fs/ntfs/aops.c

   1 /**
   2  * aops.c - NTFS kernel address space operations and page cache handling.
   3  *          Part of the Linux-NTFS project.
   4  *
   5  * Copyright (c) 2001-2005 Anton Altaparmakov
   6  * Copyright (c) 2002 Richard Russon
   7  *
   8  * This program/include file is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU General Public License as published
  10  * by the Free Software Foundation; either version 2 of the License, or
  11  * (at your option) any later version.
  12  *
  13  * This program/include file is distributed in the hope that it will be
  14  * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
  15  * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program (in the main directory of the Linux-NTFS
  20  * distribution in the file COPYING); if not, write to the Free Software
  21  * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  22  */
  23
  24 #include <linux/errno.h>
  25 #include <linux/mm.h>
  26 #include <linux/pagemap.h>
  27 #include <linux/swap.h>
  28 #include <linux/buffer_head.h>
  29 #include <linux/writeback.h>
  30 #include <linux/bit_spinlock.h>
  31
  32 #include "aops.h"
  33 #include "attrib.h"
  34 #include "debug.h"
  35 #include "inode.h"
  36 #include "mft.h"
  37 #include "runlist.h"
  38 #include "types.h"
  39 #include "ntfs.h"
  40
  41 /**
  42  * ntfs_end_buffer_async_read - async io completion for reading attributes
  43  * @bh:         buffer head on which io is completed
  44  * @uptodate:   whether @bh is now uptodate or not
  45  *
  46  * Asynchronous I/O completion handler for reading pages belonging to the
  47  * attribute address space of an inode.  The inodes can either be files or
  48  * directories or they can be fake inodes describing some attribute.
  49  *
  50  * If NInoMstProtected(), perform the post read mst fixups when all IO on the
  51  * page has been completed and mark the page uptodate or set the error bit on
  52  * the page.  To determine the size of the records that need fixing up, we
  53  * cheat a little bit by setting the index_block_size in ntfs_inode to the ntfs
  54  * record size, and index_block_size_bits, to the log(base 2) of the ntfs
  55  * record size.
  56  */
  57 static void ntfs_end_buffer_async_read(struct buffer_head *bh, int uptodate)
  58 {
  59         unsigned long flags;
  60         struct buffer_head *first, *tmp;
  61         struct page *page;
  62         ntfs_inode *ni;
  63         int page_uptodate = 1;
  64
  65         page = bh->b_page;
  66         ni = NTFS_I(page->mapping->host);
  67
  68         if (likely(uptodate)) {
  69                 s64 file_ofs, initialized_size;
  70
  71                 set_buffer_uptodate(bh);
  72
  73                 file_ofs = ((s64)page->index << PAGE_CACHE_SHIFT) +
  74                                 bh_offset(bh);
  75                 read_lock_irqsave(&ni->size_lock, flags);
  76                 initialized_size = ni->initialized_size;
  77                 read_unlock_irqrestore(&ni->size_lock, flags);
  78                 /* Check for the current buffer head overflowing. */
  79                 if (file_ofs + bh->b_size > initialized_size) {
  80                         char *addr;
  81                         int ofs = 0;
  82
  83                         if (file_ofs < initialized_size)
  84                                 ofs = initialized_size - file_ofs;
  85                         addr = kmap_atomic(page, KM_BIO_SRC_IRQ);
  86                         memset(addr + bh_offset(bh) + ofs, 0, bh->b_size - ofs);
  87                         flush_dcache_page(page);
  88                         kunmap_atomic(addr, KM_BIO_SRC_IRQ);
  89                 }
  90         } else {
  91                 clear_buffer_uptodate(bh);
  92                 SetPageError(page);
  93                 ntfs_error(ni->vol->sb, "Buffer I/O error, logical block %llu.",
  94                                 (unsigned long long)bh->b_blocknr);
  95         }
  96         first = page_buffers(page);
  97         local_irq_save(flags);
  98         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
  99         clear_buffer_async_read(bh);
 100         unlock_buffer(bh);
 101         tmp = bh;
 102         do {
 103                 if (!buffer_uptodate(tmp))
 104                         page_uptodate = 0;
 105                 if (buffer_async_read(tmp)) {
 106                         if (likely(buffer_locked(tmp)))
 107                                 goto still_busy;
 108                         /* Async buffers must be locked. */
 109                         BUG();
 110                 }
 111                 tmp = tmp->b_this_page;
 112         } while (tmp != bh);
 113         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 114         local_irq_restore(flags);
 115         /*
 116          * If none of the buffers had errors then we can set the page uptodate,
 117          * but we first have to perform the post read mst fixups, if the
 118          * attribute is mst protected, i.e. if NInoMstProteced(ni) is true.
 119          * Note we ignore fixup errors as those are detected when
 120          * map_mft_record() is called which gives us per record granularity
 121          * rather than per page granularity.
 122          */
 123         if (!NInoMstProtected(ni)) {
 124                 if (likely(page_uptodate && !PageError(page)))
 125                         SetPageUptodate(page);
 126         } else {
 127                 char *addr;
 128                 unsigned int i, recs;
 129                 u32 rec_size;
 130
 131                 rec_size = ni->itype.index.block_size;
 132                 recs = PAGE_CACHE_SIZE / rec_size;
 133                 /* Should have been verified before we got here... */
 134                 BUG_ON(!recs);
 135                 addr = kmap_atomic(page, KM_BIO_SRC_IRQ);
 136                 for (i = 0; i < recs; i++)
 137                         post_read_mst_fixup((NTFS_RECORD*)(addr +
 138                                         i * rec_size), rec_size);
 139                 flush_dcache_page(page);
 140                 kunmap_atomic(addr, KM_BIO_SRC_IRQ);
 141                 if (likely(page_uptodate && !PageError(page)))
 142                         SetPageUptodate(page);
 143         }
 144         unlock_page(page);
 145         return;
 146 still_busy:
 147         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 148         local_irq_restore(flags);
 149         return;
 150 }
 151
 152 /**
 153  * ntfs_read_block - fill a @page of an address space with data
 154  * @page:       page cache page to fill with data
 155  *
 156  * Fill the page @page of the address space belonging to the @page->host inode.
 157  * We read each buffer asynchronously and when all buffers are read in, our io
 158  * completion handler ntfs_end_buffer_read_async(), if required, automatically
 159  * applies the mst fixups to the page before finally marking it uptodate and
 160  * unlocking it.
 161  *
 162  * We only enforce allocated_size limit because i_size is checked for in
 163  * generic_file_read().
 164  *
 165  * Return 0 on success and -errno on error.
 166  *
 167  * Contains an adapted version of fs/buffer.c::block_read_full_page().
 168  */
 169 static int ntfs_read_block(struct page *page)
 170 {
 171         VCN vcn;
 172         LCN lcn;
 173         ntfs_inode *ni;
 174         ntfs_volume *vol;
 175         runlist_element *rl;
 176         struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
 177         sector_t iblock, lblock, zblock;
 178         unsigned long flags;
 179         unsigned int blocksize, vcn_ofs;
 180         int i, nr;
 181         unsigned char blocksize_bits;
 182
 183         ni = NTFS_I(page->mapping->host);
 184         vol = ni->vol;
 185
 186         /* $MFT/$DATA must have its complete runlist in memory at all times. */
 187         BUG_ON(!ni->runlist.rl && !ni->mft_no && !NInoAttr(ni));
 188
 189         blocksize_bits = VFS_I(ni)->i_blkbits;
 190         blocksize = 1 << blocksize_bits;
 191
 192         if (!page_has_buffers(page)) {
 193                 create_empty_buffers(page, blocksize, 0);
 194                 if (unlikely(!page_has_buffers(page))) {
 195                         unlock_page(page);
 196                         return -ENOMEM;
 197                 }
 198         }
 199         bh = head = page_buffers(page);
 200         BUG_ON(!bh);
 201
 202         iblock = (s64)page->index << (PAGE_CACHE_SHIFT - blocksize_bits);
 203         read_lock_irqsave(&ni->size_lock, flags);
 204         lblock = (ni->allocated_size + blocksize - 1) >> blocksize_bits;
 205         zblock = (ni->initialized_size + blocksize - 1) >> blocksize_bits;
 206         read_unlock_irqrestore(&ni->size_lock, flags);
 207
 208         /* Loop through all the buffers in the page. */
 209         rl = NULL;
 210         nr = i = 0;
 211         do {
 212                 u8 *kaddr;
 213                 int err;
 214
 215                 if (unlikely(buffer_uptodate(bh)))
 216                         continue;
 217                 if (unlikely(buffer_mapped(bh))) {
 218                         arr[nr++] = bh;
 219                         continue;
 220                 }
 221                 err = 0;
 222                 bh->b_bdev = vol->sb->s_bdev;
 223                 /* Is the block within the allowed limits? */
 224                 if (iblock < lblock) {
 225                         BOOL is_retry = FALSE;
 226
 227                         /* Convert iblock into corresponding vcn and offset. */
 228                         vcn = (VCN)iblock << blocksize_bits >>
 229                                         vol->cluster_size_bits;
 230                         vcn_ofs = ((VCN)iblock << blocksize_bits) &
 231                                         vol->cluster_size_mask;
 232                         if (!rl) {
 233 lock_retry_remap:
 234                                 down_read(&ni->runlist.lock);
 235                                 rl = ni->runlist.rl;
 236                         }
 237                         if (likely(rl != NULL)) {
 238                                 /* Seek to element containing target vcn. */
 239                                 while (rl->length && rl[1].vcn <= vcn)
 240                                         rl++;
 241                                 lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
 242                         } else
 243                                 lcn = LCN_RL_NOT_MAPPED;
 244                         /* Successful remap. */
 245                         if (lcn >= 0) {
 246                                 /* Setup buffer head to correct block. */
 247                                 bh->b_blocknr = ((lcn << vol->cluster_size_bits)
 248                                                 + vcn_ofs) >> blocksize_bits;
 249                                 set_buffer_mapped(bh);
 250                                 /* Only read initialized data blocks. */
 251                                 if (iblock < zblock) {
 252                                         arr[nr++] = bh;
 253                                         continue;
 254                                 }
 255                                 /* Fully non-initialized data block, zero it. */
 256                                 goto handle_zblock;
 257                         }
 258                         /* It is a hole, need to zero it. */
 259                         if (lcn == LCN_HOLE)
 260                                 goto handle_hole;
 261                         /* If first try and runlist unmapped, map and retry. */
 262                         if (!is_retry && lcn == LCN_RL_NOT_MAPPED) {
 263                                 is_retry = TRUE;
 264                                 /*
 265                                  * Attempt to map runlist, dropping lock for
 266                                  * the duration.
 267                                  */
 268                                 up_read(&ni->runlist.lock);
 269                                 err = ntfs_map_runlist(ni, vcn);
 270                                 if (likely(!err))
 271                                         goto lock_retry_remap;
 272                                 rl = NULL;
 273                         } else if (!rl)
 274                                 up_read(&ni->runlist.lock);
 275                         /*
 276                          * If buffer is outside the runlist, treat it as a
 277                          * hole.  This can happen due to concurrent truncate
 278                          * for example.
 279                          */
 280                         if (err == -ENOENT || lcn == LCN_ENOENT) {
 281                                 err = 0;
 282                                 goto handle_hole;
 283                         }
 284                         /* Hard error, zero out region. */
 285                         if (!err)
 286                                 err = -EIO;
 287                         bh->b_blocknr = -1;
 288                         SetPageError(page);
 289                         ntfs_error(vol->sb, "Failed to read from inode 0x%lx, "
 290                                         "attribute type 0x%x, vcn 0x%llx, "
 291                                         "offset 0x%x because its location on "
 292                                         "disk could not be determined%s "
 293                                         "(error code %i).", ni->mft_no,
 294                                         ni->type, (unsigned long long)vcn,
 295                                         vcn_ofs, is_retry ? " even after "
 296                                         "retrying" : "", err);
 297                 }
 298                 /*
 299                  * Either iblock was outside lblock limits or
 300                  * ntfs_rl_vcn_to_lcn() returned error.  Just zero that portion
 301                  * of the page and set the buffer uptodate.
