ext4: Add new ext4 inode tracepoints

[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
 *
 *  Goal-directed block allocation by Stephen Tweedie
 *      (sct@redhat.com), 1993, 1998
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller (davem@caip.rutgers.edu), 1995
 *  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/module.h>
#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/slab.h>

#include "ext4_jbd2.h"
#include "xattr.h"
#include "acl.h"
#include "ext4_extents.h"

#include <trace/events/ext4.h>

#define MPAGE_DA_EXTENT_TAIL 0x01

static inline int ext4_begin_ordered_truncate(struct inode *inode,
                                              loff_t new_size)
{
        trace_ext4_begin_ordered_truncate(inode, new_size);
        return jbd2_journal_begin_ordered_truncate(
                                        EXT4_SB(inode->i_sb)->s_journal,
                                        &EXT4_I(inode)->jinode,
                                        new_size);
}

static void ext4_invalidatepage(struct page *page, unsigned long offset);
static int noalloc_get_block_write(struct inode *inode, sector_t iblock,
                                   struct buffer_head *bh_result, int create);
static int ext4_set_bh_endio(struct buffer_head *bh, struct inode *inode);
static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate);
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);

/*
 * 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);
}

/*
 * Work out how many blocks we need to proceed with the next chunk of a
 * truncate transaction.
 */
static unsigned long blocks_for_truncate(struct inode *inode)
{
        ext4_lblk_t needed;

        needed = inode->i_blocks >> (inode->i_sb->s_blocksize_bits - 9);

        /* Give ourselves just enough room to cope with inodes in which
         * i_blocks is corrupt: we've seen disk corruptions in the past
         * which resulted in random data in an inode which looked enough
         * like a regular file for ext4 to try to delete it.  Things
         * will go a bit crazy if that happens, but at least we should
         * try not to panic the whole kernel. */
        if (needed < 2)
                needed = 2;

        /* But we need to bound the transaction so we don't overflow the
         * journal. */
        if (needed > EXT4_MAX_TRANS_DATA)
                needed = EXT4_MAX_TRANS_DATA;

        return EXT4_DATA_TRANS_BLOCKS(inode->i_sb) + needed;
}

/*
 * Truncate transactions can be complex and absolutely huge.  So we need to
 * be able to restart the transaction at a conventient checkpoint to make
 * sure we don't overflow the journal.
 *
 * start_transaction gets us a new handle for a truncate transaction,
 * and extend_transaction tries to extend the existing one a bit.  If
 * extend fails, we need to propagate the failure up and restart the
 * transaction in the top-level truncate loop. --sct
 */
static handle_t *start_transaction(struct inode *inode)
{
        handle_t *result;

        result = ext4_journal_start(inode, blocks_for_truncate(inode));
        if (!IS_ERR(result))
                return result;

        ext4_std_error(inode->i_sb, PTR_ERR(result));
        return result;
}

/*
 * Try to extend this transaction for the purposes of truncation.
 *
 * Returns 0 if we managed to create more room.  If we can't create more
 * room, and the transaction must be restarted we return 1.
 */
static int try_to_extend_transaction(handle_t *handle, struct inode *inode)
{
        if (!ext4_handle_valid(handle))
                return 0;
        if (ext4_handle_has_enough_credits(handle, EXT4_RESERVE_TRANS_BLOCKS+1))
                return 0;
        if (!ext4_journal_extend(handle, blocks_for_truncate(inode)))
                return 0;
        return 1;
}

/*
 * 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, blocks_for_truncate(inode));
        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);
        if (inode->i_nlink) {
                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;

        handle = ext4_journal_start(inode, 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);
                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);
                        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);
        return;
no_delete:
        ext4_clear_inode(inode);        /* We must guarantee clearing of inode... */
}

typedef struct {
        __le32  *p;
        __le32  key;
        struct buffer_head *bh;
} Indirect;

static inline void add_chain(Indirect *p, struct buffer_head *bh, __le32 *v)
{
        p->key = *(p->p = v);
        p->bh = bh;
}

/**
 *      ext4_block_to_path - parse the block number into array of offsets
 *      @inode: inode in question (we are only interested in its superblock)
 *      @i_block: block number to be parsed
 *      @offsets: array to store the offsets in
 *      @boundary: set this non-zero if the referred-to block is likely to be
 *             followed (on disk) by an indirect block.
 *
 *      To store the locations of file's data ext4 uses a data structure common
 *      for UNIX filesystems - tree of pointers anchored in the inode, with
 *      data blocks at leaves and indirect blocks in intermediate nodes.
 *      This function translates the block number into path in that tree -
 *      return value is the path length and @offsets[n] is the offset of
 *      pointer to (n+1)th node in the nth one. If @block is out of range
 *      (negative or too large) warning is printed and zero returned.
 *
 *      Note: function doesn't find node addresses, so no IO is needed. All
 *      we need to know is the capacity of indirect blocks (taken from the
 *      inode->i_sb).
 */

/*
 * Portability note: the last comparison (check that we fit into triple
 * indirect block) is spelled differently, because otherwise on an
 * architecture with 32-bit longs and 8Kb pages we might get into trouble
 * if our filesystem had 8Kb blocks. We might use long long, but that would
 * kill us on x86. Oh, well, at least the sign propagation does not matter -
 * i_block would have to be negative in the very beginning, so we would not
 * get there at all.
 */

static int ext4_block_to_path(struct inode *inode,
                              ext4_lblk_t i_block,
                              ext4_lblk_t offsets[4], int *boundary)
{
        int ptrs = EXT4_ADDR_PER_BLOCK(inode->i_sb);
        int ptrs_bits = EXT4_ADDR_PER_BLOCK_BITS(inode->i_sb);
        const long direct_blocks = EXT4_NDIR_BLOCKS,
                indirect_blocks = ptrs,
                double_blocks = (1 << (ptrs_bits * 2));
        int n = 0;
        int final = 0;

