
                    struct ext4_map_blocks *map, int flags)
{
        int retval;

        map->m_flags = 0;
        ext_debug("ext4_map_blocks(): inode %lu, flag %d, max_blocks %u,"
                  "logical block %lu\n", inode->i_ino, flags, map->m_len,
                  (unsigned long) map->m_lblk);
        /*
         * Try to see if we can get the block without requesting a new
         * file system block.
         */
        if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
                down_read((&EXT4_I(inode)->i_data_sem));
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
                retval = ext4_ext_map_blocks(handle, inode, map, flags &
                                             EXT4_GET_BLOCKS_KEEP_SIZE);
        } else {
                retval = ext4_ind_map_blocks(handle, inode, map, flags &
                                             EXT4_GET_BLOCKS_KEEP_SIZE);
        }
        if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
                up_read((&EXT4_I(inode)->i_data_sem));

        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
                int ret;
                if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) {
                        /* delayed alloc may be allocated by fallocate and
                         * coverted to initialized by directIO.
                         * we need to handle delayed extent here.
                         */
                        down_write((&EXT4_I(inode)->i_data_sem));
                        goto delayed_mapped;
                }
                ret = check_block_validity(inode, map);
                if (ret != 0)
                        return ret;
        }

        /* If it is only a block(s) look up */
        if ((flags & EXT4_GET_BLOCKS_CREATE) == 0)
                return retval;

        /*
         * Returns if the blocks have already allocated
         *
         * Note that if blocks have been preallocated
         * ext4_ext_get_block() returns the create = 0
         * with buffer head unmapped.
         */
        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED)
                return retval;

        /*
         * When we call get_blocks without the create flag, the
         * BH_Unwritten flag could have gotten set if the blocks
         * requested were part of a uninitialized extent.  We need to
         * clear this flag now that we are committed to convert all or
         * part of the uninitialized extent to be an initialized
         * extent.  This is because we need to avoid the combination
         * of BH_Unwritten and BH_Mapped flags being simultaneously
         * set on the buffer_head.
         */
        map->m_flags &= ~EXT4_MAP_UNWRITTEN;

        /*
         * New blocks allocate and/or writing to uninitialized extent
         * will possibly result in updating i_data, so we take
         * the write lock of i_data_sem, and call get_blocks()
         * with create == 1 flag.
         */
        down_write((&EXT4_I(inode)->i_data_sem));

        /*
         * if the caller is from delayed allocation writeout path
         * we have already reserved fs blocks for allocation
         * let the underlying get_block() function know to
         * avoid double accounting
         */
        if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
                ext4_set_inode_state(inode, EXT4_STATE_DELALLOC_RESERVED);
        /*
         * We need to check for EXT4 here because migrate
         * could have changed the inode type in between
         */
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
                retval = ext4_ext_map_blocks(handle, inode, map, flags);
        } else {
                retval = ext4_ind_map_blocks(handle, inode, map, flags);

                if (retval > 0 && map->m_flags & EXT4_MAP_NEW) {
                        /*
                         * We allocated new blocks which will result in
                         * i_data's format changing.  Force the migrate
                         * to fail by clearing migrate flags
                         */
                        ext4_clear_inode_state(inode, EXT4_STATE_EXT_MIGRATE);
                }

                /*
                 * Update reserved blocks/metadata blocks after successful
                 * block allocation which had been deferred till now. We don't
                 * support fallocate for non extent files. So we can update
                 * reserve space here.
                 */
                if ((retval > 0) &&
                        (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE))
                        ext4_da_update_reserve_space(inode, retval, 1);
        }
        if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) {
                ext4_clear_inode_state(inode, EXT4_STATE_DELALLOC_RESERVED);

                if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
                        int ret;
delayed_mapped:
                        /* delayed allocation blocks has been allocated */
                        ret = ext4_es_remove_extent(inode, map->m_lblk,
                                                    map->m_len);
                        if (ret < 0)
                                retval = ret;
                }
        }

        up_write((&EXT4_I(inode)->i_data_sem));
        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
                int ret = check_block_validity(inode, map);
                if (ret != 0)
                        return ret;
        }
        return retval;
}

/* Maximum number of blocks we map for direct IO at once. */
#define DIO_MAX_BLOCKS 4096

static int _ext4_get_block(struct inode *inode, sector_t iblock,
                           struct buffer_head *bh, int flags)
{
        handle_t *handle = ext4_journal_current_handle();
        struct ext4_map_blocks map;
        int ret = 0, started = 0;
        int dio_credits;

        if (ext4_has_inline_data(inode))
                return -ERANGE;

        map.m_lblk = iblock;
        map.m_len = bh->b_size >> inode->i_blkbits;

        if (flags && !(flags & EXT4_GET_BLOCKS_NO_LOCK) && !handle) {
                /* Direct IO write... */
                if (map.m_len > DIO_MAX_BLOCKS)
                        map.m_len = DIO_MAX_BLOCKS;
                dio_credits = ext4_chunk_trans_blocks(inode, map.m_len);
                handle = ext4_journal_start(inode, dio_credits);
                if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        return ret;
                }
                started = 1;
        }

        ret = ext4_map_blocks(handle, inode, &map, flags);
        if (ret > 0) {
                map_bh(bh, inode->i_sb, map.m_pblk);
                bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;
                bh->b_size = inode->i_sb->s_blocksize * map.m_len;
                ret = 0;
        }
        if (started)
                ext4_journal_stop(handle);
        return ret;
}

int ext4_get_block(struct inode *inode, sector_t iblock,
                   struct buffer_head *bh, int create)
{
        return _ext4_get_block(inode, iblock, bh,
                               create ? EXT4_GET_BLOCKS_CREATE : 0);
}

/*
 * `handle' can be NULL if create is zero
 */
struct buffer_head *ext4_getblk(handle_t *handle, struct inode *inode,
                                ext4_lblk_t block, int create, int *errp)
{
        struct ext4_map_blocks map;
        struct buffer_head *bh;
        int fatal = 0, err;

        J_ASSERT(handle != NULL || create == 0);

        map.m_lblk = block;
        map.m_len = 1;
        err = ext4_map_blocks(handle, inode, &map,
                              create ? EXT4_GET_BLOCKS_CREATE : 0);

        /* ensure we send some value back into *errp */
        *errp = 0;

        if (err < 0)
                *errp = err;
        if (err <= 0)
                return NULL;

        bh = sb_getblk(inode->i_sb, map.m_pblk);
        if (unlikely(!bh)) {
                *errp = -ENOMEM;
                return NULL;
        }
        if (map.m_flags & EXT4_MAP_NEW) {
                J_ASSERT(create != 0);
                J_ASSERT(handle != NULL);

                /*
                 * Now that we do not always journal data, we should
                 * keep in mind whether this should always journal the
                 * new buffer as metadata.  For now, regular file
                 * writes use ext4_get_block instead, so it's not a
                 * problem.
                 */
                lock_buffer(bh);
                BUFFER_TRACE(bh, "call get_create_access");
                fatal = ext4_journal_get_create_access(handle, bh);
                if (!fatal && !buffer_uptodate(bh)) {
                        memset(bh->b_data, 0, inode->i_sb->s_blocksize);
                        set_buffer_uptodate(bh);
                }
                unlock_buffer(bh);
                BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
                err = ext4_handle_dirty_metadata(handle, inode, bh);
                if (!fatal)
                        fatal = err;
        } else {
                BUFFER_TRACE(bh, "not a new buffer");
        }
        if (fatal) {
                *errp = fatal;
                brelse(bh);
                bh = NULL;
        }
        return bh;
}

struct buffer_head *ext4_bread(handle_t *handle, struct inode *inode,
                               ext4_lblk_t block, int create, int *err)
{
        struct buffer_head *bh;

        bh = ext4_getblk(handle, inode, block, create, err);
        if (!bh)
                return bh;
        if (buffer_uptodate(bh))
                return bh;
        ll_rw_block(READ | REQ_META | REQ_PRIO, 1, &bh);
        wait_on_buffer(bh);
        if (buffer_uptodate(bh))
                return bh;
        put_bh(bh);
        *err = -EIO;
        return NULL;
}

int ext4_walk_page_buffers(handle_t *handle,
                           struct buffer_head *head,
                           unsigned from,
                           unsigned to,
                           int *partial,
                           int (*fn)(handle_t *handle,
                                     struct buffer_head *bh))
{
        struct buffer_head *bh;
        unsigned block_start, block_end;
        unsigned blocksize = head->b_size;
        int err, ret = 0;
        struct buffer_head *next;

        for (bh = head, block_start = 0;
             ret == 0 && (bh != head || !block_start);
             block_start = block_end, bh = next) {
                next = bh->b_this_page;
                block_end = block_start + blocksize;
                if (block_end <= from || block_start >= to) {
                        if (partial && !buffer_uptodate(bh))
                                *partial = 1;
                        continue;
                }
                err = (*fn)(handle, bh);
                if (!ret)
                        ret = err;
        }
        return ret;
}

/*
 * To preserve ordering, it is essential that the hole instantiation and
 * the data write be encapsulated in a single transaction.  We cannot
 * close off a transaction and start a new one between the ext4_get_block()
 * and the commit_write().  So doing the jbd2_journal_start at the start of
 * prepare_write() is the right place.
 *
 * Also, this function can nest inside ext4_writepage().  In that case, we
 * *know* that ext4_writepage() has generated enough buffer credits to do the
 * whole page.  So we won't block on the journal in that case, which is good,
 * because the caller may be PF_MEMALLOC.
 *
 * By accident, ext4 can be reentered when a transaction is open via
 * quota file writes.  If we were to commit the transaction while thus
 * reentered, there can be a deadlock - we would be holding a quota
 * lock, and the commit would never complete if another thread had a
 * transaction open and was blocking on the quota lock - a ranking
 * violation.
 *
 * So what we do is to rely on the fact that jbd2_journal_stop/journal_start
 * will _not_ run commit under these circumstances because handle->h_ref
 * is elevated.  We'll still have enough credits for the tiny quotafile
 * write.
 */
int do_journal_get_write_access(handle_t *handle,
                                struct buffer_head *bh)
{
        int dirty = buffer_dirty(bh);
        int ret;

        if (!buffer_mapped(bh) || buffer_freed(bh))
                return 0;
        /*
         * __block_write_begin() could have dirtied some buffers. Clean
         * the dirty bit as jbd2_journal_get_write_access() could complain
         * otherwise about fs integrity issues. Setting of the dirty bit
         * by __block_write_begin() isn't a real problem here as we clear
         * the bit before releasing a page lock and thus writeback cannot
         * ever write the buffer.
         */
        if (dirty)
                clear_buffer_dirty(bh);
        ret = ext4_journal_get_write_access(handle, bh);
        if (!ret && dirty)
                ret = ext4_handle_dirty_metadata(handle, NULL, bh);
        return ret;
}

static int ext4_get_block_write_nolock(struct inode *inode, sector_t iblock,
                   struct buffer_head *bh_result, int create);
static int ext4_write_begin(struct file *file, struct address_space *mapping,
                            loff_t pos, unsigned len, unsigned flags,
                            struct page **pagep, void **fsdata)
{
        struct inode *inode = mapping->host;
        int ret, needed_blocks;
        handle_t *handle;
        int retries = 0;
        struct page *page;
        pgoff_t index;
        unsigned from, to;

        trace_ext4_write_begin(inode, pos, len, flags);
        /*
         * Reserve one block more for addition to orphan list in case
         * we allocate blocks but write fails for some reason
         */
        needed_blocks = ext4_writepage_trans_blocks(inode) + 1;
        index = pos >> PAGE_CACHE_SHIFT;
        from = pos & (PAGE_CACHE_SIZE - 1);
        to = from + len;

        if (ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)) {
                ret = ext4_try_to_write_inline_data(mapping, inode, pos, len,
                                                    flags, pagep);
                if (ret < 0)
                        goto out;
                if (ret == 1) {
                        ret = 0;
                        goto out;
                }
        }

retry:
        handle = ext4_journal_start(inode, needed_blocks);
        if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                goto out;
        }

        /* We cannot recurse into the filesystem as the transaction is already
         * started */
        flags |= AOP_FLAG_NOFS;

        page = grab_cache_page_write_begin(mapping, index, flags);
        if (!page) {
                ext4_journal_stop(handle);
                ret = -ENOMEM;
                goto out;
        }

        *pagep = page;

        if (ext4_should_dioread_nolock(inode))
                ret = __block_write_begin(page, pos, len, ext4_get_block_write);
        else
                ret = __block_write_begin(page, pos, len, ext4_get_block);

        if (!ret && ext4_should_journal_data(inode)) {
                ret = ext4_walk_page_buffers(handle, page_buffers(page),
                                             from, to, NULL,
                                             do_journal_get_write_access);
        }

        if (ret) {
                unlock_page(page);
                page_cache_release(page);
                /*
                 * __block_write_begin may have instantiated a few blocks
                 * outside i_size.  Trim these off again. Don't need
                 * i_size_read because we hold i_mutex.
                 *
                 * Add inode to orphan list in case we crash before
                 * truncate finishes
                 */
                if (pos + len > inode->i_size && ext4_can_truncate(inode))
                        ext4_orphan_add(handle, inode);

                ext4_journal_stop(handle);
                if (pos + len > inode->i_size) {
                        ext4_truncate_failed_write(inode);
                        /*
                         * If truncate failed early the inode might
                         * still be on the orphan list; we need to
                         * make sure the inode is removed from the
                         * orphan list in that case.
                         */
                        if (inode->i_nlink)
                                ext4_orphan_del(NULL, inode);
                }
        }

        if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
                goto retry;
out:
        return ret;
}

/* For write_end() in data=journal mode */
static int write_end_fn(handle_t *handle, struct buffer_head *bh)
{
        if (!buffer_mapped(bh) || buffer_freed(bh))
                return 0;
        set_buffer_uptodate(bh);
        return ext4_handle_dirty_metadata(handle, NULL, bh);
}

static int ext4_generic_write_end(struct file *file,
                                  struct address_space *mapping,
                                  loff_t pos, unsigned len, unsigned copied,
                                  struct page *page, void *fsdata)
{
        int i_size_changed = 0;
        struct inode *inode = mapping->host;
        handle_t *handle = ext4_journal_current_handle();

        if (ext4_has_inline_data(inode))
                copied = ext4_write_inline_data_end(inode, pos, len,
                                                    copied, page);
        else
                copied = block_write_end(file, mapping, pos,
                                         len, copied, page, fsdata);

        /*
         * No need to use i_size_read() here, the i_size
         * cannot change under us because we hold i_mutex.
         *
         * But it's important to update i_size while still holding page lock:
         * page writeout could otherwise come in and zero beyond i_size.
         */
        if (pos + copied > inode->i_size) {
                i_size_write(inode, pos + copied);
                i_size_changed = 1;
        }

        if (pos + copied >  EXT4_I(inode)->i_disksize) {
                /* We need to mark inode dirty even if
                 * new_i_size is less that inode->i_size
                 * bu greater than i_disksize.(hint delalloc)
                 */
                ext4_update_i_disksize(inode, (pos + copied));
                i_size_changed = 1;
        }
        unlock_page(page);
        page_cache_release(page);

        /*
         * Don't mark the inode dirty under page lock. First, it unnecessarily
         * makes the holding time of page lock longer. Second, it forces lock
         * ordering of page lock and transaction start for journaling
         * filesystems.
         */
        if (i_size_changed)
                ext4_mark_inode_dirty(handle, inode);

        return copied;
}

/*
 * We need to pick up the new inode size which generic_commit_write gave us
 * `file' can be NULL - eg, when called from page_symlink().
 *
 * ext4 never places buffers on inode->i_mapping->private_list.  metadata
 * buffers are managed internally.
 */
static int ext4_ordered_write_end(struct file *file,
                                  struct address_space *mapping,
                                  loff_t pos, unsigned len, unsigned copied,
                                  struct page *page, void *fsdata)
{
        handle_t *handle = ext4_journal_current_handle();
        struct inode *inode = mapping->host;
        int ret = 0, ret2;

        trace_ext4_ordered_write_end(inode, pos, len, copied);
        ret = ext4_jbd2_file_inode(handle, inode);

        if (ret == 0) {
                ret2 = ext4_generic_write_end(file, mapping, pos, len, copied,
                                                        page, fsdata);
                copied = ret2;
                if (pos + len > inode->i_size && ext4_can_truncate(inode))
                        /* if we have allocated more blocks and copied
                         * less. We will have blocks allocated outside
                         * inode->i_size. So truncate them
                         */
                        ext4_orphan_add(handle, inode);
                if (ret2 < 0)
                        ret = ret2;
        } else {
                unlock_page(page);
                page_cache_release(page);
        }

        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;

        if (pos + len > inode->i_size) {
                ext4_truncate_failed_write(inode);
                /*
                 * If truncate failed early the inode might still be
                 * on the orphan list; we need to make sure the inode
                 * is removed from the orphan list in that case.
                 */
                if (inode->i_nlink)
                        ext4_orphan_del(NULL, inode);
        }


        return ret ? ret : copied;
}

static int ext4_writeback_write_end(struct file *file,
                                    struct address_space *mapping,
                                    loff_t pos, unsigned len, unsigned copied,
                                    struct page *page, void *fsdata)
{
        handle_t *handle = ext4_journal_current_handle();
        struct inode *inode = mapping->host;
        int ret = 0, ret2;

        trace_ext4_writeback_write_end(inode, pos, len, copied);
        ret2 = ext4_generic_write_end(file, mapping, pos, len, copied,
                                                        page, fsdata);
        copied = ret2;
        if (pos + len > inode->i_size && ext4_can_truncate(inode))
                /* if we have allocated more blocks and copied
                 * less. We will have blocks allocated outside
                 * inode->i_size. So truncate them
                 */
                ext4_orphan_add(handle, inode);

        if (ret2 < 0)
                ret = ret2;