 302                  */
 303 handle_hole:
 304                 bh->b_blocknr = -1UL;
 305                 clear_buffer_mapped(bh);
 306 handle_zblock:
 307                 kaddr = kmap_atomic(page, KM_USER0);
 308                 memset(kaddr + i * blocksize, 0, blocksize);
 309                 kunmap_atomic(kaddr, KM_USER0);
 310                 flush_dcache_page(page);
 311                 if (likely(!err))
 312                         set_buffer_uptodate(bh);
 313         } while (i++, iblock++, (bh = bh->b_this_page) != head);
 314
 315         /* Release the lock if we took it. */
 316         if (rl)
 317                 up_read(&ni->runlist.lock);
 318
 319         /* Check we have at least one buffer ready for i/o. */
 320         if (nr) {
 321                 struct buffer_head *tbh;
 322
 323                 /* Lock the buffers. */
 324                 for (i = 0; i < nr; i++) {
 325                         tbh = arr[i];
 326                         lock_buffer(tbh);
 327                         tbh->b_end_io = ntfs_end_buffer_async_read;
 328                         set_buffer_async_read(tbh);
 329                 }
 330                 /* Finally, start i/o on the buffers. */
 331                 for (i = 0; i < nr; i++) {
 332                         tbh = arr[i];
 333                         if (likely(!buffer_uptodate(tbh)))
 334                                 submit_bh(READ, tbh);
 335                         else
 336                                 ntfs_end_buffer_async_read(tbh, 1);
 337                 }
 338                 return 0;
 339         }
 340         /* No i/o was scheduled on any of the buffers. */
 341         if (likely(!PageError(page)))
 342                 SetPageUptodate(page);
 343         else /* Signal synchronous i/o error. */
 344                 nr = -EIO;
 345         unlock_page(page);
 346         return nr;
 347 }
 348
 349 /**
 350  * ntfs_readpage - fill a @page of a @file with data from the device
 351  * @file:       open file to which the page @page belongs or NULL
 352  * @page:       page cache page to fill with data
 353  *
 354  * For non-resident attributes, ntfs_readpage() fills the @page of the open
 355  * file @file by calling the ntfs version of the generic block_read_full_page()
 356  * function, ntfs_read_block(), which in turn creates and reads in the buffers
 357  * associated with the page asynchronously.
 358  *
 359  * For resident attributes, OTOH, ntfs_readpage() fills @page by copying the
 360  * data from the mft record (which at this stage is most likely in memory) and
 361  * fills the remainder with zeroes. Thus, in this case, I/O is synchronous, as
 362  * even if the mft record is not cached at this point in time, we need to wait
 363  * for it to be read in before we can do the copy.
 364  *
 365  * Return 0 on success and -errno on error.
 366  */
 367 static int ntfs_readpage(struct file *file, struct page *page)
 368 {
 369         ntfs_inode *ni, *base_ni;
 370         u8 *kaddr;
 371         ntfs_attr_search_ctx *ctx;
 372         MFT_RECORD *mrec;
 373         unsigned long flags;
 374         u32 attr_len;
 375         int err = 0;
 376
 377 retry_readpage:
 378         BUG_ON(!PageLocked(page));
 379         /*
 380          * This can potentially happen because we clear PageUptodate() during
 381          * ntfs_writepage() of MstProtected() attributes.
 382          */
 383         if (PageUptodate(page)) {
 384                 unlock_page(page);
 385                 return 0;
 386         }
 387         ni = NTFS_I(page->mapping->host);
 388         /*
 389          * Only $DATA attributes can be encrypted and only unnamed $DATA
 390          * attributes can be compressed.  Index root can have the flags set but
 391          * this means to create compressed/encrypted files, not that the
 392          * attribute is compressed/encrypted.  Note we need to check for
 393          * AT_INDEX_ALLOCATION since this is the type of both directory and
 394          * index inodes.
 395          */
 396         if (ni->type != AT_INDEX_ALLOCATION) {
 397                 /* If attribute is encrypted, deny access, just like NT4. */
 398                 if (NInoEncrypted(ni)) {
 399                         BUG_ON(ni->type != AT_DATA);
 400                         err = -EACCES;
 401                         goto err_out;
 402                 }
 403                 /* Compressed data streams are handled in compress.c. */
 404                 if (NInoNonResident(ni) && NInoCompressed(ni)) {
 405                         BUG_ON(ni->type != AT_DATA);
 406                         BUG_ON(ni->name_len);
 407                         return ntfs_read_compressed_block(page);
 408                 }
 409         }
 410         /* NInoNonResident() == NInoIndexAllocPresent() */
 411         if (NInoNonResident(ni)) {
 412                 /* Normal, non-resident data stream. */
 413                 return ntfs_read_block(page);
 414         }
 415         /*
 416          * Attribute is resident, implying it is not compressed or encrypted.
 417          * This also means the attribute is smaller than an mft record and
 418          * hence smaller than a page, so can simply zero out any pages with
 419          * index above 0.  Note the attribute can actually be marked compressed
 420          * but if it is resident the actual data is not compressed so we are
 421          * ok to ignore the compressed flag here.
 422          */
 423         if (unlikely(page->index > 0)) {
 424                 kaddr = kmap_atomic(page, KM_USER0);
 425                 memset(kaddr, 0, PAGE_CACHE_SIZE);
 426                 flush_dcache_page(page);
 427                 kunmap_atomic(kaddr, KM_USER0);
 428                 goto done;
 429         }
 430         if (!NInoAttr(ni))
 431                 base_ni = ni;
 432         else
 433                 base_ni = ni->ext.base_ntfs_ino;
 434         /* Map, pin, and lock the mft record. */
 435         mrec = map_mft_record(base_ni);
 436         if (IS_ERR(mrec)) {
 437                 err = PTR_ERR(mrec);
 438                 goto err_out;
 439         }
 440         /*
 441          * If a parallel write made the attribute non-resident, drop the mft
 442          * record and retry the readpage.
 443          */
 444         if (unlikely(NInoNonResident(ni))) {
 445                 unmap_mft_record(base_ni);
 446                 goto retry_readpage;
 447         }
 448         ctx = ntfs_attr_get_search_ctx(base_ni, mrec);
 449         if (unlikely(!ctx)) {
 450                 err = -ENOMEM;
 451                 goto unm_err_out;
 452         }
 453         err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
 454                         CASE_SENSITIVE, 0, NULL, 0, ctx);
 455         if (unlikely(err))
 456                 goto put_unm_err_out;
 457         attr_len = le32_to_cpu(ctx->attr->data.resident.value_length);
 458         read_lock_irqsave(&ni->size_lock, flags);
 459         if (unlikely(attr_len > ni->initialized_size))
 460                 attr_len = ni->initialized_size;
 461         read_unlock_irqrestore(&ni->size_lock, flags);
 462         kaddr = kmap_atomic(page, KM_USER0);
 463         /* Copy the data to the page. */
 464         memcpy(kaddr, (u8*)ctx->attr +
 465                         le16_to_cpu(ctx->attr->data.resident.value_offset),
 466                         attr_len);
 467         /* Zero the remainder of the page. */
 468         memset(kaddr + attr_len, 0, PAGE_CACHE_SIZE - attr_len);
 469         flush_dcache_page(page);
 470         kunmap_atomic(kaddr, KM_USER0);
 471 put_unm_err_out:
 472         ntfs_attr_put_search_ctx(ctx);
 473 unm_err_out:
 474         unmap_mft_record(base_ni);
 475 done:
 476         SetPageUptodate(page);
 477 err_out:
 478         unlock_page(page);
 479         return err;
 480 }
 481
 482 #ifdef NTFS_RW
 483
 484 /**
 485  * ntfs_write_block - write a @page to the backing store
 486  * @page:       page cache page to write out
 487  * @wbc:        writeback control structure
 488  *
 489  * This function is for writing pages belonging to non-resident, non-mst
 490  * protected attributes to their backing store.
 491  *
 492  * For a page with buffers, map and write the dirty buffers asynchronously
 493  * under page writeback. For a page without buffers, create buffers for the
 494  * page, then proceed as above.
 495  *
 496  * If a page doesn't have buffers the page dirty state is definitive. If a page
 497  * does have buffers, the page dirty state is just a hint, and the buffer dirty
 498  * state is definitive. (A hint which has rules: dirty buffers against a clean
 499  * page is illegal. Other combinations are legal and need to be handled. In
 500  * particular a dirty page containing clean buffers for example.)
 501  *
 502  * Return 0 on success and -errno on error.
 503  *
 504  * Based on ntfs_read_block() and __block_write_full_page().
 505  */
 506 static int ntfs_write_block(struct page *page, struct writeback_control *wbc)
 507 {
 508         VCN vcn;
 509         LCN lcn;
 510         s64 initialized_size;
 511         loff_t i_size;
 512         sector_t block, dblock, iblock;
 513         struct inode *vi;
 514         ntfs_inode *ni;
 515         ntfs_volume *vol;
 516         runlist_element *rl;
 517         struct buffer_head *bh, *head;
 518         unsigned long flags;
 519         unsigned int blocksize, vcn_ofs;
 520         int err;
 521         BOOL need_end_writeback;
 522         unsigned char blocksize_bits;
 523
 524         vi = page->mapping->host;
 525         ni = NTFS_I(vi);
 526         vol = ni->vol;
 527
 528         ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
 529                         "0x%lx.", ni->mft_no, ni->type, page->index);
 530
 531         BUG_ON(!NInoNonResident(ni));
 532         BUG_ON(NInoMstProtected(ni));
 533
 534         blocksize_bits = vi->i_blkbits;
 535         blocksize = 1 << blocksize_bits;
 536
 537         if (!page_has_buffers(page)) {
 538                 BUG_ON(!PageUptodate(page));
 539                 create_empty_buffers(page, blocksize,
 540                                 (1 << BH_Uptodate) | (1 << BH_Dirty));
 541                 if (unlikely(!page_has_buffers(page))) {
 542                         ntfs_warning(vol->sb, "Error allocating page "
 543                                         "buffers.  Redirtying page so we try "
 544                                         "again later.");
 545                         /*
 546                          * Put the page back on mapping->dirty_pages, but leave
 547                          * its buffers' dirty state as-is.
 548                          */
 549                         redirty_page_for_writepage(wbc, page);
 550                         unlock_page(page);
 551                         return 0;
 552                 }
 553         }
 554         bh = head = page_buffers(page);
 555         BUG_ON(!bh);
 556
 557         /* NOTE: Different naming scheme to ntfs_read_block()! */
 558
 559         /* The first block in the page. */
 560         block = (s64)page->index << (PAGE_CACHE_SHIFT - blocksize_bits);
 561
 562         read_lock_irqsave(&ni->size_lock, flags);
 563         i_size = i_size_read(vi);
 564         initialized_size = ni->initialized_size;
 565         read_unlock_irqrestore(&ni->size_lock, flags);
 566
 567         /* The first out of bounds block for the data size. */
 568         dblock = (i_size + blocksize - 1) >> blocksize_bits;
 569
 570         /* The last (fully or partially) initialized block. */
 571         iblock = initialized_size >> blocksize_bits;
 572
 573         /*
 574          * Be very careful.  We have no exclusion from __set_page_dirty_buffers
 575          * here, and the (potentially unmapped) buffers may become dirty at
 576          * any time.  If a buffer becomes dirty here after we've inspected it
 577          * then we just miss that fact, and the page stays dirty.
 578          *
 579          * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
 580          * handle that here by just cleaning them.
 581          */
 582
 583         /*
 584          * Loop through all the buffers in the page, mapping all the dirty
 585          * buffers to disk addresses and handling any aliases from the
 586          * underlying block device's mapping.
 587          */
 588         rl = NULL;
 589         err = 0;
 590         do {
 591                 BOOL is_retry = FALSE;
 592
 593                 if (unlikely(block >= dblock)) {
 594                         /*
 595                          * Mapped buffers outside i_size will occur, because
 596                          * this page can be outside i_size when there is a
 597                          * truncate in progress. The contents of such buffers
 598                          * were zeroed by ntfs_writepage().
 599                          *
 600                          * FIXME: What about the small race window where
 601                          * ntfs_writepage() has not done any clearing because
 602                          * the page was within i_size but before we get here,
 603                          * vmtruncate() modifies i_size?
 604                          */
 605                         clear_buffer_dirty(bh);
 606                         set_buffer_uptodate(bh);
 607                         continue;
 608                 }
 609
 610                 /* Clean buffers are not written out, so no need to map them. */
 611                 if (!buffer_dirty(bh))
 612                         continue;
 613
 614                 /* Make sure we have enough initialized size. */
 615                 if (unlikely((block >= iblock) &&
 616                                 (initialized_size < i_size))) {
 617                         /*
 618                          * If this page is fully outside initialized size, zero
 619                          * out all pages between the current initialized size
 620                          * and the current page. Just use ntfs_readpage() to do
 621                          * the zeroing transparently.