        if (i_block < direct_blocks) {
                offsets[n++] = i_block;
                final = direct_blocks;
        } else if ((i_block -= direct_blocks) < indirect_blocks) {
                offsets[n++] = EXT4_IND_BLOCK;
                offsets[n++] = i_block;
                final = ptrs;
        } else if ((i_block -= indirect_blocks) < double_blocks) {
                offsets[n++] = EXT4_DIND_BLOCK;
                offsets[n++] = i_block >> ptrs_bits;
                offsets[n++] = i_block & (ptrs - 1);
                final = ptrs;
        } else if (((i_block -= double_blocks) >> (ptrs_bits * 2)) < ptrs) {
                offsets[n++] = EXT4_TIND_BLOCK;
                offsets[n++] = i_block >> (ptrs_bits * 2);
                offsets[n++] = (i_block >> ptrs_bits) & (ptrs - 1);
                offsets[n++] = i_block & (ptrs - 1);
                final = ptrs;
        } else {
                ext4_warning(inode->i_sb, "block %lu > max in inode %lu",
                             i_block + direct_blocks +
                             indirect_blocks + double_blocks, inode->i_ino);
        }
        if (boundary)
                *boundary = final - 1 - (i_block & (ptrs - 1));
        return n;
}

static int __ext4_check_blockref(const char *function, unsigned int line,
                                 struct inode *inode,
                                 __le32 *p, unsigned int max)
{
        struct ext4_super_block *es = EXT4_SB(inode->i_sb)->s_es;
        __le32 *bref = p;
        unsigned int blk;

        while (bref < p+max) {
                blk = le32_to_cpu(*bref++);
                if (blk &&
                    unlikely(!ext4_data_block_valid(EXT4_SB(inode->i_sb),
                                                    blk, 1))) {
                        es->s_last_error_block = cpu_to_le64(blk);
                        ext4_error_inode(inode, function, line, blk,
                                         "invalid block");
                        return -EIO;
                }
        }
        return 0;
}


#define ext4_check_indirect_blockref(inode, bh)                         \
        __ext4_check_blockref(__func__, __LINE__, inode,                \
                              (__le32 *)(bh)->b_data,                   \
                              EXT4_ADDR_PER_BLOCK((inode)->i_sb))

#define ext4_check_inode_blockref(inode)                                \
        __ext4_check_blockref(__func__, __LINE__, inode,                \
                              EXT4_I(inode)->i_data,                    \
                              EXT4_NDIR_BLOCKS)

/**
 *      ext4_get_branch - read the chain of indirect blocks leading to data
 *      @inode: inode in question
 *      @depth: depth of the chain (1 - direct pointer, etc.)
 *      @offsets: offsets of pointers in inode/indirect blocks
 *      @chain: place to store the result
 *      @err: here we store the error value
 *
 *      Function fills the array of triples <key, p, bh> and returns %NULL
 *      if everything went OK or the pointer to the last filled triple
 *      (incomplete one) otherwise. Upon the return chain[i].key contains
 *      the number of (i+1)-th block in the chain (as it is stored in memory,
 *      i.e. little-endian 32-bit), chain[i].p contains the address of that
 *      number (it points into struct inode for i==0 and into the bh->b_data
 *      for i>0) and chain[i].bh points to the buffer_head of i-th indirect
 *      block for i>0 and NULL for i==0. In other words, it holds the block
 *      numbers of the chain, addresses they were taken from (and where we can
 *      verify that chain did not change) and buffer_heads hosting these
 *      numbers.
 *
 *      Function stops when it stumbles upon zero pointer (absent block)
 *              (pointer to last triple returned, *@err == 0)
 *      or when it gets an IO error reading an indirect block
 *              (ditto, *@err == -EIO)
 *      or when it reads all @depth-1 indirect blocks successfully and finds
 *      the whole chain, all way to the data (returns %NULL, *err == 0).
 *
 *      Need to be called with
 *      down_read(&EXT4_I(inode)->i_data_sem)
 */
static Indirect *ext4_get_branch(struct inode *inode, int depth,
                                 ext4_lblk_t  *offsets,
                                 Indirect chain[4], int *err)
{
        struct super_block *sb = inode->i_sb;
        Indirect *p = chain;
        struct buffer_head *bh;

        *err = 0;
        /* i_data is not going away, no lock needed */
        add_chain(chain, NULL, EXT4_I(inode)->i_data + *offsets);
        if (!p->key)
                goto no_block;
        while (--depth) {
                bh = sb_getblk(sb, le32_to_cpu(p->key));
                if (unlikely(!bh))
                        goto failure;

                if (!bh_uptodate_or_lock(bh)) {
                        if (bh_submit_read(bh) < 0) {
                                put_bh(bh);
                                goto failure;
                        }
                        /* validate block references */
                        if (ext4_check_indirect_blockref(inode, bh)) {
                                put_bh(bh);
                                goto failure;
                        }
                }

                add_chain(++p, bh, (__le32 *)bh->b_data + *++offsets);
                /* Reader: end */
                if (!p->key)
                        goto no_block;
        }
        return NULL;

failure:
        *err = -EIO;
no_block:
        return p;
}

/**
 *      ext4_find_near - find a place for allocation with sufficient locality
 *      @inode: owner
 *      @ind: descriptor of indirect block.
 *
 *      This function returns the preferred place for block allocation.
 *      It is used when heuristic for sequential allocation fails.
 *      Rules are:
 *        + if there is a block to the left of our position - allocate near it.
 *        + if pointer will live in indirect block - allocate near that block.
 *        + if pointer will live in inode - allocate in the same
 *          cylinder group.
 *
 * In the latter case we colour the starting block by the callers PID to
 * prevent it from clashing with concurrent allocations for a different inode
 * in the same block group.   The PID is used here so that functionally related
 * files will be close-by on-disk.
 *
 *      Caller must make sure that @ind is valid and will stay that way.
 */
static ext4_fsblk_t ext4_find_near(struct inode *inode, Indirect *ind)
{
        struct ext4_inode_info *ei = EXT4_I(inode);
        __le32 *start = ind->bh ? (__le32 *) ind->bh->b_data : ei->i_data;
        __le32 *p;
        ext4_fsblk_t bg_start;
        ext4_fsblk_t last_block;
        ext4_grpblk_t colour;
        ext4_group_t block_group;
        int flex_size = ext4_flex_bg_size(EXT4_SB(inode->i_sb));