        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;

        if (pos + len > inode->i_size) {
                ext4_truncate_failed_write(inode);
                /*
                 * If truncate failed early the inode might still be
                 * on the orphan list; we need to make sure the inode
                 * is removed from the orphan list in that case.
                 */
                if (inode->i_nlink)
                        ext4_orphan_del(NULL, inode);
        }

        return ret ? ret : copied;
}

static int ext4_journalled_write_end(struct file *file,
                                     struct address_space *mapping,
                                     loff_t pos, unsigned len, unsigned copied,
                                     struct page *page, void *fsdata)
{
        handle_t *handle = ext4_journal_current_handle();
        struct inode *inode = mapping->host;
        int ret = 0, ret2;
        int partial = 0;
        unsigned from, to;
        loff_t new_i_size;

        trace_ext4_journalled_write_end(inode, pos, len, copied);
        from = pos & (PAGE_CACHE_SIZE - 1);
        to = from + len;

        BUG_ON(!ext4_handle_valid(handle));

        if (ext4_has_inline_data(inode))
                copied = ext4_write_inline_data_end(inode, pos, len,
                                                    copied, page);
        else {
                if (copied < len) {
                        if (!PageUptodate(page))
                                copied = 0;
                        page_zero_new_buffers(page, from+copied, to);
                }

                ret = ext4_walk_page_buffers(handle, page_buffers(page), from,
                                             to, &partial, write_end_fn);
                if (!partial)
                        SetPageUptodate(page);
        }
        new_i_size = pos + copied;
        if (new_i_size > inode->i_size)
                i_size_write(inode, pos+copied);
        ext4_set_inode_state(inode, EXT4_STATE_JDATA);
        EXT4_I(inode)->i_datasync_tid = handle->h_transaction->t_tid;
        if (new_i_size > EXT4_I(inode)->i_disksize) {
                ext4_update_i_disksize(inode, new_i_size);
                ret2 = ext4_mark_inode_dirty(handle, inode);
                if (!ret)
                        ret = ret2;
        }

        unlock_page(page);
        page_cache_release(page);
        if (pos + len > inode->i_size && ext4_can_truncate(inode))
                /* if we have allocated more blocks and copied
                 * less. We will have blocks allocated outside
                 * inode->i_size. So truncate them
                 */
                ext4_orphan_add(handle, inode);

        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;
        if (pos + len > inode->i_size) {
                ext4_truncate_failed_write(inode);
                /*
                 * If truncate failed early the inode might still be
                 * on the orphan list; we need to make sure the inode
                 * is removed from the orphan list in that case.
                 */
                if (inode->i_nlink)
                        ext4_orphan_del(NULL, inode);
        }

        return ret ? ret : copied;
}

/*
 * Reserve a single cluster located at lblock
 */
static int ext4_da_reserve_space(struct inode *inode, ext4_lblk_t lblock)
{
        int retries = 0;
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct ext4_inode_info *ei = EXT4_I(inode);
        unsigned int md_needed;
        int ret;
        ext4_lblk_t save_last_lblock;
        int save_len;

        /*
         * We will charge metadata quota at writeout time; this saves
         * us from metadata over-estimation, though we may go over by
         * a small amount in the end.  Here we just reserve for data.
         */
        ret = dquot_reserve_block(inode, EXT4_C2B(sbi, 1));
        if (ret)
                return ret;

        /*
         * recalculate the amount of metadata blocks to reserve
         * in order to allocate nrblocks
         * worse case is one extent per block
         */
repeat:
        spin_lock(&ei->i_block_reservation_lock);
        /*
         * ext4_calc_metadata_amount() has side effects, which we have
         * to be prepared undo if we fail to claim space.
         */
        save_len = ei->i_da_metadata_calc_len;
        save_last_lblock = ei->i_da_metadata_calc_last_lblock;
        md_needed = EXT4_NUM_B2C(sbi,
                                 ext4_calc_metadata_amount(inode, lblock));
        trace_ext4_da_reserve_space(inode, md_needed);

        /*
         * We do still charge estimated metadata to the sb though;
         * we cannot afford to run out of free blocks.
         */
        if (ext4_claim_free_clusters(sbi, md_needed + 1, 0)) {
                ei->i_da_metadata_calc_len = save_len;
                ei->i_da_metadata_calc_last_lblock = save_last_lblock;
                spin_unlock(&ei->i_block_reservation_lock);
                if (ext4_should_retry_alloc(inode->i_sb, &retries)) {
                        yield();
                        goto repeat;
                }
                dquot_release_reservation_block(inode, EXT4_C2B(sbi, 1));
                return -ENOSPC;
        }
        ei->i_reserved_data_blocks++;
        ei->i_reserved_meta_blocks += md_needed;
        spin_unlock(&ei->i_block_reservation_lock);

        return 0;       /* success */
}

static void ext4_da_release_space(struct inode *inode, int to_free)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct ext4_inode_info *ei = EXT4_I(inode);

        if (!to_free)
                return;         /* Nothing to release, exit */

        spin_lock(&EXT4_I(inode)->i_block_reservation_lock);

        trace_ext4_da_release_space(inode, to_free);
        if (unlikely(to_free > ei->i_reserved_data_blocks)) {
                /*
                 * if there aren't enough reserved blocks, then the
                 * counter is messed up somewhere.  Since this
                 * function is called from invalidate page, it's
                 * harmless to return without any action.
                 */
                ext4_msg(inode->i_sb, KERN_NOTICE, "ext4_da_release_space: "
                         "ino %lu, to_free %d with only %d reserved "
                         "data blocks", inode->i_ino, to_free,
                         ei->i_reserved_data_blocks);
                WARN_ON(1);
                to_free = ei->i_reserved_data_blocks;
        }
        ei->i_reserved_data_blocks -= to_free;

        if (ei->i_reserved_data_blocks == 0) {
                /*
                 * We can release all of the reserved metadata blocks
                 * only when we have written all of the delayed
                 * allocation blocks.
                 * Note that in case of bigalloc, i_reserved_meta_blocks,
                 * i_reserved_data_blocks, etc. refer to number of clusters.
                 */
                percpu_counter_sub(&sbi->s_dirtyclusters_counter,
                                   ei->i_reserved_meta_blocks);
                ei->i_reserved_meta_blocks = 0;
                ei->i_da_metadata_calc_len = 0;
        }

        /* update fs dirty data blocks counter */
        percpu_counter_sub(&sbi->s_dirtyclusters_counter, to_free);

        spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

        dquot_release_reservation_block(inode, EXT4_C2B(sbi, to_free));
}

static void ext4_da_page_release_reservation(struct page *page,
                                             unsigned long offset)
{
        int to_release = 0;
        struct buffer_head *head, *bh;
        unsigned int curr_off = 0;
        struct inode *inode = page->mapping->host;
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        int num_clusters;
        ext4_fsblk_t lblk;

        head = page_buffers(page);
        bh = head;
        do {
                unsigned int next_off = curr_off + bh->b_size;

                if ((offset <= curr_off) && (buffer_delay(bh))) {
                        to_release++;
                        clear_buffer_delay(bh);
                }
                curr_off = next_off;
        } while ((bh = bh->b_this_page) != head);

        if (to_release) {
                lblk = page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
                ext4_es_remove_extent(inode, lblk, to_release);
        }

        /* If we have released all the blocks belonging to a cluster, then we
         * need to release the reserved space for that cluster. */
        num_clusters = EXT4_NUM_B2C(sbi, to_release);
        while (num_clusters > 0) {
                lblk = (page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits)) +
                        ((num_clusters - 1) << sbi->s_cluster_bits);
                if (sbi->s_cluster_ratio == 1 ||
                    !ext4_find_delalloc_cluster(inode, lblk))
                        ext4_da_release_space(inode, 1);

                num_clusters--;
        }
}

/*
 * Delayed allocation stuff
 */

/*
 * mpage_da_submit_io - walks through extent of pages and try to write
 * them with writepage() call back
 *
 * @mpd->inode: inode
 * @mpd->first_page: first page of the extent
 * @mpd->next_page: page after the last page of the extent
 *
 * By the time mpage_da_submit_io() is called we expect all blocks
 * to be allocated. this may be wrong if allocation failed.
 *
 * As pages are already locked by write_cache_pages(), we can't use it
 */
static int mpage_da_submit_io(struct mpage_da_data *mpd,
                              struct ext4_map_blocks *map)
{
        struct pagevec pvec;
        unsigned long index, end;
        int ret = 0, err, nr_pages, i;
        struct inode *inode = mpd->inode;
        struct address_space *mapping = inode->i_mapping;
        loff_t size = i_size_read(inode);
        unsigned int len, block_start;
        struct buffer_head *bh, *page_bufs = NULL;
        sector_t pblock = 0, cur_logical = 0;
        struct ext4_io_submit io_submit;

        BUG_ON(mpd->next_page <= mpd->first_page);
        memset(&io_submit, 0, sizeof(io_submit));
        /*
         * We need to start from the first_page to the next_page - 1
         * to make sure we also write the mapped dirty buffer_heads.
         * If we look at mpd->b_blocknr we would only be looking
         * at the currently mapped buffer_heads.
         */
        index = mpd->first_page;
        end = mpd->next_page - 1;

        pagevec_init(&pvec, 0);
        while (index <= end) {
                nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
                if (nr_pages == 0)
                        break;
                for (i = 0; i < nr_pages; i++) {
                        int skip_page = 0;
                        struct page *page = pvec.pages[i];

                        index = page->index;
                        if (index > end)
                                break;

                        if (index == size >> PAGE_CACHE_SHIFT)
                                len = size & ~PAGE_CACHE_MASK;
                        else
                                len = PAGE_CACHE_SIZE;
                        if (map) {
                                cur_logical = index << (PAGE_CACHE_SHIFT -
                                                        inode->i_blkbits);
                                pblock = map->m_pblk + (cur_logical -
                                                        map->m_lblk);
                        }
                        index++;

                        BUG_ON(!PageLocked(page));
                        BUG_ON(PageWriteback(page));

                        bh = page_bufs = page_buffers(page);
                        block_start = 0;
                        do {
                                if (map && (cur_logical >= map->m_lblk) &&
                                    (cur_logical <= (map->m_lblk +
                                                     (map->m_len - 1)))) {
                                        if (buffer_delay(bh)) {
                                                clear_buffer_delay(bh);
                                                bh->b_blocknr = pblock;
                                        }
                                        if (buffer_unwritten(bh) ||
                                            buffer_mapped(bh))
                                                BUG_ON(bh->b_blocknr != pblock);
                                        if (map->m_flags & EXT4_MAP_UNINIT)
                                                set_buffer_uninit(bh);
                                        clear_buffer_unwritten(bh);
                                }

                                /*
                                 * skip page if block allocation undone and
                                 * block is dirty
                                 */
                                if (ext4_bh_delay_or_unwritten(NULL, bh))
                                        skip_page = 1;
                                bh = bh->b_this_page;
                                block_start += bh->b_size;
                                cur_logical++;
                                pblock++;
                        } while (bh != page_bufs);

                        if (skip_page) {
                                unlock_page(page);
                                continue;
                        }

                        clear_page_dirty_for_io(page);
                        err = ext4_bio_write_page(&io_submit, page, len,
                                                  mpd->wbc);
                        if (!err)
                                mpd->pages_written++;
                        /*
                         * In error case, we have to continue because
                         * remaining pages are still locked
                         */
                        if (ret == 0)
                                ret = err;
                }
                pagevec_release(&pvec);
        }
        ext4_io_submit(&io_submit);
        return ret;
}

static void ext4_da_block_invalidatepages(struct mpage_da_data *mpd)
{
        int nr_pages, i;
        pgoff_t index, end;
        struct pagevec pvec;
        struct inode *inode = mpd->inode;
        struct address_space *mapping = inode->i_mapping;
        ext4_lblk_t start, last;

        index = mpd->first_page;
        end   = mpd->next_page - 1;

        start = index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
        last = end << (PAGE_CACHE_SHIFT - inode->i_blkbits);
        ext4_es_remove_extent(inode, start, last - start + 1);

        pagevec_init(&pvec, 0);
        while (index <= end) {
                nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
                if (nr_pages == 0)
                        break;
                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];
                        if (page->index > end)
                                break;
                        BUG_ON(!PageLocked(page));
                        BUG_ON(PageWriteback(page));
                        block_invalidatepage(page, 0);
                        ClearPageUptodate(page);
                        unlock_page(page);
                }
                index = pvec.pages[nr_pages - 1]->index + 1;
                pagevec_release(&pvec);
        }
        return;
}

static void ext4_print_free_blocks(struct inode *inode)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct super_block *sb = inode->i_sb;

        ext4_msg(sb, KERN_CRIT, "Total free blocks count %lld",
               EXT4_C2B(EXT4_SB(inode->i_sb),
                        ext4_count_free_clusters(inode->i_sb)));
        ext4_msg(sb, KERN_CRIT, "Free/Dirty block details");
        ext4_msg(sb, KERN_CRIT, "free_blocks=%lld",
               (long long) EXT4_C2B(EXT4_SB(inode->i_sb),
                percpu_counter_sum(&sbi->s_freeclusters_counter)));
        ext4_msg(sb, KERN_CRIT, "dirty_blocks=%lld",
               (long long) EXT4_C2B(EXT4_SB(inode->i_sb),
                percpu_counter_sum(&sbi->s_dirtyclusters_counter)));
        ext4_msg(sb, KERN_CRIT, "Block reservation details");
        ext4_msg(sb, KERN_CRIT, "i_reserved_data_blocks=%u",
                 EXT4_I(inode)->i_reserved_data_blocks);
        ext4_msg(sb, KERN_CRIT, "i_reserved_meta_blocks=%u",
               EXT4_I(inode)->i_reserved_meta_blocks);
        return;
}

/*
 * mpage_da_map_and_submit - go through given space, map them
 *       if necessary, and then submit them for I/O
 *
 * @mpd - bh describing space
 *
 * The function skips space we know is already mapped to disk blocks.
 *
 */
static void mpage_da_map_and_submit(struct mpage_da_data *mpd)
{
        int err, blks, get_blocks_flags;
        struct ext4_map_blocks map, *mapp = NULL;
        sector_t next = mpd->b_blocknr;
        unsigned max_blocks = mpd->b_size >> mpd->inode->i_blkbits;
        loff_t disksize = EXT4_I(mpd->inode)->i_disksize;
        handle_t *handle = NULL;

        /*
         * If the blocks are mapped already, or we couldn't accumulate
         * any blocks, then proceed immediately to the submission stage.
         */
        if ((mpd->b_size == 0) ||
            ((mpd->b_state  & (1 << BH_Mapped)) &&
             !(mpd->b_state & (1 << BH_Delay)) &&
             !(mpd->b_state & (1 << BH_Unwritten))))
                goto submit_io;

        handle = ext4_journal_current_handle();
        BUG_ON(!handle);

        /*
         * Call ext4_map_blocks() to allocate any delayed allocation
         * blocks, or to convert an uninitialized extent to be
         * initialized (in the case where we have written into
         * one or more preallocated blocks).
         *
         * We pass in the magic EXT4_GET_BLOCKS_DELALLOC_RESERVE to
         * indicate that we are on the delayed allocation path.  This
         * affects functions in many different parts of the allocation
         * call path.  This flag exists primarily because we don't
         * want to change *many* call functions, so ext4_map_blocks()
         * will set the EXT4_STATE_DELALLOC_RESERVED flag once the
         * inode's allocation semaphore is taken.
         *
         * If the blocks in questions were delalloc blocks, set
         * EXT4_GET_BLOCKS_DELALLOC_RESERVE so the delalloc accounting
         * variables are updated after the blocks have been allocated.
         */
        map.m_lblk = next;
        map.m_len = max_blocks;
        get_blocks_flags = EXT4_GET_BLOCKS_CREATE;
        if (ext4_should_dioread_nolock(mpd->inode))
                get_blocks_flags |= EXT4_GET_BLOCKS_IO_CREATE_EXT;
        if (mpd->b_state & (1 << BH_Delay))
                get_blocks_flags |= EXT4_GET_BLOCKS_DELALLOC_RESERVE;

        blks = ext4_map_blocks(handle, mpd->inode, &map, get_blocks_flags);
        if (blks < 0) {
                struct super_block *sb = mpd->inode->i_sb;

                err = blks;
                /*
                 * If get block returns EAGAIN or ENOSPC and there
                 * appears to be free blocks we will just let
                 * mpage_da_submit_io() unlock all of the pages.
                 */
                if (err == -EAGAIN)
                        goto submit_io;

                if (err == -ENOSPC && ext4_count_free_clusters(sb)) {
                        mpd->retval = err;
                        goto submit_io;
                }

                /*
                 * get block failure will cause us to loop in
                 * writepages, because a_ops->writepage won't be able
                 * to make progress. The page will be redirtied by
                 * writepage and writepages will again try to write
                 * the same.
                 */
                if (!(EXT4_SB(sb)->s_mount_flags & EXT4_MF_FS_ABORTED)) {
                        ext4_msg(sb, KERN_CRIT,
                                 "delayed block allocation failed for inode %lu "
                                 "at logical offset %llu with max blocks %zd "
                                 "with error %d", mpd->inode->i_ino,
                                 (unsigned long long) next,
                                 mpd->b_size >> mpd->inode->i_blkbits, err);
                        ext4_msg(sb, KERN_CRIT,
                                "This should not happen!! Data will be lost\n");
                        if (err == -ENOSPC)
                                ext4_print_free_blocks(mpd->inode);
                }
                /* invalidate all the pages */
                ext4_da_block_invalidatepages(mpd);

                /* Mark this page range as having been completed */
                mpd->io_done = 1;
                return;
        }
        BUG_ON(blks == 0);

        mapp = &map;
        if (map.m_flags & EXT4_MAP_NEW) {
                struct block_device *bdev = mpd->inode->i_sb->s_bdev;
                int i;

                for (i = 0; i < map.m_len; i++)
                        unmap_underlying_metadata(bdev, map.m_pblk + i);
        }