 622                          */
 623                         if (block > iblock) {
 624                                 // TODO:
 625                                 // For each page do:
 626                                 // - read_cache_page()
 627                                 // Again for each page do:
 628                                 // - wait_on_page_locked()
 629                                 // - Check (PageUptodate(page) &&
 630                                 //                      !PageError(page))
 631                                 // Update initialized size in the attribute and
 632                                 // in the inode.
 633                                 // Again, for each page do:
 634                                 //      __set_page_dirty_buffers();
 635                                 // page_cache_release()
 636                                 // We don't need to wait on the writes.
 637                                 // Update iblock.
 638                         }
 639                         /*
 640                          * The current page straddles initialized size. Zero
 641                          * all non-uptodate buffers and set them uptodate (and
 642                          * dirty?). Note, there aren't any non-uptodate buffers
 643                          * if the page is uptodate.
 644                          * FIXME: For an uptodate page, the buffers may need to
 645                          * be written out because they were not initialized on
 646                          * disk before.
 647                          */
 648                         if (!PageUptodate(page)) {
 649                                 // TODO:
 650                                 // Zero any non-uptodate buffers up to i_size.
 651                                 // Set them uptodate and dirty.
 652                         }
 653                         // TODO:
 654                         // Update initialized size in the attribute and in the
 655                         // inode (up to i_size).
 656                         // Update iblock.
 657                         // FIXME: This is inefficient. Try to batch the two
 658                         // size changes to happen in one go.
 659                         ntfs_error(vol->sb, "Writing beyond initialized size "
 660                                         "is not supported yet. Sorry.");
 661                         err = -EOPNOTSUPP;
 662                         break;
 663                         // Do NOT set_buffer_new() BUT DO clear buffer range
 664                         // outside write request range.
 665                         // set_buffer_uptodate() on complete buffers as well as
 666                         // set_buffer_dirty().
 667                 }
 668
 669                 /* No need to map buffers that are already mapped. */
 670                 if (buffer_mapped(bh))
 671                         continue;
 672
 673                 /* Unmapped, dirty buffer. Need to map it. */
 674                 bh->b_bdev = vol->sb->s_bdev;
 675
 676                 /* Convert block into corresponding vcn and offset. */
 677                 vcn = (VCN)block << blocksize_bits;
 678                 vcn_ofs = vcn & vol->cluster_size_mask;
 679                 vcn >>= vol->cluster_size_bits;
 680                 if (!rl) {
 681 lock_retry_remap:
 682                         down_read(&ni->runlist.lock);
 683                         rl = ni->runlist.rl;
 684                 }
 685                 if (likely(rl != NULL)) {
 686                         /* Seek to element containing target vcn. */
 687                         while (rl->length && rl[1].vcn <= vcn)
 688                                 rl++;
 689                         lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
 690                 } else
 691                         lcn = LCN_RL_NOT_MAPPED;
 692                 /* Successful remap. */
 693                 if (lcn >= 0) {
 694                         /* Setup buffer head to point to correct block. */
 695                         bh->b_blocknr = ((lcn << vol->cluster_size_bits) +
 696                                         vcn_ofs) >> blocksize_bits;
 697                         set_buffer_mapped(bh);
 698                         continue;
 699                 }
 700                 /* It is a hole, need to instantiate it. */
 701                 if (lcn == LCN_HOLE) {
 702                         u8 *kaddr;
 703                         unsigned long *bpos, *bend;
 704
 705                         /* Check if the buffer is zero. */
 706                         kaddr = kmap_atomic(page, KM_USER0);
 707                         bpos = (unsigned long *)(kaddr + bh_offset(bh));
 708                         bend = (unsigned long *)((u8*)bpos + blocksize);
 709                         do {
 710                                 if (unlikely(*bpos))
 711                                         break;
 712                         } while (likely(++bpos < bend));
 713                         kunmap_atomic(kaddr, KM_USER0);
 714                         if (bpos == bend) {
 715                                 /*
 716                                  * Buffer is zero and sparse, no need to write
 717                                  * it.
 718                                  */
 719                                 bh->b_blocknr = -1;
 720                                 clear_buffer_dirty(bh);
 721                                 continue;
 722                         }
 723                         // TODO: Instantiate the hole.
 724                         // clear_buffer_new(bh);
 725                         // unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
 726                         ntfs_error(vol->sb, "Writing into sparse regions is "
 727                                         "not supported yet. Sorry.");
 728                         err = -EOPNOTSUPP;
 729                         break;
 730                 }
 731                 /* If first try and runlist unmapped, map and retry. */
 732                 if (!is_retry && lcn == LCN_RL_NOT_MAPPED) {
 733                         is_retry = TRUE;
 734                         /*
 735                          * Attempt to map runlist, dropping lock for
 736                          * the duration.
 737                          */
 738                         up_read(&ni->runlist.lock);
 739                         err = ntfs_map_runlist(ni, vcn);
 740                         if (likely(!err))
 741                                 goto lock_retry_remap;
 742                         rl = NULL;
 743                 } else if (!rl)
 744                         up_read(&ni->runlist.lock);
 745                 /*
 746                  * If buffer is outside the runlist, truncate has cut it out
 747                  * of the runlist.  Just clean and clear the buffer and set it
 748                  * uptodate so it can get discarded by the VM.
 749                  */
 750                 if (err == -ENOENT || lcn == LCN_ENOENT) {
 751                         u8 *kaddr;
 752
 753                         bh->b_blocknr = -1;
 754                         clear_buffer_dirty(bh);
 755                         kaddr = kmap_atomic(page, KM_USER0);
 756                         memset(kaddr + bh_offset(bh), 0, blocksize);
 757                         kunmap_atomic(kaddr, KM_USER0);
 758                         flush_dcache_page(page);
 759                         set_buffer_uptodate(bh);
 760                         err = 0;
 761                         continue;
 762                 }
 763                 /* Failed to map the buffer, even after retrying. */
 764                 if (!err)
 765                         err = -EIO;
 766                 bh->b_blocknr = -1;
 767                 ntfs_error(vol->sb, "Failed to write to inode 0x%lx, "
 768                                 "attribute type 0x%x, vcn 0x%llx, offset 0x%x "
 769                                 "because its location on disk could not be "
 770                                 "determined%s (error code %i).", ni->mft_no,
 771                                 ni->type, (unsigned long long)vcn,
 772                                 vcn_ofs, is_retry ? " even after "
 773                                 "retrying" : "", err);
 774                 break;
 775         } while (block++, (bh = bh->b_this_page) != head);
 776
 777         /* Release the lock if we took it. */
 778         if (rl)
 779                 up_read(&ni->runlist.lock);
 780
 781         /* For the error case, need to reset bh to the beginning. */
 782         bh = head;
 783
 784         /* Just an optimization, so ->readpage() is not called later. */
 785         if (unlikely(!PageUptodate(page))) {
 786                 int uptodate = 1;
 787                 do {
 788                         if (!buffer_uptodate(bh)) {
 789                                 uptodate = 0;
 790                                 bh = head;
 791                                 break;
 792                         }
 793                 } while ((bh = bh->b_this_page) != head);
 794                 if (uptodate)
 795                         SetPageUptodate(page);
 796         }
 797
 798         /* Setup all mapped, dirty buffers for async write i/o. */
 799         do {
 800                 if (buffer_mapped(bh) && buffer_dirty(bh)) {
 801                         lock_buffer(bh);
 802                         if (test_clear_buffer_dirty(bh)) {
 803                                 BUG_ON(!buffer_uptodate(bh));
 804                                 mark_buffer_async_write(bh);
 805                         } else
 806                                 unlock_buffer(bh);
 807                 } else if (unlikely(err)) {
 808                         /*
 809                          * For the error case. The buffer may have been set
 810                          * dirty during attachment to a dirty page.
 811                          */
 812                         if (err != -ENOMEM)
 813                                 clear_buffer_dirty(bh);
 814                 }
 815         } while ((bh = bh->b_this_page) != head);
 816
 817         if (unlikely(err)) {
 818                 // TODO: Remove the -EOPNOTSUPP check later on...
 819                 if (unlikely(err == -EOPNOTSUPP))
 820                         err = 0;
 821                 else if (err == -ENOMEM) {
 822                         ntfs_warning(vol->sb, "Error allocating memory. "
 823                                         "Redirtying page so we try again "
 824                                         "later.");
 825                         /*
 826                          * Put the page back on mapping->dirty_pages, but
 827                          * leave its buffer's dirty state as-is.
 828                          */
 829                         redirty_page_for_writepage(wbc, page);
 830                         err = 0;
 831                 } else
 832                         SetPageError(page);
 833         }
 834
 835         BUG_ON(PageWriteback(page));
 836         set_page_writeback(page);       /* Keeps try_to_free_buffers() away. */
 837
 838         /* Submit the prepared buffers for i/o. */
 839         need_end_writeback = TRUE;
 840         do {
 841                 struct buffer_head *next = bh->b_this_page;
 842                 if (buffer_async_write(bh)) {
 843                         submit_bh(WRITE, bh);
 844                         need_end_writeback = FALSE;
 845                 }
 846                 bh = next;
 847         } while (bh != head);
 848         unlock_page(page);
 849
 850         /* If no i/o was started, need to end_page_writeback(). */
 851         if (unlikely(need_end_writeback))
 852                 end_page_writeback(page);
 853
 854         ntfs_debug("Done.");
 855         return err;
 856 }
 857
 858 /**
 859  * ntfs_write_mst_block - write a @page to the backing store
 860  * @page:       page cache page to write out
 861  * @wbc:        writeback control structure
 862  *
 863  * This function is for writing pages belonging to non-resident, mst protected
 864  * attributes to their backing store.  The only supported attributes are index
 865  * allocation and $MFT/$DATA.  Both directory inodes and index inodes are
 866  * supported for the index allocation case.
 867  *
 868  * The page must remain locked for the duration of the write because we apply
 869  * the mst fixups, write, and then undo the fixups, so if we were to unlock the
 870  * page before undoing the fixups, any other user of the page will see the
 871  * page contents as corrupt.
 872  *
 873  * We clear the page uptodate flag for the duration of the function to ensure
 874  * exclusion for the $MFT/$DATA case against someone mapping an mft record we
 875  * are about to apply the mst fixups to.
 876  *
 877  * Return 0 on success and -errno on error.
 878  *
 879  * Based on ntfs_write_block(), ntfs_mft_writepage(), and
 880  * write_mft_record_nolock().
 881  */
 882 static int ntfs_write_mst_block(struct page *page,
 883                 struct writeback_control *wbc)
 884 {
 885         sector_t block, dblock, rec_block;
 886         struct inode *vi = page->mapping->host;
 887         ntfs_inode *ni = NTFS_I(vi);
 888         ntfs_volume *vol = ni->vol;
 889         u8 *kaddr;
 890         unsigned int rec_size = ni->itype.index.block_size;
 891         ntfs_inode *locked_nis[PAGE_CACHE_SIZE / rec_size];
 892         struct buffer_head *bh, *head, *tbh, *rec_start_bh;
 893         struct buffer_head *bhs[MAX_BUF_PER_PAGE];
 894         runlist_element *rl;
 895         int i, nr_locked_nis, nr_recs, nr_bhs, max_bhs, bhs_per_rec, err, err2;
 896         unsigned bh_size, rec_size_bits;
 897         BOOL sync, is_mft, page_is_dirty, rec_is_dirty;
 898         unsigned char bh_size_bits;
 899
 900         ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
 901                         "0x%lx.", vi->i_ino, ni->type, page->index);
 902         BUG_ON(!NInoNonResident(ni));
 903         BUG_ON(!NInoMstProtected(ni));
 904         is_mft = (S_ISREG(vi->i_mode) && !vi->i_ino);
 905         /*
 906          * NOTE: ntfs_write_mst_block() would be called for $MFTMirr if a page
 907          * in its page cache were to be marked dirty.  However this should
 908          * never happen with the current driver and considering we do not
 909          * handle this case here we do want to BUG(), at least for now.