        /* Try to find previous block */
        for (p = ind->p - 1; p >= start; p--) {
                if (*p)
                        return le32_to_cpu(*p);
        }

        /* No such thing, so let's try location of indirect block */
        if (ind->bh)
                return ind->bh->b_blocknr;

        /*
         * It is going to be referred to from the inode itself? OK, just put it
         * into the same cylinder group then.
         */
        block_group = ei->i_block_group;
        if (flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) {
                block_group &= ~(flex_size-1);
                if (S_ISREG(inode->i_mode))
                        block_group++;
        }
        bg_start = ext4_group_first_block_no(inode->i_sb, block_group);
        last_block = ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es) - 1;

        /*
         * If we are doing delayed allocation, we don't need take
         * colour into account.
         */
        if (test_opt(inode->i_sb, DELALLOC))
                return bg_start;

        if (bg_start + EXT4_BLOCKS_PER_GROUP(inode->i_sb) <= last_block)
                colour = (current->pid % 16) *
                        (EXT4_BLOCKS_PER_GROUP(inode->i_sb) / 16);
        else
                colour = (current->pid % 16) * ((last_block - bg_start) / 16);
        return bg_start + colour;
}

/**
 *      ext4_find_goal - find a preferred place for allocation.
 *      @inode: owner
 *      @block:  block we want
 *      @partial: pointer to the last triple within a chain
 *
 *      Normally this function find the preferred place for block allocation,
 *      returns it.
 *      Because this is only used for non-extent files, we limit the block nr
 *      to 32 bits.
 */
static ext4_fsblk_t ext4_find_goal(struct inode *inode, ext4_lblk_t block,
                                   Indirect *partial)
{
        ext4_fsblk_t goal;

        /*
         * XXX need to get goal block from mballoc's data structures
         */

        goal = ext4_find_near(inode, partial);
        goal = goal & EXT4_MAX_BLOCK_FILE_PHYS;
        return goal;
}

/**
 *      ext4_blks_to_allocate: Look up the block map and count the number
 *      of direct blocks need to be allocated for the given branch.
 *
 *      @branch: chain of indirect blocks
 *      @k: number of blocks need for indirect blocks
 *      @blks: number of data blocks to be mapped.
 *      @blocks_to_boundary:  the offset in the indirect block
 *
 *      return the total number of blocks to be allocate, including the
 *      direct and indirect blocks.
 */
static int ext4_blks_to_allocate(Indirect *branch, int k, unsigned int blks,
                                 int blocks_to_boundary)
{
        unsigned int count = 0;

        /*
         * Simple case, [t,d]Indirect block(s) has not allocated yet
         * then it's clear blocks on that path have not allocated
         */
        if (k > 0) {
                /* right now we don't handle cross boundary allocation */
                if (blks < blocks_to_boundary + 1)
                        count += blks;
                else
                        count += blocks_to_boundary + 1;
                return count;
        }

        count++;
        while (count < blks && count <= blocks_to_boundary &&
                le32_to_cpu(*(branch[0].p + count)) == 0) {
                count++;
        }
        return count;
}

/**
 *      ext4_alloc_blocks: multiple allocate blocks needed for a branch
 *      @indirect_blks: the number of blocks need to allocate for indirect
 *                      blocks
 *
 *      @new_blocks: on return it will store the new block numbers for
 *      the indirect blocks(if needed) and the first direct block,
 *      @blks:  on return it will store the total number of allocated
 *              direct blocks
 */
static int ext4_alloc_blocks(handle_t *handle, struct inode *inode,
                             ext4_lblk_t iblock, ext4_fsblk_t goal,
                             int indirect_blks, int blks,
                             ext4_fsblk_t new_blocks[4], int *err)
{
        struct ext4_allocation_request ar;
        int target, i;
        unsigned long count = 0, blk_allocated = 0;
        int index = 0;
        ext4_fsblk_t current_block = 0;
        int ret = 0;

        /*
         * Here we try to allocate the requested multiple blocks at once,
         * on a best-effort basis.
         * To build a branch, we should allocate blocks for
         * the indirect blocks(if not allocated yet), and at least
         * the first direct block of this branch.  That's the
         * minimum number of blocks need to allocate(required)
         */
        /* first we try to allocate the indirect blocks */
        target = indirect_blks;
        while (target > 0) {
                count = target;
                /* allocating blocks for indirect blocks and direct blocks */
                current_block = ext4_new_meta_blocks(handle, inode,
                                                        goal, &count, err);
                if (*err)
                        goto failed_out;

                if (unlikely(current_block + count > EXT4_MAX_BLOCK_FILE_PHYS)) {
                        EXT4_ERROR_INODE(inode,
                                         "current_block %llu + count %lu > %d!",
                                         current_block, count,
                                         EXT4_MAX_BLOCK_FILE_PHYS);
                        *err = -EIO;
                        goto failed_out;
                }

                target -= count;
                /* allocate blocks for indirect blocks */
                while (index < indirect_blks && count) {
                        new_blocks[index++] = current_block++;
                        count--;
                }
                if (count > 0) {
                        /*
                         * save the new block number
                         * for the first direct block
                         */
                        new_blocks[index] = current_block;
                        printk(KERN_INFO "%s returned more blocks than "
                                                "requested\n", __func__);
                        WARN_ON(1);
                        break;
                }
        }