        /*
         * Update on-disk size along with block allocation.
         */
        disksize = ((loff_t) next + blks) << mpd->inode->i_blkbits;
        if (disksize > i_size_read(mpd->inode))
                disksize = i_size_read(mpd->inode);
        if (disksize > EXT4_I(mpd->inode)->i_disksize) {
                ext4_update_i_disksize(mpd->inode, disksize);
                err = ext4_mark_inode_dirty(handle, mpd->inode);
                if (err)
                        ext4_error(mpd->inode->i_sb,
                                   "Failed to mark inode %lu dirty",
                                   mpd->inode->i_ino);
        }

submit_io:
        mpage_da_submit_io(mpd, mapp);
        mpd->io_done = 1;
}

#define BH_FLAGS ((1 << BH_Uptodate) | (1 << BH_Mapped) | \
                (1 << BH_Delay) | (1 << BH_Unwritten))

/*
 * mpage_add_bh_to_extent - try to add one more block to extent of blocks
 *
 * @mpd->lbh - extent of blocks
 * @logical - logical number of the block in the file
 * @bh - bh of the block (used to access block's state)
 *
 * the function is used to collect contig. blocks in same state
 */
static void mpage_add_bh_to_extent(struct mpage_da_data *mpd,
                                   sector_t logical, size_t b_size,
                                   unsigned long b_state)
{
        sector_t next;
        int nrblocks = mpd->b_size >> mpd->inode->i_blkbits;

        /*
         * XXX Don't go larger than mballoc is willing to allocate
         * This is a stopgap solution.  We eventually need to fold
         * mpage_da_submit_io() into this function and then call
         * ext4_map_blocks() multiple times in a loop
         */
        if (nrblocks >= 8*1024*1024/mpd->inode->i_sb->s_blocksize)
                goto flush_it;

        /* check if thereserved journal credits might overflow */
        if (!(ext4_test_inode_flag(mpd->inode, EXT4_INODE_EXTENTS))) {
                if (nrblocks >= EXT4_MAX_TRANS_DATA) {
                        /*
                         * With non-extent format we are limited by the journal
                         * credit available.  Total credit needed to insert
                         * nrblocks contiguous blocks is dependent on the
                         * nrblocks.  So limit nrblocks.
                         */
                        goto flush_it;
                } else if ((nrblocks + (b_size >> mpd->inode->i_blkbits)) >
                                EXT4_MAX_TRANS_DATA) {
                        /*
                         * Adding the new buffer_head would make it cross the
                         * allowed limit for which we have journal credit
                         * reserved. So limit the new bh->b_size
                         */
                        b_size = (EXT4_MAX_TRANS_DATA - nrblocks) <<
                                                mpd->inode->i_blkbits;
                        /* we will do mpage_da_submit_io in the next loop */
                }
        }
        /*
         * First block in the extent
         */
        if (mpd->b_size == 0) {
                mpd->b_blocknr = logical;
                mpd->b_size = b_size;
                mpd->b_state = b_state & BH_FLAGS;
                return;
        }

        next = mpd->b_blocknr + nrblocks;
        /*
         * Can we merge the block to our big extent?
         */
        if (logical == next && (b_state & BH_FLAGS) == mpd->b_state) {
                mpd->b_size += b_size;
                return;
        }

flush_it:
        /*
         * We couldn't merge the block to our extent, so we
         * need to flush current  extent and start new one
         */
        mpage_da_map_and_submit(mpd);
        return;
}

static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh)
{
        return (buffer_delay(bh) || buffer_unwritten(bh)) && buffer_dirty(bh);
}

/*
 * This function is grabs code from the very beginning of
 * ext4_map_blocks, but assumes that the caller is from delayed write
 * time. This function looks up the requested blocks and sets the
 * buffer delay bit under the protection of i_data_sem.
 */
static int ext4_da_map_blocks(struct inode *inode, sector_t iblock,
                              struct ext4_map_blocks *map,
                              struct buffer_head *bh)
{
        int retval;
        sector_t invalid_block = ~((sector_t) 0xffff);

        if (invalid_block < ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es))
                invalid_block = ~0;

        map->m_flags = 0;
        ext_debug("ext4_da_map_blocks(): inode %lu, max_blocks %u,"
                  "logical block %lu\n", inode->i_ino, map->m_len,
                  (unsigned long) map->m_lblk);
        /*
         * Try to see if we can get the block without requesting a new
         * file system block.
         */
        down_read((&EXT4_I(inode)->i_data_sem));
        if (ext4_has_inline_data(inode)) {
                /*
                 * We will soon create blocks for this page, and let
                 * us pretend as if the blocks aren't allocated yet.
                 * In case of clusters, we have to handle the work
                 * of mapping from cluster so that the reserved space
                 * is calculated properly.
                 */
                if ((EXT4_SB(inode->i_sb)->s_cluster_ratio > 1) &&
                    ext4_find_delalloc_cluster(inode, map->m_lblk))
                        map->m_flags |= EXT4_MAP_FROM_CLUSTER;
                retval = 0;
        } else if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                retval = ext4_ext_map_blocks(NULL, inode, map, 0);
        else
                retval = ext4_ind_map_blocks(NULL, inode, map, 0);

        if (retval == 0) {
                /*
                 * XXX: __block_prepare_write() unmaps passed block,
                 * is it OK?
                 */
                /* If the block was allocated from previously allocated cluster,
                 * then we dont need to reserve it again. */
                if (!(map->m_flags & EXT4_MAP_FROM_CLUSTER)) {
                        retval = ext4_da_reserve_space(inode, iblock);
                        if (retval)
                                /* not enough space to reserve */
                                goto out_unlock;
                }

                retval = ext4_es_insert_extent(inode, map->m_lblk, map->m_len);
                if (retval)
                        goto out_unlock;

                /* Clear EXT4_MAP_FROM_CLUSTER flag since its purpose is served
                 * and it should not appear on the bh->b_state.
                 */
                map->m_flags &= ~EXT4_MAP_FROM_CLUSTER;

                map_bh(bh, inode->i_sb, invalid_block);
                set_buffer_new(bh);
                set_buffer_delay(bh);
        }

out_unlock:
        up_read((&EXT4_I(inode)->i_data_sem));

        return retval;
}

/*
 * This is a special get_blocks_t callback which is used by
 * ext4_da_write_begin().  It will either return mapped block or
 * reserve space for a single block.
 *
 * For delayed buffer_head we have BH_Mapped, BH_New, BH_Delay set.
 * We also have b_blocknr = -1 and b_bdev initialized properly
 *
 * For unwritten buffer_head we have BH_Mapped, BH_New, BH_Unwritten set.
 * We also have b_blocknr = physicalblock mapping unwritten extent and b_bdev
 * initialized properly.
 */
int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
                           struct buffer_head *bh, int create)
{
        struct ext4_map_blocks map;
        int ret = 0;

        BUG_ON(create == 0);
        BUG_ON(bh->b_size != inode->i_sb->s_blocksize);

        map.m_lblk = iblock;
        map.m_len = 1;

        /*
         * first, we need to know whether the block is allocated already
         * preallocated blocks are unmapped but should treated
         * the same as allocated blocks.
         */
        ret = ext4_da_map_blocks(inode, iblock, &map, bh);
        if (ret <= 0)
                return ret;

        map_bh(bh, inode->i_sb, map.m_pblk);
        bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;

        if (buffer_unwritten(bh)) {
                /* A delayed write to unwritten bh should be marked
                 * new and mapped.  Mapped ensures that we don't do
                 * get_block multiple times when we write to the same
                 * offset and new ensures that we do proper zero out
                 * for partial write.
                 */
                set_buffer_new(bh);
                set_buffer_mapped(bh);
        }
        return 0;
}

static int bget_one(handle_t *handle, struct buffer_head *bh)
{
        get_bh(bh);
        return 0;
}

static int bput_one(handle_t *handle, struct buffer_head *bh)
{
        put_bh(bh);
        return 0;
}

static int __ext4_journalled_writepage(struct page *page,
                                       unsigned int len)
{
        struct address_space *mapping = page->mapping;
        struct inode *inode = mapping->host;
        struct buffer_head *page_bufs = NULL;
        handle_t *handle = NULL;
        int ret = 0, err = 0;
        int inline_data = ext4_has_inline_data(inode);
        struct buffer_head *inode_bh = NULL;

        ClearPageChecked(page);

        if (inline_data) {
                BUG_ON(page->index != 0);
                BUG_ON(len > ext4_get_max_inline_size(inode));
                inode_bh = ext4_journalled_write_inline_data(inode, len, page);
                if (inode_bh == NULL)
                        goto out;
        } else {
                page_bufs = page_buffers(page);
                if (!page_bufs) {
                        BUG();
                        goto out;
                }
                ext4_walk_page_buffers(handle, page_bufs, 0, len,
                                       NULL, bget_one);
        }
        /* As soon as we unlock the page, it can go away, but we have
         * references to buffers so we are safe */
        unlock_page(page);

        handle = ext4_journal_start(inode, ext4_writepage_trans_blocks(inode));
        if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                goto out;
        }

        BUG_ON(!ext4_handle_valid(handle));

        if (inline_data) {
                ret = ext4_journal_get_write_access(handle, inode_bh);

                err = ext4_handle_dirty_metadata(handle, inode, inode_bh);

        } else {
                ret = ext4_walk_page_buffers(handle, page_bufs, 0, len, NULL,
                                             do_journal_get_write_access);

                err = ext4_walk_page_buffers(handle, page_bufs, 0, len, NULL,
                                             write_end_fn);
        }
        if (ret == 0)
                ret = err;
        EXT4_I(inode)->i_datasync_tid = handle->h_transaction->t_tid;
        err = ext4_journal_stop(handle);
        if (!ret)
                ret = err;

        if (!ext4_has_inline_data(inode))
                ext4_walk_page_buffers(handle, page_bufs, 0, len,
                                       NULL, bput_one);
        ext4_set_inode_state(inode, EXT4_STATE_JDATA);
out:
        brelse(inode_bh);
        return ret;
}

/*
 * Note that we don't need to start a transaction unless we're journaling data
 * because we should have holes filled from ext4_page_mkwrite(). We even don't
 * need to file the inode to the transaction's list in ordered mode because if
 * we are writing back data added by write(), the inode is already there and if
 * we are writing back data modified via mmap(), no one guarantees in which
 * transaction the data will hit the disk. In case we are journaling data, we
 * cannot start transaction directly because transaction start ranks above page
 * lock so we have to do some magic.
 *
 * This function can get called via...
 *   - ext4_da_writepages after taking page lock (have journal handle)
 *   - journal_submit_inode_data_buffers (no journal handle)
 *   - shrink_page_list via the kswapd/direct reclaim (no journal handle)
 *   - grab_page_cache when doing write_begin (have journal handle)
 *
 * We don't do any block allocation in this function. If we have page with
 * multiple blocks we need to write those buffer_heads that are mapped. This
 * is important for mmaped based write. So if we do with blocksize 1K
 * truncate(f, 1024);
 * a = mmap(f, 0, 4096);
 * a[0] = 'a';
 * truncate(f, 4096);
 * we have in the page first buffer_head mapped via page_mkwrite call back
 * but other buffer_heads would be unmapped but dirty (dirty done via the
 * do_wp_page). So writepage should write the first block. If we modify
 * the mmap area beyond 1024 we will again get a page_fault and the
 * page_mkwrite callback will do the block allocation and mark the
 * buffer_heads mapped.
 *
 * We redirty the page if we have any buffer_heads that is either delay or
 * unwritten in the page.
 *
 * We can get recursively called as show below.
 *
 *      ext4_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->
 *              ext4_writepage()
 *
 * But since we don't do any block allocation we should not deadlock.
 * Page also have the dirty flag cleared so we don't get recurive page_lock.
 */
static int ext4_writepage(struct page *page,
                          struct writeback_control *wbc)
{
        int ret = 0;
        loff_t size;
        unsigned int len;
        struct buffer_head *page_bufs = NULL;
        struct inode *inode = page->mapping->host;
        struct ext4_io_submit io_submit;

        trace_ext4_writepage(page);
        size = i_size_read(inode);
        if (page->index == size >> PAGE_CACHE_SHIFT)
                len = size & ~PAGE_CACHE_MASK;
        else
                len = PAGE_CACHE_SIZE;

        page_bufs = page_buffers(page);
        if (ext4_walk_page_buffers(NULL, page_bufs, 0, len, NULL,
                                   ext4_bh_delay_or_unwritten)) {
                /*
                 * We don't want to do block allocation, so redirty
                 * the page and return.  We may reach here when we do
                 * a journal commit via journal_submit_inode_data_buffers.
                 * We can also reach here via shrink_page_list but it
                 * should never be for direct reclaim so warn if that
                 * happens
                 */
                WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
                                                                PF_MEMALLOC);
                redirty_page_for_writepage(wbc, page);
                unlock_page(page);
                return 0;
        }

        if (PageChecked(page) && ext4_should_journal_data(inode))
                /*
                 * It's mmapped pagecache.  Add buffers and journal it.  There
                 * doesn't seem much point in redirtying the page here.
                 */
                return __ext4_journalled_writepage(page, len);

        memset(&io_submit, 0, sizeof(io_submit));
        ret = ext4_bio_write_page(&io_submit, page, len, wbc);
        ext4_io_submit(&io_submit);
        return ret;
}

/*
 * This is called via ext4_da_writepages() to
 * calculate the total number of credits to reserve to fit
 * a single extent allocation into a single transaction,
 * ext4_da_writpeages() will loop calling this before
 * the block allocation.
 */

static int ext4_da_writepages_trans_blocks(struct inode *inode)
{
        int max_blocks = EXT4_I(inode)->i_reserved_data_blocks;

        /*
         * With non-extent format the journal credit needed to
         * insert nrblocks contiguous block is dependent on
         * number of contiguous block. So we will limit
         * number of contiguous block to a sane value
         */
        if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) &&
            (max_blocks > EXT4_MAX_TRANS_DATA))
                max_blocks = EXT4_MAX_TRANS_DATA;

        return ext4_chunk_trans_blocks(inode, max_blocks);
}

/*
 * write_cache_pages_da - walk the list of dirty pages of the given
 * address space and accumulate pages that need writing, and call
 * mpage_da_map_and_submit to map a single contiguous memory region
 * and then write them.
 */
static int write_cache_pages_da(handle_t *handle,
                                struct address_space *mapping,
                                struct writeback_control *wbc,
                                struct mpage_da_data *mpd,
                                pgoff_t *done_index)
{
        struct buffer_head      *bh, *head;
        struct inode            *inode = mapping->host;
        struct pagevec          pvec;
        unsigned int            nr_pages;
        sector_t                logical;
        pgoff_t                 index, end;
        long                    nr_to_write = wbc->nr_to_write;
        int                     i, tag, ret = 0;

        memset(mpd, 0, sizeof(struct mpage_da_data));
        mpd->wbc = wbc;
        mpd->inode = inode;
        pagevec_init(&pvec, 0);
        index = wbc->range_start >> PAGE_CACHE_SHIFT;
        end = wbc->range_end >> PAGE_CACHE_SHIFT;

        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
                tag = PAGECACHE_TAG_TOWRITE;
        else
                tag = PAGECACHE_TAG_DIRTY;

        *done_index = index;
        while (index <= end) {
                nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
                              min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
                if (nr_pages == 0)
                        return 0;

                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];

                        /*
                         * At this point, the page may be truncated or
                         * invalidated (changing page->mapping to NULL), or
                         * even swizzled back from swapper_space to tmpfs file
                         * mapping. However, page->index will not change
                         * because we have a reference on the page.
                         */
                        if (page->index > end)
                                goto out;

                        *done_index = page->index + 1;

                        /*
                         * If we can't merge this page, and we have
                         * accumulated an contiguous region, write it
                         */
                        if ((mpd->next_page != page->index) &&
                            (mpd->next_page != mpd->first_page)) {
                                mpage_da_map_and_submit(mpd);
                                goto ret_extent_tail;
                        }

                        lock_page(page);

                        /*
                         * If the page is no longer dirty, or its
                         * mapping no longer corresponds to inode we
                         * are writing (which means it has been
                         * truncated or invalidated), or the page is
                         * already under writeback and we are not
                         * doing a data integrity writeback, skip the page
                         */
                        if (!PageDirty(page) ||
                            (PageWriteback(page) &&
                             (wbc->sync_mode == WB_SYNC_NONE)) ||
                            unlikely(page->mapping != mapping)) {
                                unlock_page(page);
                                continue;
                        }

                        wait_on_page_writeback(page);
                        BUG_ON(PageWriteback(page));

                        /*
                         * If we have inline data and arrive here, it means that
                         * we will soon create the block for the 1st page, so
                         * we'd better clear the inline data here.
                         */
                        if (ext4_has_inline_data(inode)) {
                                BUG_ON(ext4_test_inode_state(inode,
                                                EXT4_STATE_MAY_INLINE_DATA));
                                ext4_destroy_inline_data(handle, inode);
                        }

                        if (mpd->next_page != page->index)
                                mpd->first_page = page->index;
                        mpd->next_page = page->index + 1;
                        logical = (sector_t) page->index <<
                                (PAGE_CACHE_SHIFT - inode->i_blkbits);

                        /* Add all dirty buffers to mpd */
                        head = page_buffers(page);
                        bh = head;
                        do {
                                BUG_ON(buffer_locked(bh));
                                /*
                                 * We need to try to allocate unmapped blocks
                                 * in the same page.  Otherwise we won't make
                                 * progress with the page in ext4_writepage
                                 */
                                if (ext4_bh_delay_or_unwritten(NULL, bh)) {
                                        mpage_add_bh_to_extent(mpd, logical,
                                                               bh->b_size,
                                                               bh->b_state);
                                        if (mpd->io_done)
                                                goto ret_extent_tail;
                                } else if (buffer_dirty(bh) &&
                                           buffer_mapped(bh)) {
                                        /*
                                         * mapped dirty buffer. We need to
                                         * update the b_state because we look
                                         * at b_state in mpage_da_map_blocks.
                                         * We don't update b_size because if we
                                         * find an unmapped buffer_head later
                                         * we need to use the b_state flag of
                                         * that buffer_head.
                                         */
                                        if (mpd->b_size == 0)
                                                mpd->b_state =
                                                        bh->b_state & BH_FLAGS;
                                }
                                logical++;
                        } while ((bh = bh->b_this_page) != head);