 910          */
 911         BUG_ON(!(is_mft || S_ISDIR(vi->i_mode) ||
 912                         (NInoAttr(ni) && ni->type == AT_INDEX_ALLOCATION)));
 913         bh_size_bits = vi->i_blkbits;
 914         bh_size = 1 << bh_size_bits;
 915         max_bhs = PAGE_CACHE_SIZE / bh_size;
 916         BUG_ON(!max_bhs);
 917         BUG_ON(max_bhs > MAX_BUF_PER_PAGE);
 918
 919         /* Were we called for sync purposes? */
 920         sync = (wbc->sync_mode == WB_SYNC_ALL);
 921
 922         /* Make sure we have mapped buffers. */
 923         bh = head = page_buffers(page);
 924         BUG_ON(!bh);
 925
 926         rec_size_bits = ni->itype.index.block_size_bits;
 927         BUG_ON(!(PAGE_CACHE_SIZE >> rec_size_bits));
 928         bhs_per_rec = rec_size >> bh_size_bits;
 929         BUG_ON(!bhs_per_rec);
 930
 931         /* The first block in the page. */
 932         rec_block = block = (sector_t)page->index <<
 933                         (PAGE_CACHE_SHIFT - bh_size_bits);
 934
 935         /* The first out of bounds block for the data size. */
 936         dblock = (i_size_read(vi) + bh_size - 1) >> bh_size_bits;
 937
 938         rl = NULL;
 939         err = err2 = nr_bhs = nr_recs = nr_locked_nis = 0;
 940         page_is_dirty = rec_is_dirty = FALSE;
 941         rec_start_bh = NULL;
 942         do {
 943                 BOOL is_retry = FALSE;
 944
 945                 if (likely(block < rec_block)) {
 946                         if (unlikely(block >= dblock)) {
 947                                 clear_buffer_dirty(bh);
 948                                 set_buffer_uptodate(bh);
 949                                 continue;
 950                         }
 951                         /*
 952                          * This block is not the first one in the record.  We
 953                          * ignore the buffer's dirty state because we could
 954                          * have raced with a parallel mark_ntfs_record_dirty().
 955                          */
 956                         if (!rec_is_dirty)
 957                                 continue;
 958                         if (unlikely(err2)) {
 959                                 if (err2 != -ENOMEM)
 960                                         clear_buffer_dirty(bh);
 961                                 continue;
 962                         }
 963                 } else /* if (block == rec_block) */ {
 964                         BUG_ON(block > rec_block);
 965                         /* This block is the first one in the record. */
 966                         rec_block += bhs_per_rec;
 967                         err2 = 0;
 968                         if (unlikely(block >= dblock)) {
 969                                 clear_buffer_dirty(bh);
 970                                 continue;
 971                         }
 972                         if (!buffer_dirty(bh)) {
 973                                 /* Clean records are not written out. */
 974                                 rec_is_dirty = FALSE;
 975                                 continue;
 976                         }
 977                         rec_is_dirty = TRUE;
 978                         rec_start_bh = bh;
 979                 }
 980                 /* Need to map the buffer if it is not mapped already. */
 981                 if (unlikely(!buffer_mapped(bh))) {
 982                         VCN vcn;
 983                         LCN lcn;
 984                         unsigned int vcn_ofs;
 985
 986                         bh->b_bdev = vol->sb->s_bdev;
 987                         /* Obtain the vcn and offset of the current block. */
 988                         vcn = (VCN)block << bh_size_bits;
 989                         vcn_ofs = vcn & vol->cluster_size_mask;
 990                         vcn >>= vol->cluster_size_bits;
 991                         if (!rl) {
 992 lock_retry_remap:
 993                                 down_read(&ni->runlist.lock);
 994                                 rl = ni->runlist.rl;
 995                         }
 996                         if (likely(rl != NULL)) {
 997                                 /* Seek to element containing target vcn. */
 998                                 while (rl->length && rl[1].vcn <= vcn)
 999                                         rl++;
1000                                 lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
1001                         } else
1002                                 lcn = LCN_RL_NOT_MAPPED;
1003                         /* Successful remap. */
1004                         if (likely(lcn >= 0)) {
1005                                 /* Setup buffer head to correct block. */
1006                                 bh->b_blocknr = ((lcn <<
1007                                                 vol->cluster_size_bits) +
1008                                                 vcn_ofs) >> bh_size_bits;
1009                                 set_buffer_mapped(bh);
1010                         } else {
1011                                 /*
1012                                  * Remap failed.  Retry to map the runlist once
1013                                  * unless we are working on $MFT which always
1014                                  * has the whole of its runlist in memory.
1015                                  */
1016                                 if (!is_mft && !is_retry &&
1017                                                 lcn == LCN_RL_NOT_MAPPED) {
1018                                         is_retry = TRUE;
1019                                         /*
1020                                          * Attempt to map runlist, dropping
1021                                          * lock for the duration.
1022                                          */
1023                                         up_read(&ni->runlist.lock);
1024                                         err2 = ntfs_map_runlist(ni, vcn);
1025                                         if (likely(!err2))
1026                                                 goto lock_retry_remap;
1027                                         if (err2 == -ENOMEM)
1028                                                 page_is_dirty = TRUE;
1029                                         lcn = err2;
1030                                 } else {
1031                                         err2 = -EIO;
1032                                         if (!rl)
1033                                                 up_read(&ni->runlist.lock);
1034                                 }
1035                                 /* Hard error.  Abort writing this record. */
1036                                 if (!err || err == -ENOMEM)
1037                                         err = err2;
1038                                 bh->b_blocknr = -1;
1039                                 ntfs_error(vol->sb, "Cannot write ntfs record "
1040                                                 "0x%llx (inode 0x%lx, "
1041                                                 "attribute type 0x%x) because "
1042                                                 "its location on disk could "
1043                                                 "not be determined (error "
1044                                                 "code %lli).",
1045                                                 (long long)block <<
1046                                                 bh_size_bits >>
1047                                                 vol->mft_record_size_bits,
1048                                                 ni->mft_no, ni->type,
1049                                                 (long long)lcn);
1050                                 /*
1051                                  * If this is not the first buffer, remove the
1052                                  * buffers in this record from the list of
1053                                  * buffers to write and clear their dirty bit
1054                                  * if not error -ENOMEM.
1055                                  */
1056                                 if (rec_start_bh != bh) {
1057                                         while (bhs[--nr_bhs] != rec_start_bh)
1058                                                 ;
1059                                         if (err2 != -ENOMEM) {
1060                                                 do {
1061                                                         clear_buffer_dirty(
1062                                                                 rec_start_bh);
1063                                                 } while ((rec_start_bh =
1064                                                                 rec_start_bh->
1065                                                                 b_this_page) !=
1066                                                                 bh);
1067                                         }
1068                                 }
1069                                 continue;
1070                         }
1071                 }
1072                 BUG_ON(!buffer_uptodate(bh));
1073                 BUG_ON(nr_bhs >= max_bhs);
1074                 bhs[nr_bhs++] = bh;
1075         } while (block++, (bh = bh->b_this_page) != head);
1076         if (unlikely(rl))
1077                 up_read(&ni->runlist.lock);
1078         /* If there were no dirty buffers, we are done. */
1079         if (!nr_bhs)
1080                 goto done;
1081         /* Map the page so we can access its contents. */
1082         kaddr = kmap(page);
1083         /* Clear the page uptodate flag whilst the mst fixups are applied. */
1084         BUG_ON(!PageUptodate(page));
1085         ClearPageUptodate(page);
1086         for (i = 0; i < nr_bhs; i++) {
1087                 unsigned int ofs;
1088
1089                 /* Skip buffers which are not at the beginning of records. */
1090                 if (i % bhs_per_rec)
1091                         continue;
1092                 tbh = bhs[i];
1093                 ofs = bh_offset(tbh);
1094                 if (is_mft) {
1095                         ntfs_inode *tni;
1096                         unsigned long mft_no;
1097
1098                         /* Get the mft record number. */
1099                         mft_no = (((s64)page->index << PAGE_CACHE_SHIFT) + ofs)
1100                                         >> rec_size_bits;
1101                         /* Check whether to write this mft record. */
1102                         tni = NULL;
1103                         if (!ntfs_may_write_mft_record(vol, mft_no,
1104                                         (MFT_RECORD*)(kaddr + ofs), &tni)) {
1105                                 /*
1106                                  * The record should not be written.  This
1107                                  * means we need to redirty the page before
1108                                  * returning.
1109                                  */
1110                                 page_is_dirty = TRUE;
1111                                 /*
1112                                  * Remove the buffers in this mft record from
1113                                  * the list of buffers to write.
1114                                  */
1115                                 do {
1116                                         bhs[i] = NULL;
1117                                 } while (++i % bhs_per_rec);
1118                                 continue;
1119                         }
1120                         /*
1121                          * The record should be written.  If a locked ntfs
1122                          * inode was returned, add it to the array of locked
1123                          * ntfs inodes.
1124                          */
1125                         if (tni)
1126                                 locked_nis[nr_locked_nis++] = tni;
1127                 }
1128                 /* Apply the mst protection fixups. */
1129                 err2 = pre_write_mst_fixup((NTFS_RECORD*)(kaddr + ofs),
1130                                 rec_size);
1131                 if (unlikely(err2)) {
1132                         if (!err || err == -ENOMEM)
1133                                 err = -EIO;
1134                         ntfs_error(vol->sb, "Failed to apply mst fixups "
1135                                         "(inode 0x%lx, attribute type 0x%x, "
1136                                         "page index 0x%lx, page offset 0x%x)!"
1137                                         "  Unmount and run chkdsk.", vi->i_ino,
1138                                         ni->type, page->index, ofs);
1139                         /*
1140                          * Mark all the buffers in this record clean as we do
1141                          * not want to write corrupt data to disk.
1142                          */
1143                         do {
1144                                 clear_buffer_dirty(bhs[i]);
1145                                 bhs[i] = NULL;
1146                         } while (++i % bhs_per_rec);
1147                         continue;
1148                 }
1149                 nr_recs++;
1150         }
1151         /* If no records are to be written out, we are done. */
1152         if (!nr_recs)
1153                 goto unm_done;
1154         flush_dcache_page(page);
1155         /* Lock buffers and start synchronous write i/o on them. */
1156         for (i = 0; i < nr_bhs; i++) {
1157                 tbh = bhs[i];
1158                 if (!tbh)
1159                         continue;
1160                 if (unlikely(test_set_buffer_locked(tbh)))
1161                         BUG();
1162                 /* The buffer dirty state is now irrelevant, just clean it. */
1163                 clear_buffer_dirty(tbh);
1164                 BUG_ON(!buffer_uptodate(tbh));
1165                 BUG_ON(!buffer_mapped(tbh));
1166                 get_bh(tbh);
1167                 tbh->b_end_io = end_buffer_write_sync;
1168                 submit_bh(WRITE, tbh);
1169         }
1170         /* Synchronize the mft mirror now if not @sync. */
1171         if (is_mft && !sync)
1172                 goto do_mirror;
1173 do_wait:
1174         /* Wait on i/o completion of buffers. */
1175         for (i = 0; i < nr_bhs; i++) {
1176                 tbh = bhs[i];
1177                 if (!tbh)
1178                         continue;
1179                 wait_on_buffer(tbh);
1180                 if (unlikely(!buffer_uptodate(tbh))) {
1181                         ntfs_error(vol->sb, "I/O error while writing ntfs "
1182                                         "record buffer (inode 0x%lx, "
1183                                         "attribute type 0x%x, page index "
1184                                         "0x%lx, page offset 0x%lx)!  Unmount "
1185                                         "and run chkdsk.", vi->i_ino, ni->type,
1186                                         page->index, bh_offset(tbh));
1187                         if (!err || err == -ENOMEM)
1188                                 err = -EIO;
1189                         /*
1190                          * Set the buffer uptodate so the page and buffer
1191                          * states do not become out of sync.
1192                          */
1193                         set_buffer_uptodate(tbh);
1194                 }
1195         }
1196         /* If @sync, now synchronize the mft mirror. */
1197         if (is_mft && sync) {
1198 do_mirror:
1199                 for (i = 0; i < nr_bhs; i++) {
1200                         unsigned long mft_no;
1201                         unsigned int ofs;
1202
1203                         /*
1204                          * Skip buffers which are not at the beginning of
1205                          * records.