        target = blks - count ;
        blk_allocated = count;
        if (!target)
                goto allocated;
        /* Now allocate data blocks */
        memset(&ar, 0, sizeof(ar));
        ar.inode = inode;
        ar.goal = goal;
        ar.len = target;
        ar.logical = iblock;
        if (S_ISREG(inode->i_mode))
                /* enable in-core preallocation only for regular files */
                ar.flags = EXT4_MB_HINT_DATA;

        current_block = ext4_mb_new_blocks(handle, &ar, err);
        if (unlikely(current_block + ar.len > EXT4_MAX_BLOCK_FILE_PHYS)) {
                EXT4_ERROR_INODE(inode,
                                 "current_block %llu + ar.len %d > %d!",
                                 current_block, ar.len,
                                 EXT4_MAX_BLOCK_FILE_PHYS);
                *err = -EIO;
                goto failed_out;
        }

        if (*err && (target == blks)) {
                /*
                 * if the allocation failed and we didn't allocate
                 * any blocks before
                 */
                goto failed_out;
        }
        if (!*err) {
                if (target == blks) {
                        /*
                         * save the new block number
                         * for the first direct block
                         */
                        new_blocks[index] = current_block;
                }
                blk_allocated += ar.len;
        }
allocated:
        /* total number of blocks allocated for direct blocks */
        ret = blk_allocated;
        *err = 0;
        return ret;
failed_out:
        for (i = 0; i < index; i++)
                ext4_free_blocks(handle, inode, 0, new_blocks[i], 1, 0);
        return ret;
}

/**
 *      ext4_alloc_branch - allocate and set up a chain of blocks.
 *      @inode: owner
 *      @indirect_blks: number of allocated indirect blocks
 *      @blks: number of allocated direct blocks
 *      @offsets: offsets (in the blocks) to store the pointers to next.
 *      @branch: place to store the chain in.
 *
 *      This function allocates blocks, zeroes out all but the last one,
 *      links them into chain and (if we are synchronous) writes them to disk.
 *      In other words, it prepares a branch that can be spliced onto the
 *      inode. It stores the information about that chain in the branch[], in
 *      the same format as ext4_get_branch() would do. We are calling it after
 *      we had read the existing part of chain and partial points to the last
 *      triple of that (one with zero ->key). Upon the exit we have the same
 *      picture as after the successful ext4_get_block(), except that in one
 *      place chain is disconnected - *branch->p is still zero (we did not
 *      set the last link), but branch->key contains the number that should
 *      be placed into *branch->p to fill that gap.
 *
 *      If allocation fails we free all blocks we've allocated (and forget
 *      their buffer_heads) and return the error value the from failed
 *      ext4_alloc_block() (normally -ENOSPC). Otherwise we set the chain
 *      as described above and return 0.
 */
static int ext4_alloc_branch(handle_t *handle, struct inode *inode,
                             ext4_lblk_t iblock, int indirect_blks,
                             int *blks, ext4_fsblk_t goal,
                             ext4_lblk_t *offsets, Indirect *branch)
{
        int blocksize = inode->i_sb->s_blocksize;
        int i, n = 0;
        int err = 0;
        struct buffer_head *bh;
        int num;
        ext4_fsblk_t new_blocks[4];
        ext4_fsblk_t current_block;

        num = ext4_alloc_blocks(handle, inode, iblock, goal, indirect_blks,
                                *blks, new_blocks, &err);
        if (err)
                return err;

        branch[0].key = cpu_to_le32(new_blocks[0]);
        /*
         * metadata blocks and data blocks are allocated.
         */
        for (n = 1; n <= indirect_blks;  n++) {
                /*
                 * Get buffer_head for parent block, zero it out
                 * and set the pointer to new one, then send
                 * parent to disk.
                 */
                bh = sb_getblk(inode->i_sb, new_blocks[n-1]);
                if (unlikely(!bh)) {
                        err = -EIO;
                        goto failed;
                }

                branch[n].bh = bh;
                lock_buffer(bh);
                BUFFER_TRACE(bh, "call get_create_access");
                err = ext4_journal_get_create_access(handle, bh);
                if (err) {
                        /* Don't brelse(bh) here; it's done in
                         * ext4_journal_forget() below */
                        unlock_buffer(bh);
                        goto failed;
                }

                memset(bh->b_data, 0, blocksize);
                branch[n].p = (__le32 *) bh->b_data + offsets[n];
                branch[n].key = cpu_to_le32(new_blocks[n]);
                *branch[n].p = branch[n].key;
                if (n == indirect_blks) {
                        current_block = new_blocks[n];
                        /*
                         * End of chain, update the last new metablock of
                         * the chain to point to the new allocated
                         * data blocks numbers
                         */
                        for (i = 1; i < num; i++)
                                *(branch[n].p + i) = cpu_to_le32(++current_block);
                }
                BUFFER_TRACE(bh, "marking uptodate");
                set_buffer_uptodate(bh);
                unlock_buffer(bh);

                BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
                err = ext4_handle_dirty_metadata(handle, inode, bh);
                if (err)
                        goto failed;
        }
        *blks = num;
        return err;
failed:
        /* Allocation failed, free what we already allocated */
        ext4_free_blocks(handle, inode, 0, new_blocks[0], 1, 0);
        for (i = 1; i <= n ; i++) {
                /*
                 * branch[i].bh is newly allocated, so there is no
                 * need to revoke the block, which is why we don't
                 * need to set EXT4_FREE_BLOCKS_METADATA.
                 */
                ext4_free_blocks(handle, inode, 0, new_blocks[i], 1,
                                 EXT4_FREE_BLOCKS_FORGET);
        }
        for (i = n+1; i < indirect_blks; i++)
                ext4_free_blocks(handle, inode, 0, new_blocks[i], 1, 0);

        ext4_free_blocks(handle, inode, 0, new_blocks[i], num, 0);

        return err;
}

/**
 * ext4_splice_branch - splice the allocated branch onto inode.
 * @inode: owner
 * @block: (logical) number of block we are adding
 * @chain: chain of indirect blocks (with a missing link - see
 *      ext4_alloc_branch)
 * @where: location of missing link
 * @num:   number of indirect blocks we are adding
 * @blks:  number of direct blocks we are adding
 *
 * This function fills the missing link and does all housekeeping needed in
 * inode (->i_blocks, etc.). In case of success we end up with the full
 * chain to new block and return 0.
 */
static int ext4_splice_branch(handle_t *handle, struct inode *inode,
                              ext4_lblk_t block, Indirect *where, int num,
                              int blks)
{
        int i;
        int err = 0;
        ext4_fsblk_t current_block;