                        if (nr_to_write > 0) {
                                nr_to_write--;
                                if (nr_to_write == 0 &&
                                    wbc->sync_mode == WB_SYNC_NONE)
                                        /*
                                         * We stop writing back only if we are
                                         * not doing integrity sync. In case of
                                         * integrity sync we have to keep going
                                         * because someone may be concurrently
                                         * dirtying pages, and we might have
                                         * synced a lot of newly appeared dirty
                                         * pages, but have not synced all of the
                                         * old dirty pages.
                                         */
                                        goto out;
                        }
                }
                pagevec_release(&pvec);
                cond_resched();
        }
        return 0;
ret_extent_tail:
        ret = MPAGE_DA_EXTENT_TAIL;
out:
        pagevec_release(&pvec);
        cond_resched();
        return ret;
}


static int ext4_da_writepages(struct address_space *mapping,
                              struct writeback_control *wbc)
{
        pgoff_t index;
        int range_whole = 0;
        handle_t *handle = NULL;
        struct mpage_da_data mpd;
        struct inode *inode = mapping->host;
        int pages_written = 0;
        unsigned int max_pages;
        int range_cyclic, cycled = 1, io_done = 0;
        int needed_blocks, ret = 0;
        long desired_nr_to_write, nr_to_writebump = 0;
        loff_t range_start = wbc->range_start;
        struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
        pgoff_t done_index = 0;
        pgoff_t end;
        struct blk_plug plug;

        trace_ext4_da_writepages(inode, wbc);

        /*
         * No pages to write? This is mainly a kludge to avoid starting
         * a transaction for special inodes like journal inode on last iput()
         * because that could violate lock ordering on umount
         */
        if (!mapping->nrpages || !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
                return 0;

        /*
         * If the filesystem has aborted, it is read-only, so return
         * right away instead of dumping stack traces later on that
         * will obscure the real source of the problem.  We test
         * EXT4_MF_FS_ABORTED instead of sb->s_flag's MS_RDONLY because
         * the latter could be true if the filesystem is mounted
         * read-only, and in that case, ext4_da_writepages should
         * *never* be called, so if that ever happens, we would want
         * the stack trace.
         */
        if (unlikely(sbi->s_mount_flags & EXT4_MF_FS_ABORTED))
                return -EROFS;

        if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
                range_whole = 1;

        range_cyclic = wbc->range_cyclic;
        if (wbc->range_cyclic) {
                index = mapping->writeback_index;
                if (index)
                        cycled = 0;
                wbc->range_start = index << PAGE_CACHE_SHIFT;
                wbc->range_end  = LLONG_MAX;
                wbc->range_cyclic = 0;
                end = -1;
        } else {
                index = wbc->range_start >> PAGE_CACHE_SHIFT;
                end = wbc->range_end >> PAGE_CACHE_SHIFT;
        }

        /*
         * This works around two forms of stupidity.  The first is in
         * the writeback code, which caps the maximum number of pages
         * written to be 1024 pages.  This is wrong on multiple
         * levels; different architectues have a different page size,
         * which changes the maximum amount of data which gets
         * written.  Secondly, 4 megabytes is way too small.  XFS
         * forces this value to be 16 megabytes by multiplying
         * nr_to_write parameter by four, and then relies on its
         * allocator to allocate larger extents to make them
         * contiguous.  Unfortunately this brings us to the second
         * stupidity, which is that ext4's mballoc code only allocates
         * at most 2048 blocks.  So we force contiguous writes up to
         * the number of dirty blocks in the inode, or
         * sbi->max_writeback_mb_bump whichever is smaller.
         */
        max_pages = sbi->s_max_writeback_mb_bump << (20 - PAGE_CACHE_SHIFT);
        if (!range_cyclic && range_whole) {
                if (wbc->nr_to_write == LONG_MAX)
                        desired_nr_to_write = wbc->nr_to_write;
                else
                        desired_nr_to_write = wbc->nr_to_write * 8;
        } else
                desired_nr_to_write = ext4_num_dirty_pages(inode, index,
                                                           max_pages);
        if (desired_nr_to_write > max_pages)
                desired_nr_to_write = max_pages;

        if (wbc->nr_to_write < desired_nr_to_write) {
                nr_to_writebump = desired_nr_to_write - wbc->nr_to_write;
                wbc->nr_to_write = desired_nr_to_write;
        }

retry:
        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
                tag_pages_for_writeback(mapping, index, end);

        blk_start_plug(&plug);
        while (!ret && wbc->nr_to_write > 0) {

                /*
                 * we  insert one extent at a time. So we need
                 * credit needed for single extent allocation.
                 * journalled mode is currently not supported
                 * by delalloc
                 */
                BUG_ON(ext4_should_journal_data(inode));
                needed_blocks = ext4_da_writepages_trans_blocks(inode);

                /* start a new transaction*/
                handle = ext4_journal_start(inode, needed_blocks);
                if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        ext4_msg(inode->i_sb, KERN_CRIT, "%s: jbd2_start: "
                               "%ld pages, ino %lu; err %d", __func__,
                                wbc->nr_to_write, inode->i_ino, ret);
                        blk_finish_plug(&plug);
                        goto out_writepages;
                }

                /*
                 * Now call write_cache_pages_da() to find the next
                 * contiguous region of logical blocks that need
                 * blocks to be allocated by ext4 and submit them.
                 */
                ret = write_cache_pages_da(handle, mapping,
                                           wbc, &mpd, &done_index);
                /*
                 * If we have a contiguous extent of pages and we
                 * haven't done the I/O yet, map the blocks and submit
                 * them for I/O.
                 */
                if (!mpd.io_done && mpd.next_page != mpd.first_page) {
                        mpage_da_map_and_submit(&mpd);
                        ret = MPAGE_DA_EXTENT_TAIL;
                }
                trace_ext4_da_write_pages(inode, &mpd);
                wbc->nr_to_write -= mpd.pages_written;

                ext4_journal_stop(handle);

                if ((mpd.retval == -ENOSPC) && sbi->s_journal) {
                        /* commit the transaction which would
                         * free blocks released in the transaction
                         * and try again
                         */
                        jbd2_journal_force_commit_nested(sbi->s_journal);
                        ret = 0;
                } else if (ret == MPAGE_DA_EXTENT_TAIL) {
                        /*
                         * Got one extent now try with rest of the pages.
                         * If mpd.retval is set -EIO, journal is aborted.
                         * So we don't need to write any more.
                         */
                        pages_written += mpd.pages_written;
                        ret = mpd.retval;
                        io_done = 1;
                } else if (wbc->nr_to_write)
                        /*
                         * There is no more writeout needed
                         * or we requested for a noblocking writeout
                         * and we found the device congested
                         */
                        break;
        }
        blk_finish_plug(&plug);
        if (!io_done && !cycled) {
                cycled = 1;
                index = 0;
                wbc->range_start = index << PAGE_CACHE_SHIFT;
                wbc->range_end  = mapping->writeback_index - 1;
                goto retry;
        }

        /* Update index */
        wbc->range_cyclic = range_cyclic;
        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
                /*
                 * set the writeback_index so that range_cyclic
                 * mode will write it back later
                 */
                mapping->writeback_index = done_index;

out_writepages:
        wbc->nr_to_write -= nr_to_writebump;
        wbc->range_start = range_start;
        trace_ext4_da_writepages_result(inode, wbc, ret, pages_written);
        return ret;
}

static int ext4_nonda_switch(struct super_block *sb)
{
        s64 free_blocks, dirty_blocks;
        struct ext4_sb_info *sbi = EXT4_SB(sb);

        /*
         * switch to non delalloc mode if we are running low
         * on free block. The free block accounting via percpu
         * counters can get slightly wrong with percpu_counter_batch getting
         * accumulated on each CPU without updating global counters
         * Delalloc need an accurate free block accounting. So switch
         * to non delalloc when we are near to error range.
         */
        free_blocks  = EXT4_C2B(sbi,
                percpu_counter_read_positive(&sbi->s_freeclusters_counter));
        dirty_blocks = percpu_counter_read_positive(&sbi->s_dirtyclusters_counter);
        /*
         * Start pushing delalloc when 1/2 of free blocks are dirty.
         */
        if (dirty_blocks && (free_blocks < 2 * dirty_blocks) &&
            !writeback_in_progress(sb->s_bdi) &&
            down_read_trylock(&sb->s_umount)) {
                writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);
                up_read(&sb->s_umount);
        }

        if (2 * free_blocks < 3 * dirty_blocks ||
                free_blocks < (dirty_blocks + EXT4_FREECLUSTERS_WATERMARK)) {
                /*
                 * free block count is less than 150% of dirty blocks
                 * or free blocks is less than watermark
                 */
                return 1;
        }
        return 0;
}

static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
                               loff_t pos, unsigned len, unsigned flags,
                               struct page **pagep, void **fsdata)
{
        int ret, retries = 0;
        struct page *page;
        pgoff_t index;
        struct inode *inode = mapping->host;
        handle_t *handle;

        index = pos >> PAGE_CACHE_SHIFT;

        if (ext4_nonda_switch(inode->i_sb)) {
                *fsdata = (void *)FALL_BACK_TO_NONDELALLOC;
                return ext4_write_begin(file, mapping, pos,
                                        len, flags, pagep, fsdata);
        }
        *fsdata = (void *)0;
        trace_ext4_da_write_begin(inode, pos, len, flags);

        if (ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)) {
                ret = ext4_da_write_inline_data_begin(mapping, inode,
                                                      pos, len, flags,
                                                      pagep, fsdata);
                if (ret < 0)
                        goto out;
                if (ret == 1) {
                        ret = 0;
                        goto out;
                }
        }

retry:
        /*
         * With delayed allocation, we don't log the i_disksize update
         * if there is delayed block allocation. But we still need
         * to journalling the i_disksize update if writes to the end
         * of file which has an already mapped buffer.
         */
        handle = ext4_journal_start(inode, 1);
        if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                goto out;
        }
        /* We cannot recurse into the filesystem as the transaction is already
         * started */
        flags |= AOP_FLAG_NOFS;

        page = grab_cache_page_write_begin(mapping, index, flags);
        if (!page) {
                ext4_journal_stop(handle);
                ret = -ENOMEM;
                goto out;
        }
        *pagep = page;

        ret = __block_write_begin(page, pos, len, ext4_da_get_block_prep);
        if (ret < 0) {
                unlock_page(page);
                ext4_journal_stop(handle);
                page_cache_release(page);
                /*
                 * block_write_begin may have instantiated a few blocks
                 * outside i_size.  Trim these off again. Don't need
                 * i_size_read because we hold i_mutex.
                 */
                if (pos + len > inode->i_size)
                        ext4_truncate_failed_write(inode);
        }

        if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
                goto retry;
out:
        return ret;
}

/*
 * Check if we should update i_disksize
 * when write to the end of file but not require block allocation
 */
static int ext4_da_should_update_i_disksize(struct page *page,
                                            unsigned long offset)
{
        struct buffer_head *bh;
        struct inode *inode = page->mapping->host;
        unsigned int idx;
        int i;

        bh = page_buffers(page);
        idx = offset >> inode->i_blkbits;

        for (i = 0; i < idx; i++)
                bh = bh->b_this_page;

        if (!buffer_mapped(bh) || (buffer_delay(bh)) || buffer_unwritten(bh))
                return 0;
        return 1;
}

static int ext4_da_write_end(struct file *file,
                             struct address_space *mapping,
                             loff_t pos, unsigned len, unsigned copied,
                             struct page *page, void *fsdata)
{
        struct inode *inode = mapping->host;
        int ret = 0, ret2;
        handle_t *handle = ext4_journal_current_handle();
        loff_t new_i_size;
        unsigned long start, end;
        int write_mode = (int)(unsigned long)fsdata;

        if (write_mode == FALL_BACK_TO_NONDELALLOC) {
                switch (ext4_inode_journal_mode(inode)) {
                case EXT4_INODE_ORDERED_DATA_MODE:
                        return ext4_ordered_write_end(file, mapping, pos,
                                        len, copied, page, fsdata);
                case EXT4_INODE_WRITEBACK_DATA_MODE:
                        return ext4_writeback_write_end(file, mapping, pos,
                                        len, copied, page, fsdata);
                default:
                        BUG();
                }
        }

        trace_ext4_da_write_end(inode, pos, len, copied);
        start = pos & (PAGE_CACHE_SIZE - 1);
        end = start + copied - 1;

        /*
         * generic_write_end() will run mark_inode_dirty() if i_size
         * changes.  So let's piggyback the i_disksize mark_inode_dirty
         * into that.
         */
        new_i_size = pos + copied;
        if (copied && new_i_size > EXT4_I(inode)->i_disksize) {
                if (ext4_has_inline_data(inode) ||
                    ext4_da_should_update_i_disksize(page, end)) {
                        down_write(&EXT4_I(inode)->i_data_sem);
                        if (new_i_size > EXT4_I(inode)->i_disksize)
                                EXT4_I(inode)->i_disksize = new_i_size;
                        up_write(&EXT4_I(inode)->i_data_sem);
                        /* We need to mark inode dirty even if
                         * new_i_size is less that inode->i_size
                         * bu greater than i_disksize.(hint delalloc)
                         */
                        ext4_mark_inode_dirty(handle, inode);
                }
        }

        if (write_mode != CONVERT_INLINE_DATA &&
            ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA) &&
            ext4_has_inline_data(inode))
                ret2 = ext4_da_write_inline_data_end(inode, pos, len, copied,
                                                     page);
        else
                ret2 = generic_write_end(file, mapping, pos, len, copied,
                                                        page, fsdata);

        copied = ret2;
        if (ret2 < 0)
                ret = ret2;
        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;

        return ret ? ret : copied;
}

static void ext4_da_invalidatepage(struct page *page, unsigned long offset)
{
        /*
         * Drop reserved blocks
         */
        BUG_ON(!PageLocked(page));
        if (!page_has_buffers(page))
                goto out;

        ext4_da_page_release_reservation(page, offset);

out:
        ext4_invalidatepage(page, offset);

        return;
}

/*
 * Force all delayed allocation blocks to be allocated for a given inode.
 */
int ext4_alloc_da_blocks(struct inode *inode)
{
        trace_ext4_alloc_da_blocks(inode);

        if (!EXT4_I(inode)->i_reserved_data_blocks &&
            !EXT4_I(inode)->i_reserved_meta_blocks)
                return 0;

        /*
         * We do something simple for now.  The filemap_flush() will
         * also start triggering a write of the data blocks, which is
         * not strictly speaking necessary (and for users of
         * laptop_mode, not even desirable).  However, to do otherwise
         * would require replicating code paths in:
         *
         * ext4_da_writepages() ->
         *    write_cache_pages() ---> (via passed in callback function)
         *        __mpage_da_writepage() -->
         *           mpage_add_bh_to_extent()
         *           mpage_da_map_blocks()
         *
         * The problem is that write_cache_pages(), located in
         * mm/page-writeback.c, marks pages clean in preparation for
         * doing I/O, which is not desirable if we're not planning on
         * doing I/O at all.
         *
         * We could call write_cache_pages(), and then redirty all of
         * the pages by calling redirty_page_for_writepage() but that
         * would be ugly in the extreme.  So instead we would need to
         * replicate parts of the code in the above functions,
         * simplifying them because we wouldn't actually intend to
         * write out the pages, but rather only collect contiguous
         * logical block extents, call the multi-block allocator, and
         * then update the buffer heads with the block allocations.
         *
         * For now, though, we'll cheat by calling filemap_flush(),
         * which will map the blocks, and start the I/O, but not
         * actually wait for the I/O to complete.
         */
        return filemap_flush(inode->i_mapping);
}

/*
 * bmap() is special.  It gets used by applications such as lilo and by
 * the swapper to find the on-disk block of a specific piece of data.
 *
 * Naturally, this is dangerous if the block concerned is still in the
 * journal.  If somebody makes a swapfile on an ext4 data-journaling
 * filesystem and enables swap, then they may get a nasty shock when the
 * data getting swapped to that swapfile suddenly gets overwritten by
 * the original zero's written out previously to the journal and
 * awaiting writeback in the kernel's buffer cache.
 *
 * So, if we see any bmap calls here on a modified, data-journaled file,
 * take extra steps to flush any blocks which might be in the cache.
 */
static sector_t ext4_bmap(struct address_space *mapping, sector_t block)
{
        struct inode *inode = mapping->host;
        journal_t *journal;
        int err;

        /*
         * We can get here for an inline file via the FIBMAP ioctl
         */
        if (ext4_has_inline_data(inode))
                return 0;

        if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
                        test_opt(inode->i_sb, DELALLOC)) {
                /*
                 * With delalloc we want to sync the file
                 * so that we can make sure we allocate
                 * blocks for file
                 */
                filemap_write_and_wait(mapping);
        }

        if (EXT4_JOURNAL(inode) &&
            ext4_test_inode_state(inode, EXT4_STATE_JDATA)) {
                /*
                 * This is a REALLY heavyweight approach, but the use of
                 * bmap on dirty files is expected to be extremely rare:
                 * only if we run lilo or swapon on a freshly made file
                 * do we expect this to happen.
                 *
                 * (bmap requires CAP_SYS_RAWIO so this does not
                 * represent an unprivileged user DOS attack --- we'd be
                 * in trouble if mortal users could trigger this path at
                 * will.)
                 *
                 * NB. EXT4_STATE_JDATA is not set on files other than
                 * regular files.  If somebody wants to bmap a directory
                 * or symlink and gets confused because the buffer
                 * hasn't yet been flushed to disk, they deserve
                 * everything they get.
                 */

                ext4_clear_inode_state(inode, EXT4_STATE_JDATA);
                journal = EXT4_JOURNAL(inode);
                jbd2_journal_lock_updates(journal);
                err = jbd2_journal_flush(journal);
                jbd2_journal_unlock_updates(journal);

                if (err)
                        return 0;
        }

        return generic_block_bmap(mapping, block, ext4_get_block);
}

static int ext4_readpage(struct file *file, struct page *page)
{
        int ret = -EAGAIN;
        struct inode *inode = page->mapping->host;

        trace_ext4_readpage(page);

        if (ext4_has_inline_data(inode))
                ret = ext4_readpage_inline(inode, page);

        if (ret == -EAGAIN)
                return mpage_readpage(page, ext4_get_block);

        return ret;
}

static int
ext4_readpages(struct file *file, struct address_space *mapping,
                struct list_head *pages, unsigned nr_pages)
{
        struct inode *inode = mapping->host;