1206                          */
1207                         if (i % bhs_per_rec)
1208                                 continue;
1209                         tbh = bhs[i];
1210                         /* Skip removed buffers (and hence records). */
1211                         if (!tbh)
1212                                 continue;
1213                         ofs = bh_offset(tbh);
1214                         /* Get the mft record number. */
1215                         mft_no = (((s64)page->index << PAGE_CACHE_SHIFT) + ofs)
1216                                         >> rec_size_bits;
1217                         if (mft_no < vol->mftmirr_size)
1218                                 ntfs_sync_mft_mirror(vol, mft_no,
1219                                                 (MFT_RECORD*)(kaddr + ofs),
1220                                                 sync);
1221                 }
1222                 if (!sync)
1223                         goto do_wait;
1224         }
1225         /* Remove the mst protection fixups again. */
1226         for (i = 0; i < nr_bhs; i++) {
1227                 if (!(i % bhs_per_rec)) {
1228                         tbh = bhs[i];
1229                         if (!tbh)
1230                                 continue;
1231                         post_write_mst_fixup((NTFS_RECORD*)(kaddr +
1232                                         bh_offset(tbh)));
1233                 }
1234         }
1235         flush_dcache_page(page);
1236 unm_done:
1237         /* Unlock any locked inodes. */
1238         while (nr_locked_nis-- > 0) {
1239                 ntfs_inode *tni, *base_tni;
1240
1241                 tni = locked_nis[nr_locked_nis];
1242                 /* Get the base inode. */
1243                 down(&tni->extent_lock);
1244                 if (tni->nr_extents >= 0)
1245                         base_tni = tni;
1246                 else {
1247                         base_tni = tni->ext.base_ntfs_ino;
1248                         BUG_ON(!base_tni);
1249                 }
1250                 up(&tni->extent_lock);
1251                 ntfs_debug("Unlocking %s inode 0x%lx.",
1252                                 tni == base_tni ? "base" : "extent",
1253                                 tni->mft_no);
1254                 up(&tni->mrec_lock);
1255                 atomic_dec(&tni->count);
1256                 iput(VFS_I(base_tni));
1257         }
1258         SetPageUptodate(page);
1259         kunmap(page);
1260 done:
1261         if (unlikely(err && err != -ENOMEM)) {
1262                 /*
1263                  * Set page error if there is only one ntfs record in the page.
1264                  * Otherwise we would loose per-record granularity.
1265                  */
1266                 if (ni->itype.index.block_size == PAGE_CACHE_SIZE)
1267                         SetPageError(page);
1268                 NVolSetErrors(vol);
1269         }
1270         if (page_is_dirty) {
1271                 ntfs_debug("Page still contains one or more dirty ntfs "
1272                                 "records.  Redirtying the page starting at "
1273                                 "record 0x%lx.", page->index <<
1274                                 (PAGE_CACHE_SHIFT - rec_size_bits));
1275                 redirty_page_for_writepage(wbc, page);
1276                 unlock_page(page);
1277         } else {
1278                 /*
1279                  * Keep the VM happy.  This must be done otherwise the
1280                  * radix-tree tag PAGECACHE_TAG_DIRTY remains set even though
1281                  * the page is clean.
1282                  */
1283                 BUG_ON(PageWriteback(page));
1284                 set_page_writeback(page);
1285                 unlock_page(page);
1286                 end_page_writeback(page);
1287         }
1288         if (likely(!err))
1289                 ntfs_debug("Done.");
1290         return err;
1291 }
1292
1293 /**
1294  * ntfs_writepage - write a @page to the backing store
1295  * @page:       page cache page to write out
1296  * @wbc:        writeback control structure
1297  *
1298  * This is called from the VM when it wants to have a dirty ntfs page cache
1299  * page cleaned.  The VM has already locked the page and marked it clean.
1300  *
1301  * For non-resident attributes, ntfs_writepage() writes the @page by calling
1302  * the ntfs version of the generic block_write_full_page() function,
1303  * ntfs_write_block(), which in turn if necessary creates and writes the
1304  * buffers associated with the page asynchronously.
1305  *
1306  * For resident attributes, OTOH, ntfs_writepage() writes the @page by copying
1307  * the data to the mft record (which at this stage is most likely in memory).
1308  * The mft record is then marked dirty and written out asynchronously via the
1309  * vfs inode dirty code path for the inode the mft record belongs to or via the
1310  * vm page dirty code path for the page the mft record is in.
1311  *
1312  * Based on ntfs_readpage() and fs/buffer.c::block_write_full_page().
1313  *
1314  * Return 0 on success and -errno on error.
1315  */
1316 static int ntfs_writepage(struct page *page, struct writeback_control *wbc)
1317 {
1318         loff_t i_size;
1319         struct inode *vi = page->mapping->host;
1320         ntfs_inode *base_ni = NULL, *ni = NTFS_I(vi);
1321         char *kaddr;
1322         ntfs_attr_search_ctx *ctx = NULL;
1323         MFT_RECORD *m = NULL;
1324         u32 attr_len;
1325         int err;
1326
1327 retry_writepage:
1328         BUG_ON(!PageLocked(page));
1329         i_size = i_size_read(vi);
1330         /* Is the page fully outside i_size? (truncate in progress) */
1331         if (unlikely(page->index >= (i_size + PAGE_CACHE_SIZE - 1) >>
1332                         PAGE_CACHE_SHIFT)) {
1333                 /*
1334                  * The page may have dirty, unmapped buffers.  Make them
1335                  * freeable here, so the page does not leak.
1336                  */
1337                 block_invalidatepage(page, 0);
1338                 unlock_page(page);
1339                 ntfs_debug("Write outside i_size - truncated?");
1340                 return 0;
1341         }
1342         /*
1343          * Only $DATA attributes can be encrypted and only unnamed $DATA
1344          * attributes can be compressed.  Index root can have the flags set but
1345          * this means to create compressed/encrypted files, not that the
1346          * attribute is compressed/encrypted.  Note we need to check for
1347          * AT_INDEX_ALLOCATION since this is the type of both directory and
1348          * index inodes.
1349          */
1350         if (ni->type != AT_INDEX_ALLOCATION) {
1351                 /* If file is encrypted, deny access, just like NT4. */
1352                 if (NInoEncrypted(ni)) {
1353                         unlock_page(page);
1354                         BUG_ON(ni->type != AT_DATA);
1355                         ntfs_debug("Denying write access to encrypted "
1356                                         "file.");
1357                         return -EACCES;
1358                 }
1359                 /* Compressed data streams are handled in compress.c. */
1360                 if (NInoNonResident(ni) && NInoCompressed(ni)) {
1361                         BUG_ON(ni->type != AT_DATA);
1362                         BUG_ON(ni->name_len);
1363                         // TODO: Implement and replace this with
1364                         // return ntfs_write_compressed_block(page);
1365                         unlock_page(page);
1366                         ntfs_error(vi->i_sb, "Writing to compressed files is "
1367                                         "not supported yet.  Sorry.");
1368                         return -EOPNOTSUPP;
1369                 }
1370                 // TODO: Implement and remove this check.
1371                 if (NInoNonResident(ni) && NInoSparse(ni)) {
1372                         unlock_page(page);
1373                         ntfs_error(vi->i_sb, "Writing to sparse files is not "
1374                                         "supported yet.  Sorry.");
1375                         return -EOPNOTSUPP;
1376                 }
1377         }
1378         /* NInoNonResident() == NInoIndexAllocPresent() */
1379         if (NInoNonResident(ni)) {
1380                 /* We have to zero every time due to mmap-at-end-of-file. */
1381                 if (page->index >= (i_size >> PAGE_CACHE_SHIFT)) {
1382                         /* The page straddles i_size. */
1383                         unsigned int ofs = i_size & ~PAGE_CACHE_MASK;
1384                         kaddr = kmap_atomic(page, KM_USER0);
1385                         memset(kaddr + ofs, 0, PAGE_CACHE_SIZE - ofs);
1386                         flush_dcache_page(page);
1387                         kunmap_atomic(kaddr, KM_USER0);
1388                 }
1389                 /* Handle mst protected attributes. */
1390                 if (NInoMstProtected(ni))
1391                         return ntfs_write_mst_block(page, wbc);
1392                 /* Normal, non-resident data stream. */
1393                 return ntfs_write_block(page, wbc);
1394         }
1395         /*
1396          * Attribute is resident, implying it is not compressed, encrypted, or
1397          * mst protected.  This also means the attribute is smaller than an mft
1398          * record and hence smaller than a page, so can simply return error on
1399          * any pages with index above 0.  Note the attribute can actually be
1400          * marked compressed but if it is resident the actual data is not
1401          * compressed so we are ok to ignore the compressed flag here.
1402          */
1403         BUG_ON(page_has_buffers(page));
1404         BUG_ON(!PageUptodate(page));
1405         if (unlikely(page->index > 0)) {
1406                 ntfs_error(vi->i_sb, "BUG()! page->index (0x%lx) > 0.  "
1407                                 "Aborting write.", page->index);
1408                 BUG_ON(PageWriteback(page));
1409                 set_page_writeback(page);
1410                 unlock_page(page);
1411                 end_page_writeback(page);
1412                 return -EIO;
1413         }
1414         if (!NInoAttr(ni))
1415                 base_ni = ni;
1416         else
1417                 base_ni = ni->ext.base_ntfs_ino;
1418         /* Map, pin, and lock the mft record. */
1419         m = map_mft_record(base_ni);
1420         if (IS_ERR(m)) {
1421                 err = PTR_ERR(m);
1422                 m = NULL;
1423                 ctx = NULL;
1424                 goto err_out;
1425         }
1426         /*
1427          * If a parallel write made the attribute non-resident, drop the mft
1428          * record and retry the writepage.
1429          */
1430         if (unlikely(NInoNonResident(ni))) {
1431                 unmap_mft_record(base_ni);
1432                 goto retry_writepage;
1433         }
1434         ctx = ntfs_attr_get_search_ctx(base_ni, m);
1435         if (unlikely(!ctx)) {
1436                 err = -ENOMEM;
1437                 goto err_out;
1438         }
1439         err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
1440                         CASE_SENSITIVE, 0, NULL, 0, ctx);
1441         if (unlikely(err))
1442                 goto err_out;
1443         /*
1444          * Keep the VM happy.  This must be done otherwise the radix-tree tag
1445          * PAGECACHE_TAG_DIRTY remains set even though the page is clean.
1446          */
1447         BUG_ON(PageWriteback(page));
1448         set_page_writeback(page);
1449         unlock_page(page);
1450         /*
1451          * Here, we do not need to zero the out of bounds area everytime
1452          * because the below memcpy() already takes care of the
1453          * mmap-at-end-of-file requirements.  If the file is converted to a
1454          * non-resident one, then the code path use is switched to the
1455          * non-resident one where the zeroing happens on each ntfs_writepage()
1456          * invocation.
1457          */
1458         attr_len = le32_to_cpu(ctx->attr->data.resident.value_length);
1459         i_size = i_size_read(vi);
1460         if (unlikely(attr_len > i_size)) {
1461                 attr_len = i_size;
1462                 ctx->attr->data.resident.value_length = cpu_to_le32(attr_len);
1463         }
1464         kaddr = kmap_atomic(page, KM_USER0);
1465         /* Copy the data from the page to the mft record. */
1466         memcpy((u8*)ctx->attr +
1467                         le16_to_cpu(ctx->attr->data.resident.value_offset),
1468                         kaddr, attr_len);
1469         flush_dcache_mft_record_page(ctx->ntfs_ino);
1470         /* Zero out of bounds area in the page cache page. */
1471         memset(kaddr + attr_len, 0, PAGE_CACHE_SIZE - attr_len);
1472         flush_dcache_page(page);
1473         kunmap_atomic(kaddr, KM_USER0);
1474
1475         end_page_writeback(page);
1476
1477         /* Mark the mft record dirty, so it gets written back. */
1478         mark_mft_record_dirty(ctx->ntfs_ino);
1479         ntfs_attr_put_search_ctx(ctx);
1480         unmap_mft_record(base_ni);
1481         return 0;
1482 err_out:
1483         if (err == -ENOMEM) {
1484                 ntfs_warning(vi->i_sb, "Error allocating memory. Redirtying "
1485                                 "page so we try again later.");
1486                 /*
1487                  * Put the page back on mapping->dirty_pages, but leave its
1488                  * buffers' dirty state as-is.