        /*
         * If we're splicing into a [td]indirect block (as opposed to the
         * inode) then we need to get write access to the [td]indirect block
         * before the splice.
         */
        if (where->bh) {
                BUFFER_TRACE(where->bh, "get_write_access");
                err = ext4_journal_get_write_access(handle, where->bh);
                if (err)
                        goto err_out;
        }
        /* That's it */

        *where->p = where->key;

        /*
         * Update the host buffer_head or inode to point to more just allocated
         * direct blocks blocks
         */
        if (num == 0 && blks > 1) {
                current_block = le32_to_cpu(where->key) + 1;
                for (i = 1; i < blks; i++)
                        *(where->p + i) = cpu_to_le32(current_block++);
        }

        /* We are done with atomic stuff, now do the rest of housekeeping */
        /* had we spliced it onto indirect block? */
        if (where->bh) {
                /*
                 * If we spliced it onto an indirect block, we haven't
                 * altered the inode.  Note however that if it is being spliced
                 * onto an indirect block at the very end of the file (the
                 * file is growing) then we *will* alter the inode to reflect
                 * the new i_size.  But that is not done here - it is done in
                 * generic_commit_write->__mark_inode_dirty->ext4_dirty_inode.
                 */
                jbd_debug(5, "splicing indirect only\n");
                BUFFER_TRACE(where->bh, "call ext4_handle_dirty_metadata");
                err = ext4_handle_dirty_metadata(handle, inode, where->bh);
                if (err)
                        goto err_out;
        } else {
                /*
                 * OK, we spliced it into the inode itself on a direct block.
                 */
                ext4_mark_inode_dirty(handle, inode);
                jbd_debug(5, "splicing direct\n");
        }
        return err;

err_out:
        for (i = 1; i <= num; i++) {
                /*
                 * branch[i].bh is newly allocated, so there is no
                 * need to revoke the block, which is why we don't
                 * need to set EXT4_FREE_BLOCKS_METADATA.
                 */
                ext4_free_blocks(handle, inode, where[i].bh, 0, 1,
                                 EXT4_FREE_BLOCKS_FORGET);
        }
        ext4_free_blocks(handle, inode, 0, le32_to_cpu(where[num].key),
                         blks, 0);

        return err;
}

/*
 * The ext4_ind_map_blocks() function handles non-extents inodes
 * (i.e., using the traditional indirect/double-indirect i_blocks
 * scheme) for ext4_map_blocks().
 *
 * Allocation strategy is simple: if we have to allocate something, we will
 * have to go the whole way to leaf. So let's do it before attaching anything
 * to tree, set linkage between the newborn blocks, write them if sync is
 * required, recheck the path, free and repeat if check fails, otherwise
 * set the last missing link (that will protect us from any truncate-generated
 * removals - all blocks on the path are immune now) and possibly force the
 * write on the parent block.
 * That has a nice additional property: no special recovery from the failed
 * allocations is needed - we simply release blocks and do not touch anything
 * reachable from inode.
 *
 * `handle' can be NULL if create == 0.
 *
 * return > 0, # of blocks mapped or allocated.
 * return = 0, if plain lookup failed.
 * return < 0, error case.
 *
 * The ext4_ind_get_blocks() function should be called with
 * down_write(&EXT4_I(inode)->i_data_sem) if allocating filesystem
 * blocks (i.e., flags has EXT4_GET_BLOCKS_CREATE set) or
 * down_read(&EXT4_I(inode)->i_data_sem) if not allocating file system
 * blocks.
 */
static int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
                               struct ext4_map_blocks *map,
                               int flags)
{
        int err = -EIO;
        ext4_lblk_t offsets[4];
        Indirect chain[4];
        Indirect *partial;
        ext4_fsblk_t goal;
        int indirect_blks;
        int blocks_to_boundary = 0;
        int depth;
        int count = 0;
        ext4_fsblk_t first_block = 0;

        J_ASSERT(!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)));
        J_ASSERT(handle != NULL || (flags & EXT4_GET_BLOCKS_CREATE) == 0);
        depth = ext4_block_to_path(inode, map->m_lblk, offsets,
                                   &blocks_to_boundary);

        if (depth == 0)
                goto out;

        partial = ext4_get_branch(inode, depth, offsets, chain, &err);

        /* Simplest case - block found, no allocation needed */
        if (!partial) {
                first_block = le32_to_cpu(chain[depth - 1].key);
                count++;
                /*map more blocks*/
                while (count < map->m_len && count <= blocks_to_boundary) {
                        ext4_fsblk_t blk;

                        blk = le32_to_cpu(*(chain[depth-1].p + count));

                        if (blk == first_block + count)
                                count++;
                        else
                                break;
                }
                goto got_it;
        }

        /* Next simple case - plain lookup or failed read of indirect block */
        if ((flags & EXT4_GET_BLOCKS_CREATE) == 0 || err == -EIO)
                goto cleanup;

        /*
         * Okay, we need to do block allocation.
        */
        goal = ext4_find_goal(inode, map->m_lblk, partial);

        /* the number of blocks need to allocate for [d,t]indirect blocks */
        indirect_blks = (chain + depth) - partial - 1;