        /* If the file has inline data, no need to do readpages. */
        if (ext4_has_inline_data(inode))
                return 0;

        return mpage_readpages(mapping, pages, nr_pages, ext4_get_block);
}

static void ext4_invalidatepage(struct page *page, unsigned long offset)
{
        trace_ext4_invalidatepage(page, offset);

        /* No journalling happens on data buffers when this function is used */
        WARN_ON(page_has_buffers(page) && buffer_jbd(page_buffers(page)));

        block_invalidatepage(page, offset);
}

static int __ext4_journalled_invalidatepage(struct page *page,
                                            unsigned long offset)
{
        journal_t *journal = EXT4_JOURNAL(page->mapping->host);

        trace_ext4_journalled_invalidatepage(page, offset);

        /*
         * If it's a full truncate we just forget about the pending dirtying
         */
        if (offset == 0)
                ClearPageChecked(page);

        return jbd2_journal_invalidatepage(journal, page, offset);
}

/* Wrapper for aops... */
static void ext4_journalled_invalidatepage(struct page *page,
                                           unsigned long offset)
{
        WARN_ON(__ext4_journalled_invalidatepage(page, offset) < 0);
}

static int ext4_releasepage(struct page *page, gfp_t wait)
{
        journal_t *journal = EXT4_JOURNAL(page->mapping->host);

        trace_ext4_releasepage(page);

        WARN_ON(PageChecked(page));
        if (!page_has_buffers(page))
                return 0;
        if (journal)
                return jbd2_journal_try_to_free_buffers(journal, page, wait);
        else
                return try_to_free_buffers(page);
}

/*
 * ext4_get_block used when preparing for a DIO write or buffer write.
 * We allocate an uinitialized extent if blocks haven't been allocated.
 * The extent will be converted to initialized after the IO is complete.
 */
int ext4_get_block_write(struct inode *inode, sector_t iblock,
                   struct buffer_head *bh_result, int create)
{
        ext4_debug("ext4_get_block_write: inode %lu, create flag %d\n",
                   inode->i_ino, create);
        return _ext4_get_block(inode, iblock, bh_result,
                               EXT4_GET_BLOCKS_IO_CREATE_EXT);
}

static int ext4_get_block_write_nolock(struct inode *inode, sector_t iblock,
                   struct buffer_head *bh_result, int create)
{
        ext4_debug("ext4_get_block_write_nolock: inode %lu, create flag %d\n",
                   inode->i_ino, create);
        return _ext4_get_block(inode, iblock, bh_result,
                               EXT4_GET_BLOCKS_NO_LOCK);
}

static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
                            ssize_t size, void *private, int ret,
                            bool is_async)
{
        struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode;
        ext4_io_end_t *io_end = iocb->private;

        /* if not async direct IO or dio with 0 bytes write, just return */
        if (!io_end || !size)
                goto out;

        ext_debug("ext4_end_io_dio(): io_end 0x%p "
                  "for inode %lu, iocb 0x%p, offset %llu, size %zd\n",
                  iocb->private, io_end->inode->i_ino, iocb, offset,
                  size);

        iocb->private = NULL;

        /* if not aio dio with unwritten extents, just free io and return */
        if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
                ext4_free_io_end(io_end);
out:
                if (is_async)
                        aio_complete(iocb, ret, 0);
                inode_dio_done(inode);
                return;
        }

        io_end->offset = offset;
        io_end->size = size;
        if (is_async) {
                io_end->iocb = iocb;
                io_end->result = ret;
        }

        ext4_add_complete_io(io_end);
}

/*
 * For ext4 extent files, ext4 will do direct-io write to holes,
 * preallocated extents, and those write extend the file, no need to
 * fall back to buffered IO.
 *
 * For holes, we fallocate those blocks, mark them as uninitialized
 * If those blocks were preallocated, we mark sure they are split, but
 * still keep the range to write as uninitialized.
 *
 * The unwritten extents will be converted to written when DIO is completed.
 * For async direct IO, since the IO may still pending when return, we
 * set up an end_io call back function, which will do the conversion
 * when async direct IO completed.
 *
 * If the O_DIRECT write will extend the file then add this inode to the
 * orphan list.  So recovery will truncate it back to the original size
 * if the machine crashes during the write.
 *
 */
static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
                              const struct iovec *iov, loff_t offset,
                              unsigned long nr_segs)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file->f_mapping->host;
        ssize_t ret;
        size_t count = iov_length(iov, nr_segs);
        int overwrite = 0;
        get_block_t *get_block_func = NULL;
        int dio_flags = 0;
        loff_t final_size = offset + count;

        /* Use the old path for reads and writes beyond i_size. */
        if (rw != WRITE || final_size > inode->i_size)
                return ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs);

        BUG_ON(iocb->private == NULL);

        /* If we do a overwrite dio, i_mutex locking can be released */
        overwrite = *((int *)iocb->private);

        if (overwrite) {
                atomic_inc(&inode->i_dio_count);
                down_read(&EXT4_I(inode)->i_data_sem);
                mutex_unlock(&inode->i_mutex);
        }

        /*
         * We could direct write to holes and fallocate.
         *
         * Allocated blocks to fill the hole are marked as
         * uninitialized to prevent parallel buffered read to expose
         * the stale data before DIO complete the data IO.
         *
         * As to previously fallocated extents, ext4 get_block will
         * just simply mark the buffer mapped but still keep the
         * extents uninitialized.
         *
         * For non AIO case, we will convert those unwritten extents
         * to written after return back from blockdev_direct_IO.
         *
         * For async DIO, the conversion needs to be deferred when the
         * IO is completed. The ext4 end_io callback function will be
         * called to take care of the conversion work.  Here for async
         * case, we allocate an io_end structure to hook to the iocb.
         */
        iocb->private = NULL;
        ext4_inode_aio_set(inode, NULL);
        if (!is_sync_kiocb(iocb)) {
                ext4_io_end_t *io_end = ext4_init_io_end(inode, GFP_NOFS);
                if (!io_end) {
                        ret = -ENOMEM;
                        goto retake_lock;
                }
                io_end->flag |= EXT4_IO_END_DIRECT;
                iocb->private = io_end;
                /*
                 * we save the io structure for current async direct
                 * IO, so that later ext4_map_blocks() could flag the
                 * io structure whether there is a unwritten extents
                 * needs to be converted when IO is completed.
                 */
                ext4_inode_aio_set(inode, io_end);
        }

        if (overwrite) {
                get_block_func = ext4_get_block_write_nolock;
        } else {
                get_block_func = ext4_get_block_write;
                dio_flags = DIO_LOCKING;
        }
        ret = __blockdev_direct_IO(rw, iocb, inode,
                                   inode->i_sb->s_bdev, iov,
                                   offset, nr_segs,
                                   get_block_func,
                                   ext4_end_io_dio,
                                   NULL,
                                   dio_flags);

        if (iocb->private)
                ext4_inode_aio_set(inode, NULL);
        /*
         * The io_end structure takes a reference to the inode, that
         * structure needs to be destroyed and the reference to the
         * inode need to be dropped, when IO is complete, even with 0
         * byte write, or failed.
         *
         * In the successful AIO DIO case, the io_end structure will
         * be destroyed and the reference to the inode will be dropped
         * after the end_io call back function is called.
         *
         * In the case there is 0 byte write, or error case, since VFS
         * direct IO won't invoke the end_io call back function, we
         * need to free the end_io structure here.
         */
        if (ret != -EIOCBQUEUED && ret <= 0 && iocb->private) {
                ext4_free_io_end(iocb->private);
                iocb->private = NULL;
        } else if (ret > 0 && !overwrite && ext4_test_inode_state(inode,
                                                EXT4_STATE_DIO_UNWRITTEN)) {
                int err;
                /*
                 * for non AIO case, since the IO is already
                 * completed, we could do the conversion right here
                 */
                err = ext4_convert_unwritten_extents(inode,
                                                     offset, ret);
                if (err < 0)
                        ret = err;
                ext4_clear_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
        }

retake_lock:
        /* take i_mutex locking again if we do a ovewrite dio */
        if (overwrite) {
                inode_dio_done(inode);
                up_read(&EXT4_I(inode)->i_data_sem);
                mutex_lock(&inode->i_mutex);
        }

        return ret;
}

static ssize_t ext4_direct_IO(int rw, struct kiocb *iocb,
                              const struct iovec *iov, loff_t offset,
                              unsigned long nr_segs)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file->f_mapping->host;
        ssize_t ret;

        /*
         * If we are doing data journalling we don't support O_DIRECT
         */
        if (ext4_should_journal_data(inode))
                return 0;

        /* Let buffer I/O handle the inline data case. */
        if (ext4_has_inline_data(inode))
                return 0;

        trace_ext4_direct_IO_enter(inode, offset, iov_length(iov, nr_segs), rw);
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                ret = ext4_ext_direct_IO(rw, iocb, iov, offset, nr_segs);
        else
                ret = ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs);
        trace_ext4_direct_IO_exit(inode, offset,
                                iov_length(iov, nr_segs), rw, ret);
        return ret;
}

/*
 * Pages can be marked dirty completely asynchronously from ext4's journalling
 * activity.  By filemap_sync_pte(), try_to_unmap_one(), etc.  We cannot do
 * much here because ->set_page_dirty is called under VFS locks.  The page is
 * not necessarily locked.
 *
 * We cannot just dirty the page and leave attached buffers clean, because the
 * buffers' dirty state is "definitive".  We cannot just set the buffers dirty
 * or jbddirty because all the journalling code will explode.
 *
 * So what we do is to mark the page "pending dirty" and next time writepage
 * is called, propagate that into the buffers appropriately.
 */
static int ext4_journalled_set_page_dirty(struct page *page)
{
        SetPageChecked(page);
        return __set_page_dirty_nobuffers(page);
}

static const struct address_space_operations ext4_ordered_aops = {
        .readpage               = ext4_readpage,
        .readpages              = ext4_readpages,
        .writepage              = ext4_writepage,
        .write_begin            = ext4_write_begin,
        .write_end              = ext4_ordered_write_end,
        .bmap                   = ext4_bmap,
        .invalidatepage         = ext4_invalidatepage,
        .releasepage            = ext4_releasepage,
        .direct_IO              = ext4_direct_IO,
        .migratepage            = buffer_migrate_page,
        .is_partially_uptodate  = block_is_partially_uptodate,
        .error_remove_page      = generic_error_remove_page,
};

static const struct address_space_operations ext4_writeback_aops = {
        .readpage               = ext4_readpage,
        .readpages              = ext4_readpages,
        .writepage              = ext4_writepage,
        .write_begin            = ext4_write_begin,
        .write_end              = ext4_writeback_write_end,
        .bmap                   = ext4_bmap,
        .invalidatepage         = ext4_invalidatepage,
        .releasepage            = ext4_releasepage,
        .direct_IO              = ext4_direct_IO,
        .migratepage            = buffer_migrate_page,
        .is_partially_uptodate  = block_is_partially_uptodate,
        .error_remove_page      = generic_error_remove_page,
};

static const struct address_space_operations ext4_journalled_aops = {
        .readpage               = ext4_readpage,
        .readpages              = ext4_readpages,
        .writepage              = ext4_writepage,
        .write_begin            = ext4_write_begin,
        .write_end              = ext4_journalled_write_end,
        .set_page_dirty         = ext4_journalled_set_page_dirty,
        .bmap                   = ext4_bmap,
        .invalidatepage         = ext4_journalled_invalidatepage,
        .releasepage            = ext4_releasepage,
        .direct_IO              = ext4_direct_IO,
        .is_partially_uptodate  = block_is_partially_uptodate,
        .error_remove_page      = generic_error_remove_page,
};

static const struct address_space_operations ext4_da_aops = {
        .readpage               = ext4_readpage,
        .readpages              = ext4_readpages,
        .writepage              = ext4_writepage,
        .writepages             = ext4_da_writepages,
        .write_begin            = ext4_da_write_begin,
        .write_end              = ext4_da_write_end,
        .bmap                   = ext4_bmap,
        .invalidatepage         = ext4_da_invalidatepage,
        .releasepage            = ext4_releasepage,
        .direct_IO              = ext4_direct_IO,
        .migratepage            = buffer_migrate_page,
        .is_partially_uptodate  = block_is_partially_uptodate,
        .error_remove_page      = generic_error_remove_page,
};

void ext4_set_aops(struct inode *inode)
{
        switch (ext4_inode_journal_mode(inode)) {
        case EXT4_INODE_ORDERED_DATA_MODE:
                if (test_opt(inode->i_sb, DELALLOC))
                        inode->i_mapping->a_ops = &ext4_da_aops;
                else
                        inode->i_mapping->a_ops = &ext4_ordered_aops;
                break;
        case EXT4_INODE_WRITEBACK_DATA_MODE:
                if (test_opt(inode->i_sb, DELALLOC))
                        inode->i_mapping->a_ops = &ext4_da_aops;
                else
                        inode->i_mapping->a_ops = &ext4_writeback_aops;
                break;
        case EXT4_INODE_JOURNAL_DATA_MODE:
                inode->i_mapping->a_ops = &ext4_journalled_aops;
                break;
        default:
                BUG();
        }
}


/*
 * ext4_discard_partial_page_buffers()
 * Wrapper function for ext4_discard_partial_page_buffers_no_lock.
 * This function finds and locks the page containing the offset
 * "from" and passes it to ext4_discard_partial_page_buffers_no_lock.
 * Calling functions that already have the page locked should call
 * ext4_discard_partial_page_buffers_no_lock directly.
 */
int ext4_discard_partial_page_buffers(handle_t *handle,
                struct address_space *mapping, loff_t from,
                loff_t length, int flags)
{
        struct inode *inode = mapping->host;
        struct page *page;
        int err = 0;

        page = find_or_create_page(mapping, from >> PAGE_CACHE_SHIFT,
                                   mapping_gfp_mask(mapping) & ~__GFP_FS);
        if (!page)
                return -ENOMEM;

        err = ext4_discard_partial_page_buffers_no_lock(handle, inode, page,
                from, length, flags);

        unlock_page(page);
        page_cache_release(page);
        return err;
}

/*
 * ext4_discard_partial_page_buffers_no_lock()
 * Zeros a page range of length 'length' starting from offset 'from'.
 * Buffer heads that correspond to the block aligned regions of the
 * zeroed range will be unmapped.  Unblock aligned regions
 * will have the corresponding buffer head mapped if needed so that
 * that region of the page can be updated with the partial zero out.
 *
 * This function assumes that the page has already been  locked.  The
 * The range to be discarded must be contained with in the given page.
 * If the specified range exceeds the end of the page it will be shortened
 * to the end of the page that corresponds to 'from'.  This function is
 * appropriate for updating a page and it buffer heads to be unmapped and
 * zeroed for blocks that have been either released, or are going to be
 * released.
 *
 * handle: The journal handle
 * inode:  The files inode
 * page:   A locked page that contains the offset "from"
 * from:   The starting byte offset (from the beginning of the file)
 *         to begin discarding
 * len:    The length of bytes to discard
 * flags:  Optional flags that may be used:
 *
 *         EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED
 *         Only zero the regions of the page whose buffer heads
 *         have already been unmapped.  This flag is appropriate
 *         for updating the contents of a page whose blocks may
 *         have already been released, and we only want to zero
 *         out the regions that correspond to those released blocks.
 *
 * Returns zero on success or negative on failure.
 */
static int ext4_discard_partial_page_buffers_no_lock(handle_t *handle,
                struct inode *inode, struct page *page, loff_t from,
                loff_t length, int flags)
{
        ext4_fsblk_t index = from >> PAGE_CACHE_SHIFT;
        unsigned int offset = from & (PAGE_CACHE_SIZE-1);
        unsigned int blocksize, max, pos;
        ext4_lblk_t iblock;
        struct buffer_head *bh;
        int err = 0;

        blocksize = inode->i_sb->s_blocksize;
        max = PAGE_CACHE_SIZE - offset;

        if (index != page->index)
                return -EINVAL;

        /*
         * correct length if it does not fall between
         * 'from' and the end of the page
         */
        if (length > max || length < 0)
                length = max;

        iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);

        if (!page_has_buffers(page))
                create_empty_buffers(page, blocksize, 0);

        /* Find the buffer that contains "offset" */
        bh = page_buffers(page);
        pos = blocksize;
        while (offset >= pos) {
                bh = bh->b_this_page;
                iblock++;
                pos += blocksize;
        }

        pos = offset;
        while (pos < offset + length) {
                unsigned int end_of_block, range_to_discard;

                err = 0;

                /* The length of space left to zero and unmap */
                range_to_discard = offset + length - pos;

                /* The length of space until the end of the block */
                end_of_block = blocksize - (pos & (blocksize-1));

                /*
                 * Do not unmap or zero past end of block
                 * for this buffer head
                 */
                if (range_to_discard > end_of_block)
                        range_to_discard = end_of_block;


                /*
                 * Skip this buffer head if we are only zeroing unampped
                 * regions of the page
                 */
                if (flags & EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED &&
                        buffer_mapped(bh))
                                goto next;