1489                  */
1490                 redirty_page_for_writepage(wbc, page);
1491                 err = 0;
1492         } else {
1493                 ntfs_error(vi->i_sb, "Resident attribute write failed with "
1494                                 "error %i.", err);
1495                 SetPageError(page);
1496                 NVolSetErrors(ni->vol);
1497                 make_bad_inode(vi);
1498         }
1499         unlock_page(page);
1500         if (ctx)
1501                 ntfs_attr_put_search_ctx(ctx);
1502         if (m)
1503                 unmap_mft_record(base_ni);
1504         return err;
1505 }
1506
1507 /**
1508  * ntfs_prepare_nonresident_write -
1509  *
1510  */
1511 static int ntfs_prepare_nonresident_write(struct page *page,
1512                 unsigned from, unsigned to)
1513 {
1514         VCN vcn;
1515         LCN lcn;
1516         s64 initialized_size;
1517         loff_t i_size;
1518         sector_t block, ablock, iblock;
1519         struct inode *vi;
1520         ntfs_inode *ni;
1521         ntfs_volume *vol;
1522         runlist_element *rl;
1523         struct buffer_head *bh, *head, *wait[2], **wait_bh = wait;
1524         unsigned long flags;
1525         unsigned int vcn_ofs, block_start, block_end, blocksize;
1526         int err;
1527         BOOL is_retry;
1528         unsigned char blocksize_bits;
1529
1530         vi = page->mapping->host;
1531         ni = NTFS_I(vi);
1532         vol = ni->vol;
1533
1534         ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
1535                         "0x%lx, from = %u, to = %u.", ni->mft_no, ni->type,
1536                         page->index, from, to);
1537
1538         BUG_ON(!NInoNonResident(ni));
1539
1540         blocksize_bits = vi->i_blkbits;
1541         blocksize = 1 << blocksize_bits;
1542
1543         /*
1544          * create_empty_buffers() will create uptodate/dirty buffers if the
1545          * page is uptodate/dirty.
1546          */
1547         if (!page_has_buffers(page))
1548                 create_empty_buffers(page, blocksize, 0);
1549         bh = head = page_buffers(page);
1550         if (unlikely(!bh))
1551                 return -ENOMEM;
1552
1553         /* The first block in the page. */
1554         block = (s64)page->index << (PAGE_CACHE_SHIFT - blocksize_bits);
1555
1556         read_lock_irqsave(&ni->size_lock, flags);
1557         /*
1558          * The first out of bounds block for the allocated size.  No need to
1559          * round up as allocated_size is in multiples of cluster size and the
1560          * minimum cluster size is 512 bytes, which is equal to the smallest
1561          * blocksize.
1562          */
1563         ablock = ni->allocated_size >> blocksize_bits;
1564         i_size = i_size_read(vi);
1565         initialized_size = ni->initialized_size;
1566         read_unlock_irqrestore(&ni->size_lock, flags);
1567
1568         /* The last (fully or partially) initialized block. */
1569         iblock = initialized_size >> blocksize_bits;
1570
1571         /* Loop through all the buffers in the page. */
1572         block_start = 0;
1573         rl = NULL;
1574         err = 0;
1575         do {
1576                 block_end = block_start + blocksize;
1577                 /*
1578                  * If buffer @bh is outside the write, just mark it uptodate
1579                  * if the page is uptodate and continue with the next buffer.
1580                  */
1581                 if (block_end <= from || block_start >= to) {
1582                         if (PageUptodate(page)) {
1583                                 if (!buffer_uptodate(bh))
1584                                         set_buffer_uptodate(bh);
1585                         }
1586                         continue;
1587                 }
1588                 /*
1589                  * @bh is at least partially being written to.
1590                  * Make sure it is not marked as new.
1591                  */
1592                 //if (buffer_new(bh))
1593                 //      clear_buffer_new(bh);
1594
1595                 if (block >= ablock) {
1596                         // TODO: block is above allocated_size, need to
1597                         // allocate it. Best done in one go to accommodate not
1598                         // only block but all above blocks up to and including:
1599                         // ((page->index << PAGE_CACHE_SHIFT) + to + blocksize
1600                         // - 1) >> blobksize_bits. Obviously will need to round
1601                         // up to next cluster boundary, too. This should be
1602                         // done with a helper function, so it can be reused.
1603                         ntfs_error(vol->sb, "Writing beyond allocated size "
1604                                         "is not supported yet. Sorry.");
1605                         err = -EOPNOTSUPP;
1606                         goto err_out;
1607                         // Need to update ablock.
1608                         // Need to set_buffer_new() on all block bhs that are
1609                         // newly allocated.
1610                 }
1611                 /*
1612                  * Now we have enough allocated size to fulfill the whole
1613                  * request, i.e. block < ablock is true.
1614                  */
1615                 if (unlikely((block >= iblock) &&
1616                                 (initialized_size < i_size))) {
1617                         /*
1618                          * If this page is fully outside initialized size, zero
1619                          * out all pages between the current initialized size
1620                          * and the current page. Just use ntfs_readpage() to do
1621                          * the zeroing transparently.
1622                          */
1623                         if (block > iblock) {
1624                                 // TODO:
1625                                 // For each page do:
1626                                 // - read_cache_page()
1627                                 // Again for each page do:
1628                                 // - wait_on_page_locked()
1629                                 // - Check (PageUptodate(page) &&
1630                                 //                      !PageError(page))
1631                                 // Update initialized size in the attribute and
1632                                 // in the inode.
1633                                 // Again, for each page do:
1634                                 //      __set_page_dirty_buffers();
1635                                 // page_cache_release()
1636                                 // We don't need to wait on the writes.
1637                                 // Update iblock.
1638                         }
1639                         /*
1640                          * The current page straddles initialized size. Zero
1641                          * all non-uptodate buffers and set them uptodate (and
1642                          * dirty?). Note, there aren't any non-uptodate buffers
1643                          * if the page is uptodate.
1644                          * FIXME: For an uptodate page, the buffers may need to
1645                          * be written out because they were not initialized on
1646                          * disk before.
1647                          */
1648                         if (!PageUptodate(page)) {
1649                                 // TODO:
1650                                 // Zero any non-uptodate buffers up to i_size.
1651                                 // Set them uptodate and dirty.
1652                         }
1653                         // TODO:
1654                         // Update initialized size in the attribute and in the
1655                         // inode (up to i_size).
1656                         // Update iblock.
1657                         // FIXME: This is inefficient. Try to batch the two
1658                         // size changes to happen in one go.
1659                         ntfs_error(vol->sb, "Writing beyond initialized size "
1660                                         "is not supported yet. Sorry.");
1661                         err = -EOPNOTSUPP;
1662                         goto err_out;
1663                         // Do NOT set_buffer_new() BUT DO clear buffer range
1664                         // outside write request range.
1665                         // set_buffer_uptodate() on complete buffers as well as
1666                         // set_buffer_dirty().
1667                 }
1668
1669                 /* Need to map unmapped buffers. */
1670                 if (!buffer_mapped(bh)) {
1671                         /* Unmapped buffer. Need to map it. */
1672                         bh->b_bdev = vol->sb->s_bdev;
1673
1674                         /* Convert block into corresponding vcn and offset. */
1675                         vcn = (VCN)block << blocksize_bits >>
1676                                         vol->cluster_size_bits;
1677                         vcn_ofs = ((VCN)block << blocksize_bits) &
1678                                         vol->cluster_size_mask;
1679
1680                         is_retry = FALSE;
1681                         if (!rl) {
1682 lock_retry_remap:
1683                                 down_read(&ni->runlist.lock);
1684                                 rl = ni->runlist.rl;
1685                         }
1686                         if (likely(rl != NULL)) {
1687                                 /* Seek to element containing target vcn. */
1688                                 while (rl->length && rl[1].vcn <= vcn)
1689                                         rl++;
1690                                 lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
1691                         } else
1692                                 lcn = LCN_RL_NOT_MAPPED;
1693                         if (unlikely(lcn < 0)) {
1694                                 /*
1695                                  * We extended the attribute allocation above.
1696                                  * If we hit an ENOENT here it means that the
1697                                  * allocation was insufficient which is a bug.
1698                                  */
1699                                 BUG_ON(lcn == LCN_ENOENT);
1700
1701                                 /* It is a hole, need to instantiate it. */
1702                                 if (lcn == LCN_HOLE) {
1703                                         // TODO: Instantiate the hole.
1704                                         // clear_buffer_new(bh);
1705                                         // unmap_underlying_metadata(bh->b_bdev,
1706                                         //              bh->b_blocknr);
1707                                         // For non-uptodate buffers, need to
1708                                         // zero out the region outside the
1709                                         // request in this bh or all bhs,
1710                                         // depending on what we implemented
1711                                         // above.
1712                                         // Need to flush_dcache_page().
1713                                         // Or could use set_buffer_new()
1714                                         // instead?
1715                                         ntfs_error(vol->sb, "Writing into "
1716                                                         "sparse regions is "
1717                                                         "not supported yet. "
1718                                                         "Sorry.");
1719                                         err = -EOPNOTSUPP;
1720                                         if (!rl)
1721                                                 up_read(&ni->runlist.lock);
1722                                         goto err_out;
1723                                 } else if (!is_retry &&
1724                                                 lcn == LCN_RL_NOT_MAPPED) {
1725                                         is_retry = TRUE;
1726                                         /*
1727                                          * Attempt to map runlist, dropping
1728                                          * lock for the duration.
1729                                          */
1730                                         up_read(&ni->runlist.lock);
1731                                         err = ntfs_map_runlist(ni, vcn);
1732                                         if (likely(!err))
1733                                                 goto lock_retry_remap;
1734                                         rl = NULL;
1735                                 } else if (!rl)
1736                                         up_read(&ni->runlist.lock);
1737                                 /*
1738                                  * Failed to map the buffer, even after
1739                                  * retrying.
1740                                  */
1741                                 if (!err)
1742                                         err = -EIO;
1743                                 bh->b_blocknr = -1;
1744                                 ntfs_error(vol->sb, "Failed to write to inode "
1745                                                 "0x%lx, attribute type 0x%x, "
1746                                                 "vcn 0x%llx, offset 0x%x "
1747                                                 "because its location on disk "
1748                                                 "could not be determined%s "
1749                                                 "(error code %i).",
1750                                                 ni->mft_no, ni->type,
1751                                                 (unsigned long long)vcn,
1752                                                 vcn_ofs, is_retry ? " even "
1753                                                 "after retrying" : "", err);
1754                                 goto err_out;
1755                         }
1756                         /* We now have a successful remap, i.e. lcn >= 0. */
1757
1758                         /* Setup buffer head to correct block. */
1759                         bh->b_blocknr = ((lcn << vol->cluster_size_bits)
1760                                         + vcn_ofs) >> blocksize_bits;
1761                         set_buffer_mapped(bh);
1762
1763                         // FIXME: Something analogous to this is needed for
1764                         // each newly allocated block, i.e. BH_New.
1765                         // FIXME: Might need to take this out of the
1766                         // if (!buffer_mapped(bh)) {}, depending on how we
1767                         // implement things during the allocated_size and
1768                         // initialized_size extension code above.
1769                         if (buffer_new(bh)) {
1770                                 clear_buffer_new(bh);
1771                                 unmap_underlying_metadata(bh->b_bdev,
1772                                                 bh->b_blocknr);
1773                                 if (PageUptodate(page)) {
1774                                         set_buffer_uptodate(bh);
1775                                         continue;
1776                                 }
1777                                 /*
1778                                  * Page is _not_ uptodate, zero surrounding
1779                                  * region. NOTE: This is how we decide if to
1780                                  * zero or not!
1781                                  */
1782                                 if (block_end > to || block_start < from) {
1783                                         void *kaddr;
1784
1785                                         kaddr = kmap_atomic(page, KM_USER0);
1786                                         if (block_end > to)
1787                                                 memset(kaddr + to, 0,
1788                                                                 block_end - to);
1789                                         if (block_start < from)
1790                                                 memset(kaddr + block_start, 0,
1791                                                                 from -
1792                                                                 block_start);
1793                                         flush_dcache_page(page);
1794                                         kunmap_atomic(kaddr, KM_USER0);
1795                                 }
1796                                 continue;
1797                         }
1798                 }
1799                 /* @bh is mapped, set it uptodate if the page is uptodate. */
1800                 if (PageUptodate(page)) {
1801                         if (!buffer_uptodate(bh))
1802                                 set_buffer_uptodate(bh);
1803                         continue;
1804                 }
1805                 /*
1806                  * The page is not uptodate. The buffer is mapped. If it is not
1807                  * uptodate, and it is only partially being written to, we need
1808                  * to read the buffer in before the write, i.e. right now.
1809                  */
1810                 if (!buffer_uptodate(bh) &&
1811                                 (block_start < from || block_end > to)) {
1812                         ll_rw_block(READ, 1, &bh);
1813                         *wait_bh++ = bh;
1814                 }
1815         } while (block++, block_start = block_end,
1816                         (bh = bh->b_this_page) != head);
1817
1818         /* Release the lock if we took it. */
1819         if (rl) {
1820                 up_read(&ni->runlist.lock);
1821                 rl = NULL;
1822         }
1823
1824         /* If we issued read requests, let them complete. */
1825         while (wait_bh > wait) {
1826                 wait_on_buffer(*--wait_bh);
1827                 if (!buffer_uptodate(*wait_bh))
1828                         return -EIO;
1829         }
1830
1831         ntfs_debug("Done.");
1832         return 0;
1833 err_out:
1834         /*
1835          * Zero out any newly allocated blocks to avoid exposing stale data.