        /*
         * Next look up the indirect map to count the totoal number of
         * direct blocks to allocate for this branch.
         */
        count = ext4_blks_to_allocate(partial, indirect_blks,
                                      map->m_len, blocks_to_boundary);
        /*
         * Block out ext4_truncate while we alter the tree
         */
        err = ext4_alloc_branch(handle, inode, map->m_lblk, indirect_blks,
                                &count, goal,
                                offsets + (partial - chain), partial);

        /*
         * The ext4_splice_branch call will free and forget any buffers
         * on the new chain if there is a failure, but that risks using
         * up transaction credits, especially for bitmaps where the
         * credits cannot be returned.  Can we handle this somehow?  We
         * may need to return -EAGAIN upwards in the worst case.  --sct
         */
        if (!err)
                err = ext4_splice_branch(handle, inode, map->m_lblk,
                                         partial, indirect_blks, count);
        if (err)
                goto cleanup;

        map->m_flags |= EXT4_MAP_NEW;

        ext4_update_inode_fsync_trans(handle, inode, 1);
got_it:
        map->m_flags |= EXT4_MAP_MAPPED;
        map->m_pblk = le32_to_cpu(chain[depth-1].key);
        map->m_len = count;
        if (count > blocks_to_boundary)
                map->m_flags |= EXT4_MAP_BOUNDARY;
        err = count;
        /* Clean up and exit */
        partial = chain + depth - 1;    /* the whole chain */
cleanup:
        while (partial > chain) {
                BUFFER_TRACE(partial->bh, "call brelse");
                brelse(partial->bh);
                partial--;
        }
out:
        return err;
}

#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 new block at @lblocks for non extent file based file
 */
static int ext4_indirect_calc_metadata_amount(struct inode *inode,
                                              sector_t lblock)
{
        struct ext4_inode_info *ei = EXT4_I(inode);
        sector_t dind_mask = ~((sector_t)EXT4_ADDR_PER_BLOCK(inode->i_sb) - 1);
        int blk_bits;

        if (lblock < EXT4_NDIR_BLOCKS)
                return 0;

        lblock -= EXT4_NDIR_BLOCKS;

        if (ei->i_da_metadata_calc_len &&
            (lblock & dind_mask) == ei->i_da_metadata_calc_last_lblock) {
                ei->i_da_metadata_calc_len++;
                return 0;
        }
        ei->i_da_metadata_calc_last_lblock = lblock & dind_mask;
        ei->i_da_metadata_calc_len = 1;
        blk_bits = order_base_2(lblock);
        return (blk_bits / EXT4_ADDR_PER_BLOCK_BITS(inode->i_sb)) + 1;
}

/*
 * 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, sector_t lblock)
{
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                return ext4_ext_calc_metadata_amount(inode, lblock);

        return ext4_indirect_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);
        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\n",
                         __func__, inode->i_ino, used,
                         ei->i_reserved_data_blocks);
                WARN_ON(1);
                used = ei->i_reserved_data_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_dirtyblocks_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_dirtyblocks_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, 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, 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 casem, 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.
         */
        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, 0);
        } else {
                retval = ext4_ind_map_blocks(handle, inode, map, 0);
        }
        up_read((&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;
        }

        /* 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 th 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_I(inode)->i_delalloc_reserved_flag = 1;
        /*
         * 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_I(inode)->i_delalloc_reserved_flag = 0;

        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;

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

        if (flags && !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);

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

        bh = sb_getblk(inode->i_sb, map.m_pblk);
        if (!bh) {
                *errp = -EIO;
                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_META, 1, &bh);
        wait_on_buffer(bh);
        if (buffer_uptodate(bh))
                return bh;
        put_bh(bh);
        *err = -EIO;
        return NULL;
}

static int 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() ->
 * block_write_full_page(). 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.
 */
static 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;
}

/*
 * Truncate blocks that were not used by write. We have to truncate the
 * pagecache as well so that corresponding buffers get properly unmapped.
 */
static void ext4_truncate_failed_write(struct inode *inode)
{
        truncate_inode_pages(inode->i_mapping, inode->i_size);
        ext4_truncate(inode);
}

static int ext4_get_block_write(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;

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 = 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();

        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;
        }
        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;

        if (copied < len) {
                if (!PageUptodate(page))
                        copied = 0;
                page_zero_new_buffers(page, from+copied, to);
        }

        ret = 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);
        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 block located at lblock
 */
static int ext4_da_reserve_space(struct inode *inode, sector_t lblock)
{
        int retries = 0;
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct ext4_inode_info *ei = EXT4_I(inode);
        unsigned long md_needed;
        int 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);
        md_needed = ext4_calc_metadata_amount(inode, lblock);
        trace_ext4_da_reserve_space(inode, md_needed);
        spin_unlock(&ei->i_block_reservation_lock);

        /*
         * 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, 1);
        if (ret)
                return ret;
        /*
         * We do still charge estimated metadata to the sb though;
         * we cannot afford to run out of free blocks.
         */
        if (ext4_claim_free_blocks(sbi, md_needed + 1)) {
                dquot_release_reservation_block(inode, 1);
                if (ext4_should_retry_alloc(inode->i_sb, &retries)) {
                        yield();
                        goto repeat;
                }
                return -ENOSPC;
        }
        spin_lock(&ei->i_block_reservation_lock);
        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\n", 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.
                 */
                percpu_counter_sub(&sbi->s_dirtyblocks_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_dirtyblocks_counter, to_free);

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

        dquot_release_reservation_block(inode, 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;

        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);
        ext4_da_release_space(page->mapping->host, to_release);
}

/*
 * 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;
        int journal_data = ext4_should_journal_data(inode);
        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 commit_write = 0, redirty_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));

                        /*
                         * If the page does not have buffers (for
                         * whatever reason), try to create them using
                         * __block_write_begin.  If this fails,
                         * redirty the page and move on.
                         */
                        if (!page_has_buffers(page)) {
                                if (__block_write_begin(page, 0, len,
                                                noalloc_get_block_write)) {
                                redirty_page:
                                        redirty_page_for_writepage(mpd->wbc,
                                                                   page);
                                        unlock_page(page);
                                        continue;
                                }
                                commit_write = 1;
                        }