                /* If the range is block aligned, unmap */
                if (range_to_discard == blocksize) {
                        clear_buffer_dirty(bh);
                        bh->b_bdev = NULL;
                        clear_buffer_mapped(bh);
                        clear_buffer_req(bh);
                        clear_buffer_new(bh);
                        clear_buffer_delay(bh);
                        clear_buffer_unwritten(bh);
                        clear_buffer_uptodate(bh);
                        zero_user(page, pos, range_to_discard);
                        BUFFER_TRACE(bh, "Buffer discarded");
                        goto next;
                }

                /*
                 * If this block is not completely contained in the range
                 * to be discarded, then it is not going to be released. Because
                 * we need to keep this block, we need to make sure this part
                 * of the page is uptodate before we modify it by writeing
                 * partial zeros on it.
                 */
                if (!buffer_mapped(bh)) {
                        /*
                         * Buffer head must be mapped before we can read
                         * from the block
                         */
                        BUFFER_TRACE(bh, "unmapped");
                        ext4_get_block(inode, iblock, bh, 0);
                        /* unmapped? It's a hole - nothing to do */
                        if (!buffer_mapped(bh)) {
                                BUFFER_TRACE(bh, "still unmapped");
                                goto next;
                        }
                }

                /* Ok, it's mapped. Make sure it's up-to-date */
                if (PageUptodate(page))
                        set_buffer_uptodate(bh);

                if (!buffer_uptodate(bh)) {
                        err = -EIO;
                        ll_rw_block(READ, 1, &bh);
                        wait_on_buffer(bh);
                        /* Uhhuh. Read error. Complain and punt.*/
                        if (!buffer_uptodate(bh))
                                goto next;
                }

                if (ext4_should_journal_data(inode)) {
                        BUFFER_TRACE(bh, "get write access");
                        err = ext4_journal_get_write_access(handle, bh);
                        if (err)
                                goto next;
                }

                zero_user(page, pos, range_to_discard);

                err = 0;
                if (ext4_should_journal_data(inode)) {
                        err = ext4_handle_dirty_metadata(handle, inode, bh);
                } else
                        mark_buffer_dirty(bh);

                BUFFER_TRACE(bh, "Partial buffer zeroed");
next:
                bh = bh->b_this_page;
                iblock++;
                pos += range_to_discard;
        }

        return err;
}

int ext4_can_truncate(struct inode *inode)
{
        if (S_ISREG(inode->i_mode))
                return 1;
        if (S_ISDIR(inode->i_mode))
                return 1;
        if (S_ISLNK(inode->i_mode))
                return !ext4_inode_is_fast_symlink(inode);
        return 0;
}

/*
 * ext4_punch_hole: punches a hole in a file by releaseing the blocks
 * associated with the given offset and length
 *
 * @inode:  File inode
 * @offset: The offset where the hole will begin
 * @len:    The length of the hole
 *
 * Returns: 0 on success or negative on failure
 */

int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
{
        struct inode *inode = file->f_path.dentry->d_inode;
        if (!S_ISREG(inode->i_mode))
                return -EOPNOTSUPP;

        if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                return ext4_ind_punch_hole(file, offset, length);

        if (EXT4_SB(inode->i_sb)->s_cluster_ratio > 1) {
                /* TODO: Add support for bigalloc file systems */
                return -EOPNOTSUPP;
        }

        trace_ext4_punch_hole(inode, offset, length);

        return ext4_ext_punch_hole(file, offset, length);
}

/*
 * ext4_truncate()
 *
 * We block out ext4_get_block() block instantiations across the entire
 * transaction, and VFS/VM ensures that ext4_truncate() cannot run
 * simultaneously on behalf of the same inode.
 *
 * As we work through the truncate and commit bits of it to the journal there
 * is one core, guiding principle: the file's tree must always be consistent on
 * disk.  We must be able to restart the truncate after a crash.
 *
 * The file's tree may be transiently inconsistent in memory (although it
 * probably isn't), but whenever we close off and commit a journal transaction,
 * the contents of (the filesystem + the journal) must be consistent and
 * restartable.  It's pretty simple, really: bottom up, right to left (although
 * left-to-right works OK too).
 *
 * Note that at recovery time, journal replay occurs *before* the restart of
 * truncate against the orphan inode list.
 *
 * The committed inode has the new, desired i_size (which is the same as
 * i_disksize in this case).  After a crash, ext4_orphan_cleanup() will see
 * that this inode's truncate did not complete and it will again call
 * ext4_truncate() to have another go.  So there will be instantiated blocks
 * to the right of the truncation point in a crashed ext4 filesystem.  But
 * that's fine - as long as they are linked from the inode, the post-crash
 * ext4_truncate() run will find them and release them.
 */
void ext4_truncate(struct inode *inode)
{
        trace_ext4_truncate_enter(inode);

        if (!ext4_can_truncate(inode))
                return;

        ext4_clear_inode_flag(inode, EXT4_INODE_EOFBLOCKS);

        if (inode->i_size == 0 && !test_opt(inode->i_sb, NO_AUTO_DA_ALLOC))
                ext4_set_inode_state(inode, EXT4_STATE_DA_ALLOC_CLOSE);

        if (ext4_has_inline_data(inode)) {
                int has_inline = 1;

                ext4_inline_data_truncate(inode, &has_inline);
                if (has_inline)
                        return;
        }

        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                ext4_ext_truncate(inode);
        else
                ext4_ind_truncate(inode);

        trace_ext4_truncate_exit(inode);
}

/*
 * ext4_get_inode_loc returns with an extra refcount against the inode's
 * underlying buffer_head on success. If 'in_mem' is true, we have all
 * data in memory that is needed to recreate the on-disk version of this
 * inode.
 */
static int __ext4_get_inode_loc(struct inode *inode,
                                struct ext4_iloc *iloc, int in_mem)
{
        struct ext4_group_desc  *gdp;
        struct buffer_head      *bh;
        struct super_block      *sb = inode->i_sb;
        ext4_fsblk_t            block;
        int                     inodes_per_block, inode_offset;

        iloc->bh = NULL;
        if (!ext4_valid_inum(sb, inode->i_ino))
                return -EIO;

        iloc->block_group = (inode->i_ino - 1) / EXT4_INODES_PER_GROUP(sb);
        gdp = ext4_get_group_desc(sb, iloc->block_group, NULL);
        if (!gdp)
                return -EIO;

        /*
         * Figure out the offset within the block group inode table
         */
        inodes_per_block = EXT4_SB(sb)->s_inodes_per_block;
        inode_offset = ((inode->i_ino - 1) %
                        EXT4_INODES_PER_GROUP(sb));
        block = ext4_inode_table(sb, gdp) + (inode_offset / inodes_per_block);
        iloc->offset = (inode_offset % inodes_per_block) * EXT4_INODE_SIZE(sb);

        bh = sb_getblk(sb, block);
        if (unlikely(!bh))
                return -ENOMEM;
        if (!buffer_uptodate(bh)) {
                lock_buffer(bh);

                /*
                 * If the buffer has the write error flag, we have failed
                 * to write out another inode in the same block.  In this
                 * case, we don't have to read the block because we may
                 * read the old inode data successfully.
                 */
                if (buffer_write_io_error(bh) && !buffer_uptodate(bh))
                        set_buffer_uptodate(bh);

                if (buffer_uptodate(bh)) {
                        /* someone brought it uptodate while we waited */
                        unlock_buffer(bh);
                        goto has_buffer;
                }

                /*
                 * If we have all information of the inode in memory and this
                 * is the only valid inode in the block, we need not read the
                 * block.
                 */
                if (in_mem) {
                        struct buffer_head *bitmap_bh;
                        int i, start;

                        start = inode_offset & ~(inodes_per_block - 1);

                        /* Is the inode bitmap in cache? */
                        bitmap_bh = sb_getblk(sb, ext4_inode_bitmap(sb, gdp));
                        if (unlikely(!bitmap_bh))
                                goto make_io;

                        /*
                         * If the inode bitmap isn't in cache then the
                         * optimisation may end up performing two reads instead
                         * of one, so skip it.
                         */
                        if (!buffer_uptodate(bitmap_bh)) {
                                brelse(bitmap_bh);
                                goto make_io;
                        }
                        for (i = start; i < start + inodes_per_block; i++) {
                                if (i == inode_offset)
                                        continue;
                                if (ext4_test_bit(i, bitmap_bh->b_data))
                                        break;
                        }
                        brelse(bitmap_bh);
                        if (i == start + inodes_per_block) {
                                /* all other inodes are free, so skip I/O */
                                memset(bh->b_data, 0, bh->b_size);
                                set_buffer_uptodate(bh);
                                unlock_buffer(bh);
                                goto has_buffer;
                        }
                }

make_io:
                /*
                 * If we need to do any I/O, try to pre-readahead extra
                 * blocks from the inode table.
                 */
                if (EXT4_SB(sb)->s_inode_readahead_blks) {
                        ext4_fsblk_t b, end, table;
                        unsigned num;

                        table = ext4_inode_table(sb, gdp);
                        /* s_inode_readahead_blks is always a power of 2 */
                        b = block & ~(EXT4_SB(sb)->s_inode_readahead_blks-1);
                        if (table > b)
                                b = table;
                        end = b + EXT4_SB(sb)->s_inode_readahead_blks;
                        num = EXT4_INODES_PER_GROUP(sb);
                        if (ext4_has_group_desc_csum(sb))
                                num -= ext4_itable_unused_count(sb, gdp);
                        table += num / inodes_per_block;
                        if (end > table)
                                end = table;
                        while (b <= end)
                                sb_breadahead(sb, b++);
                }

                /*
                 * There are other valid inodes in the buffer, this inode
                 * has in-inode xattrs, or we don't have this inode in memory.
                 * Read the block from disk.
                 */
                trace_ext4_load_inode(inode);
                get_bh(bh);
                bh->b_end_io = end_buffer_read_sync;
                submit_bh(READ | REQ_META | REQ_PRIO, bh);
                wait_on_buffer(bh);
                if (!buffer_uptodate(bh)) {
                        EXT4_ERROR_INODE_BLOCK(inode, block,
                                               "unable to read itable block");
                        brelse(bh);
                        return -EIO;
                }
        }
has_buffer:
        iloc->bh = bh;
        return 0;
}

int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc)
{
        /* We have all inode data except xattrs in memory here. */
        return __ext4_get_inode_loc(inode, iloc,
                !ext4_test_inode_state(inode, EXT4_STATE_XATTR));
}

void ext4_set_inode_flags(struct inode *inode)
{
        unsigned int flags = EXT4_I(inode)->i_flags;

        inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
        if (flags & EXT4_SYNC_FL)
                inode->i_flags |= S_SYNC;
        if (flags & EXT4_APPEND_FL)
                inode->i_flags |= S_APPEND;
        if (flags & EXT4_IMMUTABLE_FL)
                inode->i_flags |= S_IMMUTABLE;
        if (flags & EXT4_NOATIME_FL)
                inode->i_flags |= S_NOATIME;
        if (flags & EXT4_DIRSYNC_FL)
                inode->i_flags |= S_DIRSYNC;
}

/* Propagate flags from i_flags to EXT4_I(inode)->i_flags */
void ext4_get_inode_flags(struct ext4_inode_info *ei)
{
        unsigned int vfs_fl;
        unsigned long old_fl, new_fl;

        do {
                vfs_fl = ei->vfs_inode.i_flags;
                old_fl = ei->i_flags;
                new_fl = old_fl & ~(EXT4_SYNC_FL|EXT4_APPEND_FL|
                                EXT4_IMMUTABLE_FL|EXT4_NOATIME_FL|
                                EXT4_DIRSYNC_FL);
                if (vfs_fl & S_SYNC)
                        new_fl |= EXT4_SYNC_FL;
                if (vfs_fl & S_APPEND)
                        new_fl |= EXT4_APPEND_FL;
                if (vfs_fl & S_IMMUTABLE)
                        new_fl |= EXT4_IMMUTABLE_FL;
                if (vfs_fl & S_NOATIME)
                        new_fl |= EXT4_NOATIME_FL;
                if (vfs_fl & S_DIRSYNC)
                        new_fl |= EXT4_DIRSYNC_FL;
        } while (cmpxchg(&ei->i_flags, old_fl, new_fl) != old_fl);
}

static blkcnt_t ext4_inode_blocks(struct ext4_inode *raw_inode,
                                  struct ext4_inode_info *ei)
{
        blkcnt_t i_blocks ;
        struct inode *inode = &(ei->vfs_inode);
        struct super_block *sb = inode->i_sb;

        if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
                                EXT4_FEATURE_RO_COMPAT_HUGE_FILE)) {
                /* we are using combined 48 bit field */
                i_blocks = ((u64)le16_to_cpu(raw_inode->i_blocks_high)) << 32 |
                                        le32_to_cpu(raw_inode->i_blocks_lo);
                if (ext4_test_inode_flag(inode, EXT4_INODE_HUGE_FILE)) {
                        /* i_blocks represent file system block size */
                        return i_blocks  << (inode->i_blkbits - 9);
                } else {
                        return i_blocks;
                }
        } else {
                return le32_to_cpu(raw_inode->i_blocks_lo);
        }
}

static inline void ext4_iget_extra_inode(struct inode *inode,
                                         struct ext4_inode *raw_inode,
                                         struct ext4_inode_info *ei)
{
        __le32 *magic = (void *)raw_inode +
                        EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize;
        if (*magic == cpu_to_le32(EXT4_XATTR_MAGIC)) {
                ext4_set_inode_state(inode, EXT4_STATE_XATTR);
                ext4_find_inline_data_nolock(inode);
        } else
                EXT4_I(inode)->i_inline_off = 0;
}

struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
{
        struct ext4_iloc iloc;
        struct ext4_inode *raw_inode;
        struct ext4_inode_info *ei;
        struct inode *inode;
        journal_t *journal = EXT4_SB(sb)->s_journal;
        long ret;
        int block;
        uid_t i_uid;
        gid_t i_gid;

        inode = iget_locked(sb, ino);
        if (!inode)
                return ERR_PTR(-ENOMEM);
        if (!(inode->i_state & I_NEW))
                return inode;

        ei = EXT4_I(inode);
        iloc.bh = NULL;

        ret = __ext4_get_inode_loc(inode, &iloc, 0);
        if (ret < 0)
                goto bad_inode;
        raw_inode = ext4_raw_inode(&iloc);

        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
                ei->i_extra_isize = le16_to_cpu(raw_inode->i_extra_isize);
                if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize >
                    EXT4_INODE_SIZE(inode->i_sb)) {
                        EXT4_ERROR_INODE(inode, "bad extra_isize (%u != %u)",
                                EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize,
                                EXT4_INODE_SIZE(inode->i_sb));
                        ret = -EIO;
                        goto bad_inode;
                }
        } else
                ei->i_extra_isize = 0;

        /* Precompute checksum seed for inode metadata */
        if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
                        EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) {
                struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
                __u32 csum;
                __le32 inum = cpu_to_le32(inode->i_ino);
                __le32 gen = raw_inode->i_generation;
                csum = ext4_chksum(sbi, sbi->s_csum_seed, (__u8 *)&inum,
                                   sizeof(inum));
                ei->i_csum_seed = ext4_chksum(sbi, csum, (__u8 *)&gen,
                                              sizeof(gen));
        }

        if (!ext4_inode_csum_verify(inode, raw_inode, ei)) {
                EXT4_ERROR_INODE(inode, "checksum invalid");
                ret = -EIO;
                goto bad_inode;
        }

        inode->i_mode = le16_to_cpu(raw_inode->i_mode);
        i_uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low);
        i_gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);
        if (!(test_opt(inode->i_sb, NO_UID32))) {
                i_uid |= le16_to_cpu(raw_inode->i_uid_high) << 16;
                i_gid |= le16_to_cpu(raw_inode->i_gid_high) << 16;
        }
        i_uid_write(inode, i_uid);
        i_gid_write(inode, i_gid);
        set_nlink(inode, le16_to_cpu(raw_inode->i_links_count));

        ext4_clear_state_flags(ei);     /* Only relevant on 32-bit archs */
        ei->i_inline_off = 0;
        ei->i_dir_start_lookup = 0;
        ei->i_dtime = le32_to_cpu(raw_inode->i_dtime);
        /* We now have enough fields to check if the inode was active or not.
         * This is needed because nfsd might try to access dead inodes
         * the test is that same one that e2fsck uses
         * NeilBrown 1999oct15
         */
        if (inode->i_nlink == 0) {
                if (inode->i_mode == 0 ||
                    !(EXT4_SB(inode->i_sb)->s_mount_state & EXT4_ORPHAN_FS)) {
                        /* this inode is deleted */
                        ret = -ESTALE;
                        goto bad_inode;
                }
                /* The only unlinked inodes we let through here have
                 * valid i_mode and are being read by the orphan
                 * recovery code: that's fine, we're about to complete
                 * the process of deleting those. */
        }
        ei->i_flags = le32_to_cpu(raw_inode->i_flags);
        inode->i_blocks = ext4_inode_blocks(raw_inode, ei);
        ei->i_file_acl = le32_to_cpu(raw_inode->i_file_acl_lo);
        if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_64BIT))
                ei->i_file_acl |=
                        ((__u64)le16_to_cpu(raw_inode->i_file_acl_high)) << 32;
        inode->i_size = ext4_isize(raw_inode);
        ei->i_disksize = inode->i_size;
#ifdef CONFIG_QUOTA
        ei->i_reserved_quota = 0;
#endif
        inode->i_generation = le32_to_cpu(raw_inode->i_generation);
        ei->i_block_group = iloc.block_group;
        ei->i_last_alloc_group = ~0;
        /*
         * NOTE! The in-memory inode i_data array is in little-endian order
         * even on big-endian machines: we do NOT byteswap the block numbers!
         */
        for (block = 0; block < EXT4_N_BLOCKS; block++)
                ei->i_data[block] = raw_inode->i_block[block];
        INIT_LIST_HEAD(&ei->i_orphan);