1836          * If BH_New is set, we know that the block was newly allocated in the
1837          * above loop.
1838          * FIXME: What about initialized_size increments? Have we done all the
1839          * required zeroing above? If not this error handling is broken, and
1840          * in particular the if (block_end <= from) check is completely bogus.
1841          */
1842         bh = head;
1843         block_start = 0;
1844         is_retry = FALSE;
1845         do {
1846                 block_end = block_start + blocksize;
1847                 if (block_end <= from)
1848                         continue;
1849                 if (block_start >= to)
1850                         break;
1851                 if (buffer_new(bh)) {
1852                         void *kaddr;
1853
1854                         clear_buffer_new(bh);
1855                         kaddr = kmap_atomic(page, KM_USER0);
1856                         memset(kaddr + block_start, 0, bh->b_size);
1857                         kunmap_atomic(kaddr, KM_USER0);
1858                         set_buffer_uptodate(bh);
1859                         mark_buffer_dirty(bh);
1860                         is_retry = TRUE;
1861                 }
1862         } while (block_start = block_end, (bh = bh->b_this_page) != head);
1863         if (is_retry)
1864                 flush_dcache_page(page);
1865         if (rl)
1866                 up_read(&ni->runlist.lock);
1867         return err;
1868 }
1869
1870 /**
1871  * ntfs_prepare_write - prepare a page for receiving data
1872  *
1873  * This is called from generic_file_write() with i_sem held on the inode
1874  * (@page->mapping->host).  The @page is locked but not kmap()ped.  The source
1875  * data has not yet been copied into the @page.
1876  *
1877  * Need to extend the attribute/fill in holes if necessary, create blocks and
1878  * make partially overwritten blocks uptodate,
1879  *
1880  * i_size is not to be modified yet.
1881  *
1882  * Return 0 on success or -errno on error.
1883  *
1884  * Should be using block_prepare_write() [support for sparse files] or
1885  * cont_prepare_write() [no support for sparse files].  Cannot do that due to
1886  * ntfs specifics but can look at them for implementation guidance.
1887  *
1888  * Note: In the range, @from is inclusive and @to is exclusive, i.e. @from is
1889  * the first byte in the page that will be written to and @to is the first byte
1890  * after the last byte that will be written to.
1891  */
1892 static int ntfs_prepare_write(struct file *file, struct page *page,
1893                 unsigned from, unsigned to)
1894 {
1895         s64 new_size;
1896         loff_t i_size;
1897         struct inode *vi = page->mapping->host;
1898         ntfs_inode *base_ni = NULL, *ni = NTFS_I(vi);
1899         ntfs_volume *vol = ni->vol;
1900         ntfs_attr_search_ctx *ctx = NULL;
1901         MFT_RECORD *m = NULL;
1902         ATTR_RECORD *a;
1903         u8 *kaddr;
1904         u32 attr_len;
1905         int err;
1906
1907         ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
1908                         "0x%lx, from = %u, to = %u.", vi->i_ino, ni->type,
1909                         page->index, from, to);
1910         BUG_ON(!PageLocked(page));
1911         BUG_ON(from > PAGE_CACHE_SIZE);
1912         BUG_ON(to > PAGE_CACHE_SIZE);
1913         BUG_ON(from > to);
1914         BUG_ON(NInoMstProtected(ni));
1915         /*
1916          * If a previous ntfs_truncate() failed, repeat it and abort if it
1917          * fails again.
1918          */
1919         if (unlikely(NInoTruncateFailed(ni))) {
1920                 down_write(&vi->i_alloc_sem);
1921                 err = ntfs_truncate(vi);
1922                 up_write(&vi->i_alloc_sem);
1923                 if (err || NInoTruncateFailed(ni)) {
1924                         if (!err)
1925                                 err = -EIO;
1926                         goto err_out;
1927                 }
1928         }
1929         /* If the attribute is not resident, deal with it elsewhere. */
1930         if (NInoNonResident(ni)) {
1931                 /*
1932                  * Only unnamed $DATA attributes can be compressed, encrypted,
1933                  * and/or sparse.
1934                  */
1935                 if (ni->type == AT_DATA && !ni->name_len) {
1936                         /* If file is encrypted, deny access, just like NT4. */
1937                         if (NInoEncrypted(ni)) {
1938                                 ntfs_debug("Denying write access to encrypted "
1939                                                 "file.");
1940                                 return -EACCES;
1941                         }
1942                         /* Compressed data streams are handled in compress.c. */
1943                         if (NInoCompressed(ni)) {
1944                                 // TODO: Implement and replace this check with
1945                                 // return ntfs_write_compressed_block(page);
1946                                 ntfs_error(vi->i_sb, "Writing to compressed "
1947                                                 "files is not supported yet. "
1948                                                 "Sorry.");
1949                                 return -EOPNOTSUPP;
1950                         }
1951                         // TODO: Implement and remove this check.
1952                         if (NInoSparse(ni)) {
1953                                 ntfs_error(vi->i_sb, "Writing to sparse files "
1954                                                 "is not supported yet. Sorry.");
1955                                 return -EOPNOTSUPP;
1956                         }
1957                 }
1958                 /* Normal data stream. */
1959                 return ntfs_prepare_nonresident_write(page, from, to);
1960         }
1961         /*
1962          * Attribute is resident, implying it is not compressed, encrypted, or
1963          * sparse.
1964          */
1965         BUG_ON(page_has_buffers(page));
1966         new_size = ((s64)page->index << PAGE_CACHE_SHIFT) + to;
1967         /* If we do not need to resize the attribute allocation we are done. */
1968         if (new_size <= i_size_read(vi))
1969                 goto done;
1970         /* Map, pin, and lock the (base) mft record. */
1971         if (!NInoAttr(ni))
1972                 base_ni = ni;
1973         else
1974                 base_ni = ni->ext.base_ntfs_ino;
1975         m = map_mft_record(base_ni);
1976         if (IS_ERR(m)) {
1977                 err = PTR_ERR(m);
1978                 m = NULL;
1979                 ctx = NULL;
1980                 goto err_out;
1981         }
1982         ctx = ntfs_attr_get_search_ctx(base_ni, m);
1983         if (unlikely(!ctx)) {
1984                 err = -ENOMEM;
1985                 goto err_out;
1986         }
1987         err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
1988                         CASE_SENSITIVE, 0, NULL, 0, ctx);
1989         if (unlikely(err)) {
1990                 if (err == -ENOENT)
1991                         err = -EIO;
1992                 goto err_out;
1993         }
1994         m = ctx->mrec;
1995         a = ctx->attr;
1996         /* The total length of the attribute value. */
1997         attr_len = le32_to_cpu(a->data.resident.value_length);
1998         /* Fix an eventual previous failure of ntfs_commit_write(). */
1999         i_size = i_size_read(vi);
2000         if (unlikely(attr_len > i_size)) {
2001                 attr_len = i_size;
2002                 a->data.resident.value_length = cpu_to_le32(attr_len);
2003         }
2004         /* If we do not need to resize the attribute allocation we are done. */
2005         if (new_size <= attr_len)
2006                 goto done_unm;
2007         /* Check if new size is allowed in $AttrDef. */
2008         err = ntfs_attr_size_bounds_check(vol, ni->type, new_size);
2009         if (unlikely(err)) {
2010                 if (err == -ERANGE) {
2011                         ntfs_error(vol->sb, "Write would cause the inode "
2012                                         "0x%lx to exceed the maximum size for "
2013                                         "its attribute type (0x%x).  Aborting "
2014                                         "write.", vi->i_ino,
2015                                         le32_to_cpu(ni->type));
2016                 } else {
2017                         ntfs_error(vol->sb, "Inode 0x%lx has unknown "
2018                                         "attribute type 0x%x.  Aborting "
2019                                         "write.", vi->i_ino,
2020                                         le32_to_cpu(ni->type));
2021                         err = -EIO;
2022                 }
2023                 goto err_out2;
2024         }
2025         /*
2026          * Extend the attribute record to be able to store the new attribute
2027          * size.
2028          */
2029         if (new_size >= vol->mft_record_size || ntfs_attr_record_resize(m, a,
2030                         le16_to_cpu(a->data.resident.value_offset) +
2031                         new_size)) {
2032                 /* Not enough space in the mft record. */
2033                 ntfs_error(vol->sb, "Not enough space in the mft record for "
2034                                 "the resized attribute value.  This is not "
2035                                 "supported yet.  Aborting write.");
2036                 err = -EOPNOTSUPP;
2037                 goto err_out2;
2038         }
2039         /*
2040          * We have enough space in the mft record to fit the write.  This
2041          * implies the attribute is smaller than the mft record and hence the
2042          * attribute must be in a single page and hence page->index must be 0.
2043          */
2044         BUG_ON(page->index);
2045         /*
2046          * If the beginning of the write is past the old size, enlarge the
2047          * attribute value up to the beginning of the write and fill it with
2048          * zeroes.
2049          */
2050         if (from > attr_len) {
2051                 memset((u8*)a + le16_to_cpu(a->data.resident.value_offset) +
2052                                 attr_len, 0, from - attr_len);
2053                 a->data.resident.value_length = cpu_to_le32(from);
2054                 /* Zero the corresponding area in the page as well. */
2055                 if (PageUptodate(page)) {
2056                         kaddr = kmap_atomic(page, KM_USER0);
2057                         memset(kaddr + attr_len, 0, from - attr_len);
2058                         kunmap_atomic(kaddr, KM_USER0);
2059                         flush_dcache_page(page);
2060                 }
2061         }
2062         flush_dcache_mft_record_page(ctx->ntfs_ino);
2063         mark_mft_record_dirty(ctx->ntfs_ino);
2064 done_unm:
2065         ntfs_attr_put_search_ctx(ctx);
2066         unmap_mft_record(base_ni);
2067         /*
2068          * Because resident attributes are handled by memcpy() to/from the
2069          * corresponding MFT record, and because this form of i/o is byte
2070          * aligned rather than block aligned, there is no need to bring the
2071          * page uptodate here as in the non-resident case where we need to
2072          * bring the buffers straddled by the write uptodate before
2073          * generic_file_write() does the copying from userspace.
2074          *
2075          * We thus defer the uptodate bringing of the page region outside the
2076          * region written to to ntfs_commit_write(), which makes the code
2077          * simpler and saves one atomic kmap which is good.
2078          */
2079 done:
2080         ntfs_debug("Done.");
2081         return 0;
2082 err_out:
2083         if (err == -ENOMEM)
2084                 ntfs_warning(vi->i_sb, "Error allocating memory required to "
2085                                 "prepare the write.");
2086         else {
2087                 ntfs_error(vi->i_sb, "Resident attribute prepare write failed "
2088                                 "with error %i.", err);
2089                 NVolSetErrors(vol);
2090                 make_bad_inode(vi);
2091         }
2092 err_out2:
2093         if (ctx)
2094                 ntfs_attr_put_search_ctx(ctx);
2095         if (m)
2096                 unmap_mft_record(base_ni);
2097         return err;
2098 }
2099
2100 /**
2101  * ntfs_commit_nonresident_write -
2102  *
2103  */
2104 static int ntfs_commit_nonresident_write(struct page *page,
2105                 unsigned from, unsigned to)
2106 {
2107         s64 pos = ((s64)page->index << PAGE_CACHE_SHIFT) + to;
2108         struct inode *vi = page->mapping->host;
2109         struct buffer_head *bh, *head;
2110         unsigned int block_start, block_end, blocksize;
2111         BOOL partial;
2112
2113         ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
2114                         "0x%lx, from = %u, to = %u.", vi->i_ino,
2115                         NTFS_I(vi)->type, page->index, from, to);
2116         blocksize = 1 << vi->i_blkbits;
2117
2118         // FIXME: We need a whole slew of special cases in here for compressed
2119         // files for example...
2120         // For now, we know ntfs_prepare_write() would have failed so we can't
2121         // get here in any of the cases which we have to special case, so we
2122         // are just a ripped off, unrolled generic_commit_write().
2123
2124         bh = head = page_buffers(page);
2125         block_start = 0;
2126         partial = FALSE;
2127         do {
2128                 block_end = block_start + blocksize;
2129                 if (block_end <= from || block_start >= to) {
2130                         if (!buffer_uptodate(bh))
2131                                 partial = TRUE;
2132                 } else {
2133                         set_buffer_uptodate(bh);
2134                         mark_buffer_dirty(bh);
2135                 }
2136         } while (block_start = block_end, (bh = bh->b_this_page) != head);
2137         /*
2138          * If this is a partial write which happened to make all buffers
2139          * uptodate then we can optimize away a bogus ->readpage() for the next
2140          * read().  Here we 'discover' whether the page went uptodate as a
2141          * result of this (potentially partial) write.