                        bh = page_bufs = page_buffers(page);
                        block_start = 0;
                        do {
                                if (!bh)
                                        goto redirty_page;
                                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);
                                }

                                /* redirty page if block allocation undone */
                                if (buffer_delay(bh) || buffer_unwritten(bh))
                                        redirty_page = 1;
                                bh = bh->b_this_page;
                                block_start += bh->b_size;
                                cur_logical++;
                                pblock++;
                        } while (bh != page_bufs);

                        if (redirty_page)
                                goto redirty_page;

                        if (commit_write)
                                /* mark the buffer_heads as dirty & uptodate */
                                block_commit_write(page, 0, len);

                        /*
                         * Delalloc doesn't support data journalling,
                         * but eventually maybe we'll lift this
                         * restriction.
                         */
                        if (unlikely(journal_data && PageChecked(page)))
                                err = __ext4_journalled_writepage(page, len);
                        else
                                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,
                                        sector_t logical, long blk_cnt)
{
        int nr_pages, i;
        pgoff_t index, end;
        struct pagevec pvec;
        struct inode *inode = mpd->inode;
        struct address_space *mapping = inode->i_mapping;

        index = logical >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
        end   = (logical + blk_cnt - 1) >>
                                (PAGE_CACHE_SHIFT - inode->i_blkbits);
        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);
        printk(KERN_CRIT "Total free blocks count %lld\n",
               ext4_count_free_blocks(inode->i_sb));
        printk(KERN_CRIT "Free/Dirty block details\n");
        printk(KERN_CRIT "free_blocks=%lld\n",
               (long long) percpu_counter_sum(&sbi->s_freeblocks_counter));
        printk(KERN_CRIT "dirty_blocks=%lld\n",
               (long long) percpu_counter_sum(&sbi->s_dirtyblocks_counter));
        printk(KERN_CRIT "Block reservation details\n");
        printk(KERN_CRIT "i_reserved_data_blocks=%u\n",
               EXT4_I(inode)->i_reserved_data_blocks);
        printk(KERN_CRIT "i_reserved_meta_blocks=%u\n",
               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 magic i_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 call
                 * ext4_writepage() for all of the pages which will
                 * just redirty the pages.
                 */
                if (err == -EAGAIN)
                        goto submit_io;

                if (err == -ENOSPC &&
                    ext4_count_free_blocks(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, next,
                                mpd->b_size >> mpd->inode->i_blkbits);
                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);
        }

        if (ext4_should_order_data(mpd->inode)) {
                err = ext4_jbd2_file_inode(handle, mpd->inode);
                if (err)
                        /* This only happens if the journal is aborted */
                        return;
        }

        /*
         * 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);
}

/*
 * __mpage_da_writepage - finds extent of pages and blocks
 *
 * @page: page to consider
 * @wbc: not used, we just follow rules
 * @data: context
 *
 * The function finds extents of pages and scan them for all blocks.
 */
static int __mpage_da_writepage(struct page *page,
                                struct writeback_control *wbc,
                                struct mpage_da_data *mpd)
{
        struct inode *inode = mpd->inode;
        struct buffer_head *bh, *head;
        sector_t logical;

        /*
         * Can we merge this page to current extent?
         */
        if (mpd->next_page != page->index) {
                /*
                 * Nope, we can't. So, we map non-allocated blocks
                 * and start IO on them
                 */
                if (mpd->next_page != mpd->first_page) {
                        mpage_da_map_and_submit(mpd);
                        /*
                         * skip rest of the page in the page_vec
                         */
                        redirty_page_for_writepage(wbc, page);
                        unlock_page(page);
                        return MPAGE_DA_EXTENT_TAIL;
                }

                /*
                 * Start next extent of pages ...
                 */
                mpd->first_page = page->index;

                /*
                 * ... and blocks
                 */
                mpd->b_size = 0;
                mpd->b_state = 0;
                mpd->b_blocknr = 0;
        }

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

        if (!page_has_buffers(page)) {
                mpage_add_bh_to_extent(mpd, logical, PAGE_CACHE_SIZE,
                                       (1 << BH_Dirty) | (1 << BH_Uptodate));
                if (mpd->io_done)
                        return MPAGE_DA_EXTENT_TAIL;
        } else {
                /*
                 * Page with regular buffer heads, just add all dirty ones
                 */
                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)
                                        return MPAGE_DA_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);
        }

        return 0;
}

/*
 * 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.
 */
static 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;
        sector_t invalid_block = ~((sector_t) 0xffff);

        if (invalid_block < ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es))
                invalid_block = ~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_map_blocks(NULL, inode, &map, 0);
        if (ret < 0)
                return ret;
        if (ret == 0) {
                if (buffer_delay(bh))
                        return 0; /* Not sure this could or should happen */
                /*
                 * XXX: __block_write_begin() unmaps passed block, is it OK?
                 */
                ret = ext4_da_reserve_space(inode, iblock);
                if (ret)
                        /* not enough space to reserve */
                        return ret;

                map_bh(bh, inode->i_sb, invalid_block);
                set_buffer_new(bh);
                set_buffer_delay(bh);
                return 0;
        }

        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;
}

/*
 * This function is used as a standard get_block_t calback function
 * when there is no desire to allocate any blocks.  It is used as a
 * callback function for block_write_begin() and block_write_full_page().
 * These functions should only try to map a single block at a time.
 *
 * Since this function doesn't do block allocations even if the caller
 * requests it by passing in create=1, it is critically important that
 * any caller checks to make sure that any buffer heads are returned
 * by this function are either all already mapped or marked for
 * delayed allocation before calling  block_write_full_page().  Otherwise,
 * b_blocknr could be left unitialized, and the page write functions will
 * be taken by surprise.
 */
static int noalloc_get_block_write(struct inode *inode, sector_t iblock,
                                   struct buffer_head *bh_result, int create)
{
        BUG_ON(bh_result->b_size != inode->i_sb->s_blocksize);
        return _ext4_get_block(inode, iblock, bh_result, 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;
        handle_t *handle = NULL;
        int ret = 0;
        int err;