        /*
         * Set transaction id's of transactions that have to be committed
         * to finish f[data]sync. We set them to currently running transaction
         * as we cannot be sure that the inode or some of its metadata isn't
         * part of the transaction - the inode could have been reclaimed and
         * now it is reread from disk.
         */
        if (journal) {
                transaction_t *transaction;
                tid_t tid;

                read_lock(&journal->j_state_lock);
                if (journal->j_running_transaction)
                        transaction = journal->j_running_transaction;
                else
                        transaction = journal->j_committing_transaction;
                if (transaction)
                        tid = transaction->t_tid;
                else
                        tid = journal->j_commit_sequence;
                read_unlock(&journal->j_state_lock);
                ei->i_sync_tid = tid;
                ei->i_datasync_tid = tid;
        }

        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
                if (ei->i_extra_isize == 0) {
                        /* The extra space is currently unused. Use it. */
                        ei->i_extra_isize = sizeof(struct ext4_inode) -
                                            EXT4_GOOD_OLD_INODE_SIZE;
                } else {
                        ext4_iget_extra_inode(inode, raw_inode, ei);
                }
        }

        EXT4_INODE_GET_XTIME(i_ctime, inode, raw_inode);
        EXT4_INODE_GET_XTIME(i_mtime, inode, raw_inode);
        EXT4_INODE_GET_XTIME(i_atime, inode, raw_inode);
        EXT4_EINODE_GET_XTIME(i_crtime, ei, raw_inode);

        inode->i_version = le32_to_cpu(raw_inode->i_disk_version);
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
                if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
                        inode->i_version |=
                        (__u64)(le32_to_cpu(raw_inode->i_version_hi)) << 32;
        }

        ret = 0;
        if (ei->i_file_acl &&
            !ext4_data_block_valid(EXT4_SB(sb), ei->i_file_acl, 1)) {
                EXT4_ERROR_INODE(inode, "bad extended attribute block %llu",
                                 ei->i_file_acl);
                ret = -EIO;
                goto bad_inode;
        } else if (!ext4_has_inline_data(inode)) {
                if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
                        if ((S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
                            (S_ISLNK(inode->i_mode) &&
                             !ext4_inode_is_fast_symlink(inode))))
                                /* Validate extent which is part of inode */
                                ret = ext4_ext_check_inode(inode);
                } else if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
                           (S_ISLNK(inode->i_mode) &&
                            !ext4_inode_is_fast_symlink(inode))) {
                        /* Validate block references which are part of inode */
                        ret = ext4_ind_check_inode(inode);
                }
        }
        if (ret)
                goto bad_inode;

        if (S_ISREG(inode->i_mode)) {
                inode->i_op = &ext4_file_inode_operations;
                inode->i_fop = &ext4_file_operations;
                ext4_set_aops(inode);
        } else if (S_ISDIR(inode->i_mode)) {
                inode->i_op = &ext4_dir_inode_operations;
                inode->i_fop = &ext4_dir_operations;
        } else if (S_ISLNK(inode->i_mode)) {
                if (ext4_inode_is_fast_symlink(inode)) {
                        inode->i_op = &ext4_fast_symlink_inode_operations;
                        nd_terminate_link(ei->i_data, inode->i_size,
                                sizeof(ei->i_data) - 1);
                } else {
                        inode->i_op = &ext4_symlink_inode_operations;
                        ext4_set_aops(inode);
                }
        } else if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode) ||
              S_ISFIFO(inode->i_mode) || S_ISSOCK(inode->i_mode)) {
                inode->i_op = &ext4_special_inode_operations;
                if (raw_inode->i_block[0])
                        init_special_inode(inode, inode->i_mode,
                           old_decode_dev(le32_to_cpu(raw_inode->i_block[0])));
                else
                        init_special_inode(inode, inode->i_mode,
                           new_decode_dev(le32_to_cpu(raw_inode->i_block[1])));
        } else {
                ret = -EIO;
                EXT4_ERROR_INODE(inode, "bogus i_mode (%o)", inode->i_mode);
                goto bad_inode;
        }
        brelse(iloc.bh);
        ext4_set_inode_flags(inode);
        unlock_new_inode(inode);
        return inode;

bad_inode:
        brelse(iloc.bh);
        iget_failed(inode);
        return ERR_PTR(ret);
}

static int ext4_inode_blocks_set(handle_t *handle,
                                struct ext4_inode *raw_inode,
                                struct ext4_inode_info *ei)
{
        struct inode *inode = &(ei->vfs_inode);
        u64 i_blocks = inode->i_blocks;
        struct super_block *sb = inode->i_sb;

        if (i_blocks <= ~0U) {
                /*
                 * i_blocks can be represented in a 32 bit variable
                 * as multiple of 512 bytes
                 */
                raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
                raw_inode->i_blocks_high = 0;
                ext4_clear_inode_flag(inode, EXT4_INODE_HUGE_FILE);
                return 0;
        }
        if (!EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_HUGE_FILE))
                return -EFBIG;

        if (i_blocks <= 0xffffffffffffULL) {
                /*
                 * i_blocks can be represented in a 48 bit variable
                 * as multiple of 512 bytes
                 */
                raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
                raw_inode->i_blocks_high = cpu_to_le16(i_blocks >> 32);
                ext4_clear_inode_flag(inode, EXT4_INODE_HUGE_FILE);
        } else {
                ext4_set_inode_flag(inode, EXT4_INODE_HUGE_FILE);
                /* i_block is stored in file system block size */
                i_blocks = i_blocks >> (inode->i_blkbits - 9);
                raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
                raw_inode->i_blocks_high = cpu_to_le16(i_blocks >> 32);
        }
        return 0;
}

/*
 * Post the struct inode info into an on-disk inode location in the
 * buffer-cache.  This gobbles the caller's reference to the
 * buffer_head in the inode location struct.
 *
 * The caller must have write access to iloc->bh.
 */
static int ext4_do_update_inode(handle_t *handle,
                                struct inode *inode,
                                struct ext4_iloc *iloc)
{
        struct ext4_inode *raw_inode = ext4_raw_inode(iloc);
        struct ext4_inode_info *ei = EXT4_I(inode);
        struct buffer_head *bh = iloc->bh;
        int err = 0, rc, block;
        int need_datasync = 0;
        uid_t i_uid;
        gid_t i_gid;

        /* For fields not not tracking in the in-memory inode,
         * initialise them to zero for new inodes. */
        if (ext4_test_inode_state(inode, EXT4_STATE_NEW))
                memset(raw_inode, 0, EXT4_SB(inode->i_sb)->s_inode_size);

        ext4_get_inode_flags(ei);
        raw_inode->i_mode = cpu_to_le16(inode->i_mode);
        i_uid = i_uid_read(inode);
        i_gid = i_gid_read(inode);
        if (!(test_opt(inode->i_sb, NO_UID32))) {
                raw_inode->i_uid_low = cpu_to_le16(low_16_bits(i_uid));
                raw_inode->i_gid_low = cpu_to_le16(low_16_bits(i_gid));
/*
 * Fix up interoperability with old kernels. Otherwise, old inodes get
 * re-used with the upper 16 bits of the uid/gid intact
 */
                if (!ei->i_dtime) {
                        raw_inode->i_uid_high =
                                cpu_to_le16(high_16_bits(i_uid));
                        raw_inode->i_gid_high =
                                cpu_to_le16(high_16_bits(i_gid));
                } else {
                        raw_inode->i_uid_high = 0;
                        raw_inode->i_gid_high = 0;
                }
        } else {
                raw_inode->i_uid_low = cpu_to_le16(fs_high2lowuid(i_uid));
                raw_inode->i_gid_low = cpu_to_le16(fs_high2lowgid(i_gid));
                raw_inode->i_uid_high = 0;
                raw_inode->i_gid_high = 0;
        }
        raw_inode->i_links_count = cpu_to_le16(inode->i_nlink);

        EXT4_INODE_SET_XTIME(i_ctime, inode, raw_inode);
        EXT4_INODE_SET_XTIME(i_mtime, inode, raw_inode);
        EXT4_INODE_SET_XTIME(i_atime, inode, raw_inode);
        EXT4_EINODE_SET_XTIME(i_crtime, ei, raw_inode);

        if (ext4_inode_blocks_set(handle, raw_inode, ei))
                goto out_brelse;
        raw_inode->i_dtime = cpu_to_le32(ei->i_dtime);
        raw_inode->i_flags = cpu_to_le32(ei->i_flags & 0xFFFFFFFF);
        if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
            cpu_to_le32(EXT4_OS_HURD))
                raw_inode->i_file_acl_high =
                        cpu_to_le16(ei->i_file_acl >> 32);
        raw_inode->i_file_acl_lo = cpu_to_le32(ei->i_file_acl);
        if (ei->i_disksize != ext4_isize(raw_inode)) {
                ext4_isize_set(raw_inode, ei->i_disksize);
                need_datasync = 1;
        }
        if (ei->i_disksize > 0x7fffffffULL) {
                struct super_block *sb = inode->i_sb;
                if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
                                EXT4_FEATURE_RO_COMPAT_LARGE_FILE) ||
                                EXT4_SB(sb)->s_es->s_rev_level ==
                                cpu_to_le32(EXT4_GOOD_OLD_REV)) {
                        /* If this is the first large file
                         * created, add a flag to the superblock.
                         */
                        err = ext4_journal_get_write_access(handle,
                                        EXT4_SB(sb)->s_sbh);
                        if (err)
                                goto out_brelse;
                        ext4_update_dynamic_rev(sb);
                        EXT4_SET_RO_COMPAT_FEATURE(sb,
                                        EXT4_FEATURE_RO_COMPAT_LARGE_FILE);
                        ext4_handle_sync(handle);
                        err = ext4_handle_dirty_super(handle, sb);
                }
        }
        raw_inode->i_generation = cpu_to_le32(inode->i_generation);
        if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode)) {
                if (old_valid_dev(inode->i_rdev)) {
                        raw_inode->i_block[0] =
                                cpu_to_le32(old_encode_dev(inode->i_rdev));
                        raw_inode->i_block[1] = 0;
                } else {
                        raw_inode->i_block[0] = 0;
                        raw_inode->i_block[1] =
                                cpu_to_le32(new_encode_dev(inode->i_rdev));
                        raw_inode->i_block[2] = 0;
                }
        } else if (!ext4_has_inline_data(inode)) {
                for (block = 0; block < EXT4_N_BLOCKS; block++)
                        raw_inode->i_block[block] = ei->i_data[block];
        }

        raw_inode->i_disk_version = cpu_to_le32(inode->i_version);
        if (ei->i_extra_isize) {
                if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
                        raw_inode->i_version_hi =
                        cpu_to_le32(inode->i_version >> 32);
                raw_inode->i_extra_isize = cpu_to_le16(ei->i_extra_isize);
        }

        ext4_inode_csum_set(inode, raw_inode, ei);

        BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
        rc = ext4_handle_dirty_metadata(handle, NULL, bh);
        if (!err)
                err = rc;
        ext4_clear_inode_state(inode, EXT4_STATE_NEW);

        ext4_update_inode_fsync_trans(handle, inode, need_datasync);
out_brelse:
        brelse(bh);
        ext4_std_error(inode->i_sb, err);
        return err;
}

/*
 * ext4_write_inode()
 *
 * We are called from a few places:
 *
 * - Within generic_file_write() for O_SYNC files.
 *   Here, there will be no transaction running. We wait for any running
 *   transaction to commit.
 *
 * - Within sys_sync(), kupdate and such.
 *   We wait on commit, if tol to.
 *
 * - Within prune_icache() (PF_MEMALLOC == true)
 *   Here we simply return.  We can't afford to block kswapd on the
 *   journal commit.
 *
 * In all cases it is actually safe for us to return without doing anything,
 * because the inode has been copied into a raw inode buffer in
 * ext4_mark_inode_dirty().  This is a correctness thing for O_SYNC and for
 * knfsd.
 *
 * Note that we are absolutely dependent upon all inode dirtiers doing the
 * right thing: they *must* call mark_inode_dirty() after dirtying info in
 * which we are interested.
 *
 * It would be a bug for them to not do this.  The code:
 *
 *      mark_inode_dirty(inode)
 *      stuff();
 *      inode->i_size = expr;
 *
 * is in error because a kswapd-driven write_inode() could occur while
 * `stuff()' is running, and the new i_size will be lost.  Plus the inode
 * will no longer be on the superblock's dirty inode list.
 */
int ext4_write_inode(struct inode *inode, struct writeback_control *wbc)
{
        int err;

        if (current->flags & PF_MEMALLOC)
                return 0;

        if (EXT4_SB(inode->i_sb)->s_journal) {
                if (ext4_journal_current_handle()) {
                        jbd_debug(1, "called recursively, non-PF_MEMALLOC!\n");
                        dump_stack();
                        return -EIO;
                }

                if (wbc->sync_mode != WB_SYNC_ALL)
                        return 0;

                err = ext4_force_commit(inode->i_sb);
        } else {
                struct ext4_iloc iloc;

                err = __ext4_get_inode_loc(inode, &iloc, 0);
                if (err)
                        return err;
                if (wbc->sync_mode == WB_SYNC_ALL)
                        sync_dirty_buffer(iloc.bh);
                if (buffer_req(iloc.bh) && !buffer_uptodate(iloc.bh)) {
                        EXT4_ERROR_INODE_BLOCK(inode, iloc.bh->b_blocknr,
                                         "IO error syncing inode");
                        err = -EIO;
                }
                brelse(iloc.bh);
        }
        return err;
}

/*
 * In data=journal mode ext4_journalled_invalidatepage() may fail to invalidate
 * buffers that are attached to a page stradding i_size and are undergoing
 * commit. In that case we have to wait for commit to finish and try again.
 */
static void ext4_wait_for_tail_page_commit(struct inode *inode)
{
        struct page *page;
        unsigned offset;
        journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
        tid_t commit_tid = 0;
        int ret;

        offset = inode->i_size & (PAGE_CACHE_SIZE - 1);
        /*
         * All buffers in the last page remain valid? Then there's nothing to
         * do. We do the check mainly to optimize the common PAGE_CACHE_SIZE ==
         * blocksize case
         */
        if (offset > PAGE_CACHE_SIZE - (1 << inode->i_blkbits))
                return;
        while (1) {
                page = find_lock_page(inode->i_mapping,
                                      inode->i_size >> PAGE_CACHE_SHIFT);
                if (!page)
                        return;
                ret = __ext4_journalled_invalidatepage(page, offset);
                unlock_page(page);
                page_cache_release(page);
                if (ret != -EBUSY)
                        return;
                commit_tid = 0;
                read_lock(&journal->j_state_lock);
                if (journal->j_committing_transaction)
                        commit_tid = journal->j_committing_transaction->t_tid;
                read_unlock(&journal->j_state_lock);
                if (commit_tid)
                        jbd2_log_wait_commit(journal, commit_tid);
        }
}

/*
 * ext4_setattr()
 *
 * Called from notify_change.
 *
 * We want to trap VFS attempts to truncate the file as soon as
 * possible.  In particular, we want to make sure that when the VFS
 * shrinks i_size, we put the inode on the orphan list and modify
 * i_disksize immediately, so that during the subsequent flushing of
 * dirty pages and freeing of disk blocks, we can guarantee that any
 * commit will leave the blocks being flushed in an unused state on
 * disk.  (On recovery, the inode will get truncated and the blocks will
 * be freed, so we have a strong guarantee that no future commit will
 * leave these blocks visible to the user.)
 *
 * Another thing we have to assure is that if we are in ordered mode
 * and inode is still attached to the committing transaction, we must
 * we start writeout of all the dirty pages which are being truncated.
 * This way we are sure that all the data written in the previous
 * transaction are already on disk (truncate waits for pages under
 * writeback).
 *
 * Called with inode->i_mutex down.
 */
int ext4_setattr(struct dentry *dentry, struct iattr *attr)
{
        struct inode *inode = dentry->d_inode;
        int error, rc = 0;
        int orphan = 0;
        const unsigned int ia_valid = attr->ia_valid;

        error = inode_change_ok(inode, attr);
        if (error)
                return error;

        if (is_quota_modification(inode, attr))
                dquot_initialize(inode);
        if ((ia_valid & ATTR_UID && !uid_eq(attr->ia_uid, inode->i_uid)) ||
            (ia_valid & ATTR_GID && !gid_eq(attr->ia_gid, inode->i_gid))) {
                handle_t *handle;

                /* (user+group)*(old+new) structure, inode write (sb,
                 * inode block, ? - but truncate inode update has it) */
                handle = ext4_journal_start(inode, (EXT4_MAXQUOTAS_INIT_BLOCKS(inode->i_sb)+
                                        EXT4_MAXQUOTAS_DEL_BLOCKS(inode->i_sb))+3);
                if (IS_ERR(handle)) {
                        error = PTR_ERR(handle);
                        goto err_out;
                }
                error = dquot_transfer(inode, attr);
                if (error) {
                        ext4_journal_stop(handle);
                        return error;
                }
                /* Update corresponding info in inode so that everything is in
                 * one transaction */
                if (attr->ia_valid & ATTR_UID)
                        inode->i_uid = attr->ia_uid;
                if (attr->ia_valid & ATTR_GID)
                        inode->i_gid = attr->ia_gid;
                error = ext4_mark_inode_dirty(handle, inode);
                ext4_journal_stop(handle);
        }

        if (attr->ia_valid & ATTR_SIZE) {

                if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
                        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);