2142          */
2143         if (!partial)
2144                 SetPageUptodate(page);
2145         /*
2146          * Not convinced about this at all.  See disparity comment above.  For
2147          * now we know ntfs_prepare_write() would have failed in the write
2148          * exceeds i_size case, so this will never trigger which is fine.
2149          */
2150         if (pos > i_size_read(vi)) {
2151                 ntfs_error(vi->i_sb, "Writing beyond the existing file size is "
2152                                 "not supported yet.  Sorry.");
2153                 return -EOPNOTSUPP;
2154                 // vi->i_size = pos;
2155                 // mark_inode_dirty(vi);
2156         }
2157         ntfs_debug("Done.");
2158         return 0;
2159 }
2160
2161 /**
2162  * ntfs_commit_write - commit the received data
2163  *
2164  * This is called from generic_file_write() with i_sem held on the inode
2165  * (@page->mapping->host).  The @page is locked but not kmap()ped.  The source
2166  * data has already been copied into the @page.  ntfs_prepare_write() has been
2167  * called before the data copied and it returned success so we can take the
2168  * results of various BUG checks and some error handling for granted.
2169  *
2170  * Need to mark modified blocks dirty so they get written out later when
2171  * ntfs_writepage() is invoked by the VM.
2172  *
2173  * Return 0 on success or -errno on error.
2174  *
2175  * Should be using generic_commit_write().  This marks buffers uptodate and
2176  * dirty, sets the page uptodate if all buffers in the page are uptodate, and
2177  * updates i_size if the end of io is beyond i_size.  In that case, it also
2178  * marks the inode dirty.
2179  *
2180  * Cannot use generic_commit_write() due to ntfs specialities but can look at
2181  * it for implementation guidance.
2182  *
2183  * If things have gone as outlined in ntfs_prepare_write(), then we do not
2184  * need to do any page content modifications here at all, except in the write
2185  * to resident attribute case, where we need to do the uptodate bringing here
2186  * which we combine with the copying into the mft record which means we save
2187  * one atomic kmap.
2188  */
2189 static int ntfs_commit_write(struct file *file, struct page *page,
2190                 unsigned from, unsigned to)
2191 {
2192         struct inode *vi = page->mapping->host;
2193         ntfs_inode *base_ni, *ni = NTFS_I(vi);
2194         char *kaddr, *kattr;
2195         ntfs_attr_search_ctx *ctx;
2196         MFT_RECORD *m;
2197         ATTR_RECORD *a;
2198         u32 attr_len;
2199         int err;
2200
2201         ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
2202                         "0x%lx, from = %u, to = %u.", vi->i_ino, ni->type,
2203                         page->index, from, to);
2204         /* If the attribute is not resident, deal with it elsewhere. */
2205         if (NInoNonResident(ni)) {
2206                 /* Only unnamed $DATA attributes can be compressed/encrypted. */
2207                 if (ni->type == AT_DATA && !ni->name_len) {
2208                         /* Encrypted files need separate handling. */
2209                         if (NInoEncrypted(ni)) {
2210                                 // We never get here at present!
2211                                 BUG();
2212                         }
2213                         /* Compressed data streams are handled in compress.c. */
2214                         if (NInoCompressed(ni)) {
2215                                 // TODO: Implement this!
2216                                 // return ntfs_write_compressed_block(page);
2217                                 // We never get here at present!
2218                                 BUG();
2219                         }
2220                 }
2221                 /* Normal data stream. */
2222                 return ntfs_commit_nonresident_write(page, from, to);
2223         }
2224         /*
2225          * Attribute is resident, implying it is not compressed, encrypted, or
2226          * sparse.
2227          */
2228         if (!NInoAttr(ni))
2229                 base_ni = ni;
2230         else
2231                 base_ni = ni->ext.base_ntfs_ino;
2232         /* Map, pin, and lock the mft record. */
2233         m = map_mft_record(base_ni);
2234         if (IS_ERR(m)) {
2235                 err = PTR_ERR(m);
2236                 m = NULL;
2237                 ctx = NULL;
2238                 goto err_out;
2239         }
2240         ctx = ntfs_attr_get_search_ctx(base_ni, m);
2241         if (unlikely(!ctx)) {
2242                 err = -ENOMEM;
2243                 goto err_out;
2244         }
2245         err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
2246                         CASE_SENSITIVE, 0, NULL, 0, ctx);
2247         if (unlikely(err)) {
2248                 if (err == -ENOENT)
2249                         err = -EIO;
2250                 goto err_out;
2251         }
2252         a = ctx->attr;
2253         /* The total length of the attribute value. */
2254         attr_len = le32_to_cpu(a->data.resident.value_length);
2255         BUG_ON(from > attr_len);
2256         kattr = (u8*)a + le16_to_cpu(a->data.resident.value_offset);
2257         kaddr = kmap_atomic(page, KM_USER0);
2258         /* Copy the received data from the page to the mft record. */
2259         memcpy(kattr + from, kaddr + from, to - from);
2260         /* Update the attribute length if necessary. */
2261         if (to > attr_len) {
2262                 attr_len = to;
2263                 a->data.resident.value_length = cpu_to_le32(attr_len);
2264         }
2265         /*
2266          * If the page is not uptodate, bring the out of bounds area(s)
2267          * uptodate by copying data from the mft record to the page.
2268          */
2269         if (!PageUptodate(page)) {
2270                 if (from > 0)
2271                         memcpy(kaddr, kattr, from);
2272                 if (to < attr_len)
2273                         memcpy(kaddr + to, kattr + to, attr_len - to);
2274                 /* Zero the region outside the end of the attribute value. */
2275                 if (attr_len < PAGE_CACHE_SIZE)
2276                         memset(kaddr + attr_len, 0, PAGE_CACHE_SIZE - attr_len);
2277                 /*
2278                  * The probability of not having done any of the above is
2279                  * extremely small, so we just flush unconditionally.
2280                  */
2281                 flush_dcache_page(page);
2282                 SetPageUptodate(page);
2283         }
2284         kunmap_atomic(kaddr, KM_USER0);
2285         /* Update i_size if necessary. */
2286         if (i_size_read(vi) < attr_len) {
2287                 unsigned long flags;
2288
2289                 write_lock_irqsave(&ni->size_lock, flags);
2290                 ni->allocated_size = ni->initialized_size = attr_len;
2291                 i_size_write(vi, attr_len);
2292                 write_unlock_irqrestore(&ni->size_lock, flags);
2293         }
2294         /* Mark the mft record dirty, so it gets written back. */
2295         flush_dcache_mft_record_page(ctx->ntfs_ino);
2296         mark_mft_record_dirty(ctx->ntfs_ino);
2297         ntfs_attr_put_search_ctx(ctx);
2298         unmap_mft_record(base_ni);
2299         ntfs_debug("Done.");
2300         return 0;
2301 err_out:
2302         if (err == -ENOMEM) {
2303                 ntfs_warning(vi->i_sb, "Error allocating memory required to "
2304                                 "commit the write.");
2305                 if (PageUptodate(page)) {
2306                         ntfs_warning(vi->i_sb, "Page is uptodate, setting "
2307                                         "dirty so the write will be retried "
2308                                         "later on by the VM.");
2309                         /*
2310                          * Put the page on mapping->dirty_pages, but leave its
2311                          * buffers' dirty state as-is.
2312                          */
2313                         __set_page_dirty_nobuffers(page);
2314                         err = 0;
2315                 } else
2316                         ntfs_error(vi->i_sb, "Page is not uptodate.  Written "
2317                                         "data has been lost.");
2318         } else {
2319                 ntfs_error(vi->i_sb, "Resident attribute commit write failed "
2320                                 "with error %i.", err);
2321                 NVolSetErrors(ni->vol);
2322                 make_bad_inode(vi);
2323         }
2324         if (ctx)
2325                 ntfs_attr_put_search_ctx(ctx);
2326         if (m)
2327                 unmap_mft_record(base_ni);
2328         return err;
2329 }
2330
2331 #endif  /* NTFS_RW */
2332
2333 /**
2334  * ntfs_aops - general address space operations for inodes and attributes
2335  */
2336 struct address_space_operations ntfs_aops = {
2337         .readpage       = ntfs_readpage,        /* Fill page with data. */
2338         .sync_page      = block_sync_page,      /* Currently, just unplugs the
2339                                                    disk request queue. */
2340 #ifdef NTFS_RW
2341         .writepage      = ntfs_writepage,       /* Write dirty page to disk. */
2342         .prepare_write  = ntfs_prepare_write,   /* Prepare page and buffers
2343                                                    ready to receive data. */
2344         .commit_write   = ntfs_commit_write,    /* Commit received data. */
2345 #endif /* NTFS_RW */
2346 };
2347
2348 /**
2349  * ntfs_mst_aops - general address space operations for mst protecteed inodes
2350  *                 and attributes
2351  */
2352 struct address_space_operations ntfs_mst_aops = {
2353         .readpage       = ntfs_readpage,        /* Fill page with data. */
2354         .sync_page      = block_sync_page,      /* Currently, just unplugs the
2355                                                    disk request queue. */
2356 #ifdef NTFS_RW
2357         .writepage      = ntfs_writepage,       /* Write dirty page to disk. */
2358         .set_page_dirty = __set_page_dirty_nobuffers,   /* Set the page dirty
2359                                                    without touching the buffers
2360                                                    belonging to the page. */
2361 #endif /* NTFS_RW */
2362 };
2363
2364 #ifdef NTFS_RW
2365
2366 /**
2367  * mark_ntfs_record_dirty - mark an ntfs record dirty
2368  * @page:       page containing the ntfs record to mark dirty
2369  * @ofs:        byte offset within @page at which the ntfs record begins
2370  *
2371  * Set the buffers and the page in which the ntfs record is located dirty.
2372  *
2373  * The latter also marks the vfs inode the ntfs record belongs to dirty
2374  * (I_DIRTY_PAGES only).
2375  *
2376  * If the page does not have buffers, we create them and set them uptodate.
2377  * The page may not be locked which is why we need to handle the buffers under
2378  * the mapping->private_lock.  Once the buffers are marked dirty we no longer
2379  * need the lock since try_to_free_buffers() does not free dirty buffers.
2380  */
2381 void mark_ntfs_record_dirty(struct page *page, const unsigned int ofs) {
2382         struct address_space *mapping = page->mapping;
2383         ntfs_inode *ni = NTFS_I(mapping->host);
2384         struct buffer_head *bh, *head, *buffers_to_free = NULL;
2385         unsigned int end, bh_size, bh_ofs;
2386
2387         BUG_ON(!PageUptodate(page));
2388         end = ofs + ni->itype.index.block_size;
2389         bh_size = 1 << VFS_I(ni)->i_blkbits;
2390         spin_lock(&mapping->private_lock);
2391         if (unlikely(!page_has_buffers(page))) {
2392                 spin_unlock(&mapping->private_lock);
2393                 bh = head = alloc_page_buffers(page, bh_size, 1);
2394                 spin_lock(&mapping->private_lock);
2395                 if (likely(!page_has_buffers(page))) {
2396                         struct buffer_head *tail;
2397
2398                         do {
2399                                 set_buffer_uptodate(bh);
2400                                 tail = bh;
2401                                 bh = bh->b_this_page;
2402                         } while (bh);
2403                         tail->b_this_page = head;
2404                         attach_page_buffers(page, head);
2405                 } else
2406                         buffers_to_free = bh;
2407         }
2408         bh = head = page_buffers(page);
2409         BUG_ON(!bh);
2410         do {
2411                 bh_ofs = bh_offset(bh);
2412                 if (bh_ofs + bh_size <= ofs)
2413                         continue;
2414                 if (unlikely(bh_ofs >= end))
2415                         break;
2416                 set_buffer_dirty(bh);
2417         } while ((bh = bh->b_this_page) != head);
2418         spin_unlock(&mapping->private_lock);
2419         __set_page_dirty_nobuffers(page);
2420         if (unlikely(buffers_to_free)) {
2421                 do {
2422                         bh = buffers_to_free->b_this_page;
2423                         free_buffer_head(buffers_to_free);
2424                         buffers_to_free = bh;
2425                 } while (buffers_to_free);
2426         }
2427 }
2428
2429 #endif /* NTFS_RW */