        ClearPageChecked(page);
        page_bufs = page_buffers(page);
        BUG_ON(!page_bufs);
        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;
        }

        ret = walk_page_buffers(handle, page_bufs, 0, len, NULL,
                                do_journal_get_write_access);

        err = walk_page_buffers(handle, page_bufs, 0, len, NULL,
                                write_end_fn);
        if (ret == 0)
                ret = err;
        err = ext4_journal_stop(handle);
        if (!ret)
                ret = err;

        walk_page_buffers(handle, page_bufs, 0, len, NULL, bput_one);
        ext4_set_inode_state(inode, EXT4_STATE_JDATA);
out:
        return ret;
}

static int ext4_set_bh_endio(struct buffer_head *bh, struct inode *inode);
static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate);

/*
 * 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(), noone 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 pdflush (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 bufer_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, commit_write = 0;
        loff_t size;
        unsigned int len;
        struct buffer_head *page_bufs = NULL;
        struct inode *inode = page->mapping->host;

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

        /*
         * If the page does not have buffers (for whatever reason),
         * try to create them using __block_write_begin.  If this
         * fails, redirty the page and move on.
         */
        if (!page_has_buffers(page)) {
                if (__block_write_begin(page, 0, len,
                                        noalloc_get_block_write)) {
                redirty_page:
                        redirty_page_for_writepage(wbc, page);
                        unlock_page(page);
                        return 0;
                }
                commit_write = 1;
        }
        page_bufs = page_buffers(page);
        if (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
                 */
                goto redirty_page;
        }
        if (commit_write)
                /* now mark the buffer_heads as dirty and uptodate */
                block_commit_write(page, 0, len);

        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);

        if (buffer_uninit(page_bufs)) {
                ext4_set_bh_endio(page_bufs, inode);
                ret = block_write_full_page_endio(page, noalloc_get_block_write,
                                            wbc, ext4_end_io_buffer_write);
        } else
                ret = block_write_full_page(page, noalloc_get_block_write,
                                            wbc);

        return ret;
}

/*
 * This is called via ext4_da_writepages() to
 * calulate 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 call the callback function (which usually writes
 * the pages).
 *
 * This is a forked version of write_cache_pages().  Differences:
 *      Range cyclic is ignored.
 *      no_nrwrite_index_update is always presumed true
 */
static int write_cache_pages_da(struct address_space *mapping,
                                struct writeback_control *wbc,
                                struct mpage_da_data *mpd,
                                pgoff_t *done_index)
{
        int ret = 0;
        int done = 0;
        struct pagevec pvec;
        unsigned nr_pages;
        pgoff_t index;
        pgoff_t end;            /* Inclusive */
        long nr_to_write = wbc->nr_to_write;
        int tag;

        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)
                tag = PAGECACHE_TAG_TOWRITE;
        else
                tag = PAGECACHE_TAG_DIRTY;

        *done_index = index;
        while (!done && (index <= end)) {
                int i;

                nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
                              min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
                if (nr_pages == 0)
                        break;

                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) {
                                done = 1;
                                break;
                        }

                        *done_index = page->index + 1;

                        lock_page(page);

                        /*
                         * Page truncated or invalidated. We can freely skip it
                         * then, even for data integrity operations: the page
                         * has disappeared concurrently, so there could be no
                         * real expectation of this data interity operation
                         * even if there is now a new, dirty page at the same
                         * pagecache address.
                         */
                        if (unlikely(page->mapping != mapping)) {
continue_unlock:
                                unlock_page(page);
                                continue;
                        }

                        if (!PageDirty(page)) {
                                /* someone wrote it for us */
                                goto continue_unlock;
                        }

                        if (PageWriteback(page)) {
                                if (wbc->sync_mode != WB_SYNC_NONE)
                                        wait_on_page_writeback(page);
                                else
                                        goto continue_unlock;
                        }

                        BUG_ON(PageWriteback(page));
                        if (!clear_page_dirty_for_io(page))
                                goto continue_unlock;

                        ret = __mpage_da_writepage(page, wbc, mpd);
                        if (unlikely(ret)) {
                                if (ret == AOP_WRITEPAGE_ACTIVATE) {
                                        unlock_page(page);
                                        ret = 0;
                                } else {
                                        done = 1;
                                        break;
                                }
                        }

                        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.
                                         */
                                        done = 1;
                                        break;
                                }
                        }
                }
                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;
        long pages_skipped;
        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;

        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;
        }

        mpd.wbc = wbc;
        mpd.inode = mapping->host;

        pages_skipped = wbc->pages_skipped;

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

        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);
                        goto out_writepages;
                }

                /*
                 * Now call __mpage_da_writepage to find the next
                 * contiguous region of logical blocks that need
                 * blocks to be allocated by ext4.  We don't actually
                 * submit the blocks for I/O here, even though
                 * write_cache_pages thinks it will, and will set the
                 * pages as clean for write before calling
                 * __mpage_da_writepage().
                 */
                mpd.b_size = 0;
                mpd.b_state = 0;
                mpd.b_blocknr = 0;
                mpd.first_page = 0;
                mpd.next_page = 0;
                mpd.io_done = 0;
                mpd.pages_written = 0;
                mpd.retval = 0;
                ret = write_cache_pages_da(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);
                        wbc->pages_skipped = pages_skipped;
                        ret = 0;
                } else if (ret == MPAGE_DA_EXTENT_TAIL) {
                        /*
                         * got one extent now try with
                         * rest of the pages
                         */
                        pages_written += mpd.pages_written;
                        wbc->pages_skipped = pages_skipped;