                        if (attr->ia_size > sbi->s_bitmap_maxbytes)
                                return -EFBIG;
                }
        }

        if (S_ISREG(inode->i_mode) &&
            attr->ia_valid & ATTR_SIZE &&
            (attr->ia_size < inode->i_size)) {
                handle_t *handle;

                handle = ext4_journal_start(inode, 3);
                if (IS_ERR(handle)) {
                        error = PTR_ERR(handle);
                        goto err_out;
                }
                if (ext4_handle_valid(handle)) {
                        error = ext4_orphan_add(handle, inode);
                        orphan = 1;
                }
                EXT4_I(inode)->i_disksize = attr->ia_size;
                rc = ext4_mark_inode_dirty(handle, inode);
                if (!error)
                        error = rc;
                ext4_journal_stop(handle);

                if (ext4_should_order_data(inode)) {
                        error = ext4_begin_ordered_truncate(inode,
                                                            attr->ia_size);
                        if (error) {
                                /* Do as much error cleanup as possible */
                                handle = ext4_journal_start(inode, 3);
                                if (IS_ERR(handle)) {
                                        ext4_orphan_del(NULL, inode);
                                        goto err_out;
                                }
                                ext4_orphan_del(handle, inode);
                                orphan = 0;
                                ext4_journal_stop(handle);
                                goto err_out;
                        }
                }
        }

        if (attr->ia_valid & ATTR_SIZE) {
                if (attr->ia_size != inode->i_size) {
                        loff_t oldsize = inode->i_size;

                        i_size_write(inode, attr->ia_size);
                        /*
                         * Blocks are going to be removed from the inode. Wait
                         * for dio in flight.  Temporarily disable
                         * dioread_nolock to prevent livelock.
                         */
                        if (orphan) {
                                if (!ext4_should_journal_data(inode)) {
                                        ext4_inode_block_unlocked_dio(inode);
                                        inode_dio_wait(inode);
                                        ext4_inode_resume_unlocked_dio(inode);
                                } else
                                        ext4_wait_for_tail_page_commit(inode);
                        }
                        /*
                         * Truncate pagecache after we've waited for commit
                         * in data=journal mode to make pages freeable.
                         */
                        truncate_pagecache(inode, oldsize, inode->i_size);
                }
                ext4_truncate(inode);
        }

        if (!rc) {
                setattr_copy(inode, attr);
                mark_inode_dirty(inode);
        }

        /*
         * If the call to ext4_truncate failed to get a transaction handle at
         * all, we need to clean up the in-core orphan list manually.
         */
        if (orphan && inode->i_nlink)
                ext4_orphan_del(NULL, inode);

        if (!rc && (ia_valid & ATTR_MODE))
                rc = ext4_acl_chmod(inode);

err_out:
        ext4_std_error(inode->i_sb, error);
        if (!error)
                error = rc;
        return error;
}

int ext4_getattr(struct vfsmount *mnt, struct dentry *dentry,
                 struct kstat *stat)
{
        struct inode *inode;
        unsigned long delalloc_blocks;

        inode = dentry->d_inode;
        generic_fillattr(inode, stat);

        /*
         * We can't update i_blocks if the block allocation is delayed
         * otherwise in the case of system crash before the real block
         * allocation is done, we will have i_blocks inconsistent with
         * on-disk file blocks.
         * We always keep i_blocks updated together with real
         * allocation. But to not confuse with user, stat
         * will return the blocks that include the delayed allocation
         * blocks for this file.
         */
        delalloc_blocks = EXT4_C2B(EXT4_SB(inode->i_sb),
                                EXT4_I(inode)->i_reserved_data_blocks);

        stat->blocks += (delalloc_blocks << inode->i_sb->s_blocksize_bits)>>9;
        return 0;
}

static int ext4_index_trans_blocks(struct inode *inode, int nrblocks, int chunk)
{
        if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
                return ext4_ind_trans_blocks(inode, nrblocks, chunk);
        return ext4_ext_index_trans_blocks(inode, nrblocks, chunk);
}

/*
 * Account for index blocks, block groups bitmaps and block group
 * descriptor blocks if modify datablocks and index blocks
 * worse case, the indexs blocks spread over different block groups
 *
 * If datablocks are discontiguous, they are possible to spread over
 * different block groups too. If they are contiguous, with flexbg,
 * they could still across block group boundary.
 *
 * Also account for superblock, inode, quota and xattr blocks
 */
static int ext4_meta_trans_blocks(struct inode *inode, int nrblocks, int chunk)
{
        ext4_group_t groups, ngroups = ext4_get_groups_count(inode->i_sb);
        int gdpblocks;
        int idxblocks;
        int ret = 0;

        /*
         * How many index blocks need to touch to modify nrblocks?
         * The "Chunk" flag indicating whether the nrblocks is
         * physically contiguous on disk
         *
         * For Direct IO and fallocate, they calls get_block to allocate
         * one single extent at a time, so they could set the "Chunk" flag
         */
        idxblocks = ext4_index_trans_blocks(inode, nrblocks, chunk);

        ret = idxblocks;

        /*
         * Now let's see how many group bitmaps and group descriptors need
         * to account
         */
        groups = idxblocks;
        if (chunk)
                groups += 1;
        else
                groups += nrblocks;

        gdpblocks = groups;
        if (groups > ngroups)
                groups = ngroups;
        if (groups > EXT4_SB(inode->i_sb)->s_gdb_count)
                gdpblocks = EXT4_SB(inode->i_sb)->s_gdb_count;

        /* bitmaps and block group descriptor blocks */
        ret += groups + gdpblocks;

        /* Blocks for super block, inode, quota and xattr blocks */
        ret += EXT4_META_TRANS_BLOCKS(inode->i_sb);

        return ret;
}

/*
 * Calculate the total number of credits to reserve to fit
 * the modification of a single pages into a single transaction,
 * which may include multiple chunks of block allocations.
 *
 * This could be called via ext4_write_begin()
 *
 * We need to consider the worse case, when
 * one new block per extent.
 */
int ext4_writepage_trans_blocks(struct inode *inode)
{
        int bpp = ext4_journal_blocks_per_page(inode);
        int ret;

        ret = ext4_meta_trans_blocks(inode, bpp, 0);

        /* Account for data blocks for journalled mode */
        if (ext4_should_journal_data(inode))
                ret += bpp;
        return ret;
}

/*
 * Calculate the journal credits for a chunk of data modification.
 *
 * This is called from DIO, fallocate or whoever calling
 * ext4_map_blocks() to map/allocate a chunk of contiguous disk blocks.
 *
 * journal buffers for data blocks are not included here, as DIO
 * and fallocate do no need to journal data buffers.
 */
int ext4_chunk_trans_blocks(struct inode *inode, int nrblocks)
{
        return ext4_meta_trans_blocks(inode, nrblocks, 1);
}

/*
 * The caller must have previously called ext4_reserve_inode_write().
 * Give this, we know that the caller already has write access to iloc->bh.
 */
int ext4_mark_iloc_dirty(handle_t *handle,
                         struct inode *inode, struct ext4_iloc *iloc)
{
        int err = 0;

        if (IS_I_VERSION(inode))
                inode_inc_iversion(inode);

        /* the do_update_inode consumes one bh->b_count */
        get_bh(iloc->bh);

        /* ext4_do_update_inode() does jbd2_journal_dirty_metadata */
        err = ext4_do_update_inode(handle, inode, iloc);
        put_bh(iloc->bh);
        return err;
}

/*
 * On success, We end up with an outstanding reference count against
 * iloc->bh.  This _must_ be cleaned up later.
 */

int
ext4_reserve_inode_write(handle_t *handle, struct inode *inode,
                         struct ext4_iloc *iloc)
{
        int err;

        err = ext4_get_inode_loc(inode, iloc);
        if (!err) {
                BUFFER_TRACE(iloc->bh, "get_write_access");
                err = ext4_journal_get_write_access(handle, iloc->bh);
                if (err) {
                        brelse(iloc->bh);
                        iloc->bh = NULL;
                }
        }
        ext4_std_error(inode->i_sb, err);
        return err;
}

/*
 * Expand an inode by new_extra_isize bytes.
 * Returns 0 on success or negative error number on failure.
 */
static int ext4_expand_extra_isize(struct inode *inode,
                                   unsigned int new_extra_isize,
                                   struct ext4_iloc iloc,
                                   handle_t *handle)
{
        struct ext4_inode *raw_inode;
        struct ext4_xattr_ibody_header *header;

        if (EXT4_I(inode)->i_extra_isize >= new_extra_isize)
                return 0;

        raw_inode = ext4_raw_inode(&iloc);

        header = IHDR(inode, raw_inode);

        /* No extended attributes present */
        if (!ext4_test_inode_state(inode, EXT4_STATE_XATTR) ||
            header->h_magic != cpu_to_le32(EXT4_XATTR_MAGIC)) {
                memset((void *)raw_inode + EXT4_GOOD_OLD_INODE_SIZE, 0,
                        new_extra_isize);
                EXT4_I(inode)->i_extra_isize = new_extra_isize;
                return 0;
        }

        /* try to expand with EAs present */
        return ext4_expand_extra_isize_ea(inode, new_extra_isize,
                                          raw_inode, handle);
}

/*
 * What we do here is to mark the in-core inode as clean with respect to inode
 * dirtiness (it may still be data-dirty).
 * This means that the in-core inode may be reaped by prune_icache
 * without having to perform any I/O.  This is a very good thing,
 * because *any* task may call prune_icache - even ones which
 * have a transaction open against a different journal.
 *
 * Is this cheating?  Not really.  Sure, we haven't written the
 * inode out, but prune_icache isn't a user-visible syncing function.
 * Whenever the user wants stuff synced (sys_sync, sys_msync, sys_fsync)
 * we start and wait on commits.
 */
int ext4_mark_inode_dirty(handle_t *handle, struct inode *inode)
{
        struct ext4_iloc iloc;
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        static unsigned int mnt_count;
        int err, ret;

        might_sleep();
        trace_ext4_mark_inode_dirty(inode, _RET_IP_);
        err = ext4_reserve_inode_write(handle, inode, &iloc);
        if (ext4_handle_valid(handle) &&
            EXT4_I(inode)->i_extra_isize < sbi->s_want_extra_isize &&
            !ext4_test_inode_state(inode, EXT4_STATE_NO_EXPAND)) {
                /*
                 * We need extra buffer credits since we may write into EA block
                 * with this same handle. If journal_extend fails, then it will
                 * only result in a minor loss of functionality for that inode.
                 * If this is felt to be critical, then e2fsck should be run to
                 * force a large enough s_min_extra_isize.
                 */
                if ((jbd2_journal_extend(handle,
                             EXT4_DATA_TRANS_BLOCKS(inode->i_sb))) == 0) {
                        ret = ext4_expand_extra_isize(inode,
                                                      sbi->s_want_extra_isize,
                                                      iloc, handle);
                        if (ret) {
                                ext4_set_inode_state(inode,
                                                     EXT4_STATE_NO_EXPAND);
                                if (mnt_count !=
                                        le16_to_cpu(sbi->s_es->s_mnt_count)) {
                                        ext4_warning(inode->i_sb,
                                        "Unable to expand inode %lu. Delete"
                                        " some EAs or run e2fsck.",
                                        inode->i_ino);
                                        mnt_count =
                                          le16_to_cpu(sbi->s_es->s_mnt_count);
                                }
                        }
                }
        }
        if (!err)
                err = ext4_mark_iloc_dirty(handle, inode, &iloc);
        return err;
}

/*
 * ext4_dirty_inode() is called from __mark_inode_dirty()
 *
 * We're really interested in the case where a file is being extended.
 * i_size has been changed by generic_commit_write() and we thus need
 * to include the updated inode in the current transaction.
 *
 * Also, dquot_alloc_block() will always dirty the inode when blocks
 * are allocated to the file.
 *
 * If the inode is marked synchronous, we don't honour that here - doing
 * so would cause a commit on atime updates, which we don't bother doing.
 * We handle synchronous inodes at the highest possible level.
 */
void ext4_dirty_inode(struct inode *inode, int flags)
{
        handle_t *handle;

        handle = ext4_journal_start(inode, 2);
        if (IS_ERR(handle))
                goto out;

        ext4_mark_inode_dirty(handle, inode);

        ext4_journal_stop(handle);
out:
        return;
}

#if 0
/*
 * Bind an inode's backing buffer_head into this transaction, to prevent
 * it from being flushed to disk early.  Unlike
 * ext4_reserve_inode_write, this leaves behind no bh reference and
 * returns no iloc structure, so the caller needs to repeat the iloc
 * lookup to mark the inode dirty later.
 */
static int ext4_pin_inode(handle_t *handle, struct inode *inode)
{
        struct ext4_iloc iloc;

        int err = 0;
        if (handle) {
                err = ext4_get_inode_loc(inode, &iloc);
                if (!err) {
                        BUFFER_TRACE(iloc.bh, "get_write_access");
                        err = jbd2_journal_get_write_access(handle, iloc.bh);
                        if (!err)
                                err = ext4_handle_dirty_metadata(handle,
                                                                 NULL,
                                                                 iloc.bh);
                        brelse(iloc.bh);
                }
        }
        ext4_std_error(inode->i_sb, err);
        return err;
}
#endif

int ext4_change_inode_journal_flag(struct inode *inode, int val)
{
        journal_t *journal;
        handle_t *handle;
        int err;

        /*
         * We have to be very careful here: changing a data block's
         * journaling status dynamically is dangerous.  If we write a
         * data block to the journal, change the status and then delete
         * that block, we risk forgetting to revoke the old log record
         * from the journal and so a subsequent replay can corrupt data.
         * So, first we make sure that the journal is empty and that
         * nobody is changing anything.
         */

        journal = EXT4_JOURNAL(inode);
        if (!journal)
                return 0;
        if (is_journal_aborted(journal))
                return -EROFS;
        /* We have to allocate physical blocks for delalloc blocks
         * before flushing journal. otherwise delalloc blocks can not
         * be allocated any more. even more truncate on delalloc blocks
         * could trigger BUG by flushing delalloc blocks in journal.
         * There is no delalloc block in non-journal data mode.
         */
        if (val && test_opt(inode->i_sb, DELALLOC)) {
                err = ext4_alloc_da_blocks(inode);
                if (err < 0)
                        return err;
        }

        /* Wait for all existing dio workers */
        ext4_inode_block_unlocked_dio(inode);
        inode_dio_wait(inode);

        jbd2_journal_lock_updates(journal);

        /*
         * OK, there are no updates running now, and all cached data is
         * synced to disk.  We are now in a completely consistent state
         * which doesn't have anything in the journal, and we know that
         * no filesystem updates are running, so it is safe to modify
         * the inode's in-core data-journaling state flag now.
         */

        if (val)
                ext4_set_inode_flag(inode, EXT4_INODE_JOURNAL_DATA);
        else {
                jbd2_journal_flush(journal);
                ext4_clear_inode_flag(inode, EXT4_INODE_JOURNAL_DATA);
        }
        ext4_set_aops(inode);

        jbd2_journal_unlock_updates(journal);
        ext4_inode_resume_unlocked_dio(inode);

        /* Finally we can mark the inode as dirty. */

        handle = ext4_journal_start(inode, 1);
        if (IS_ERR(handle))
                return PTR_ERR(handle);

        err = ext4_mark_inode_dirty(handle, inode);
        ext4_handle_sync(handle);
        ext4_journal_stop(handle);
        ext4_std_error(inode->i_sb, err);

        return err;
}

static int ext4_bh_unmapped(handle_t *handle, struct buffer_head *bh)
{
        return !buffer_mapped(bh);
}

int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
{
        struct page *page = vmf->page;
        loff_t size;
        unsigned long len;
        int ret;
        struct file *file = vma->vm_file;
        struct inode *inode = file->f_path.dentry->d_inode;
        struct address_space *mapping = inode->i_mapping;
        handle_t *handle;
        get_block_t *get_block;
        int retries = 0;

        sb_start_pagefault(inode->i_sb);
        file_update_time(vma->vm_file);
        /* Delalloc case is easy... */
        if (test_opt(inode->i_sb, DELALLOC) &&
            !ext4_should_journal_data(inode) &&
            !ext4_nonda_switch(inode->i_sb)) {
                do {
                        ret = __block_page_mkwrite(vma, vmf,
                                                   ext4_da_get_block_prep);
                } while (ret == -ENOSPC &&
                       ext4_should_retry_alloc(inode->i_sb, &retries));
                goto out_ret;
        }

        lock_page(page);
        size = i_size_read(inode);
        /* Page got truncated from under us? */
        if (page->mapping != mapping || page_offset(page) > size) {
                unlock_page(page);
                ret = VM_FAULT_NOPAGE;
                goto out;
        }

        if (page->index == size >> PAGE_CACHE_SHIFT)
                len = size & ~PAGE_CACHE_MASK;
        else
                len = PAGE_CACHE_SIZE;
        /*
         * Return if we have all the buffers mapped. This avoids the need to do
         * journal_start/journal_stop which can block and take a long time
         */
        if (page_has_buffers(page)) {
                if (!ext4_walk_page_buffers(NULL, page_buffers(page),
                                            0, len, NULL,
                                            ext4_bh_unmapped)) {
                        /* Wait so that we don't change page under IO */
                        wait_on_page_writeback(page);
                        ret = VM_FAULT_LOCKED;
                        goto out;
                }
        }
        unlock_page(page);
        /* OK, we need to fill the hole... */
        if (ext4_should_dioread_nolock(inode))
                get_block = ext4_get_block_write;
        else
                get_block = ext4_get_block;
retry_alloc:
        handle = ext4_journal_start(inode, ext4_writepage_trans_blocks(inode));
        if (IS_ERR(handle)) {
                ret = VM_FAULT_SIGBUS;
                goto out;
        }
        ret = __block_page_mkwrite(vma, vmf, get_block);
        if (!ret && ext4_should_journal_data(inode)) {
                if (ext4_walk_page_buffers(handle, page_buffers(page), 0,
                          PAGE_CACHE_SIZE, NULL, do_journal_get_write_access)) {
                        unlock_page(page);
                        ret = VM_FAULT_SIGBUS;
                        ext4_journal_stop(handle);
                        goto out;
                }
                ext4_set_inode_state(inode, EXT4_STATE_JDATA);
        }
        ext4_journal_stop(handle);
        if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
                goto retry_alloc;
out_ret:
        ret = block_page_mkwrite_return(ret);
out:
        sb_end_pagefault(inode->i_sb);
        return ret;
}