release/src-rt-6.x.4708/linux/linux-2.6.36/fs/ntfs/compress.c

   1 /**
   2  * compress.c - NTFS kernel compressed attributes handling.
   3  *              Part of the Linux-NTFS project.
   4  *
   5  * Copyright (c) 2001-2004 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/fs.h>
  25 #include <linux/buffer_head.h>
  26 #include <linux/blkdev.h>
  27 #include <linux/vmalloc.h>
  28 #include <linux/slab.h>
  29
  30 #include "attrib.h"
  31 #include "inode.h"
  32 #include "debug.h"
  33 #include "ntfs.h"
  34
  35 /**
  36  * ntfs_compression_constants - enum of constants used in the compression code
  37  */
  38 typedef enum {
  39         /* Token types and access mask. */
  40         NTFS_SYMBOL_TOKEN       =       0,
  41         NTFS_PHRASE_TOKEN       =       1,
  42         NTFS_TOKEN_MASK         =       1,
  43
  44         /* Compression sub-block constants. */
  45         NTFS_SB_SIZE_MASK       =       0x0fff,
  46         NTFS_SB_SIZE            =       0x1000,
  47         NTFS_SB_IS_COMPRESSED   =       0x8000,
  48
  49         /*
  50          * The maximum compression block size is by definition 16 * the cluster
  51          * size, with the maximum supported cluster size being 4kiB. Thus the
  52          * maximum compression buffer size is 64kiB, so we use this when
  53          * initializing the compression buffer.
  54          */
  55         NTFS_MAX_CB_SIZE        = 64 * 1024,
  56 } ntfs_compression_constants;
  57
  58 /**
  59  * ntfs_compression_buffer - one buffer for the decompression engine
  60  */
  61 static u8 *ntfs_compression_buffer = NULL;
  62
  63 /**
  64  * ntfs_cb_lock - spinlock which protects ntfs_compression_buffer
  65  */
  66 static DEFINE_SPINLOCK(ntfs_cb_lock);
  67
  68 /**
  69  * allocate_compression_buffers - allocate the decompression buffers
  70  *
  71  * Caller has to hold the ntfs_lock mutex.
  72  *
  73  * Return 0 on success or -ENOMEM if the allocations failed.
  74  */
  75 int allocate_compression_buffers(void)
  76 {
  77         BUG_ON(ntfs_compression_buffer);
  78
  79         ntfs_compression_buffer = vmalloc(NTFS_MAX_CB_SIZE);
  80         if (!ntfs_compression_buffer)
  81                 return -ENOMEM;
  82         return 0;
  83 }
  84
  85 /**
  86  * free_compression_buffers - free the decompression buffers
  87  *
  88  * Caller has to hold the ntfs_lock mutex.
  89  */
  90 void free_compression_buffers(void)
  91 {
  92         BUG_ON(!ntfs_compression_buffer);
  93         vfree(ntfs_compression_buffer);
  94         ntfs_compression_buffer = NULL;
  95 }
  96
  97 /**
  98  * zero_partial_compressed_page - zero out of bounds compressed page region
  99  */
 100 static void zero_partial_compressed_page(struct page *page,
 101                 const s64 initialized_size)
 102 {
 103         u8 *kp = page_address(page);
 104         unsigned int kp_ofs;
 105
 106         ntfs_debug("Zeroing page region outside initialized size.");
 107         if (((s64)page->index << PAGE_CACHE_SHIFT) >= initialized_size) {
 108                 clear_page(kp);
 109                 return;
 110         }
 111         kp_ofs = initialized_size & ~PAGE_CACHE_MASK;
 112         memset(kp + kp_ofs, 0, PAGE_CACHE_SIZE - kp_ofs);
 113         return;
 114 }
 115
 116 /**
 117  * handle_bounds_compressed_page - test for&handle out of bounds compressed page
 118  */
 119 static inline void handle_bounds_compressed_page(struct page *page,
 120                 const loff_t i_size, const s64 initialized_size)
 121 {
 122         if ((page->index >= (initialized_size >> PAGE_CACHE_SHIFT)) &&
 123                         (initialized_size < i_size))
 124                 zero_partial_compressed_page(page, initialized_size);
 125         return;
 126 }
 127
 128 /**
 129  * ntfs_decompress - decompress a compression block into an array of pages
 130  * @dest_pages:         destination array of pages
 131  * @dest_index:         current index into @dest_pages (IN/OUT)
 132  * @dest_ofs:           current offset within @dest_pages[@dest_index] (IN/OUT)
 133  * @dest_max_index:     maximum index into @dest_pages (IN)
 134  * @dest_max_ofs:       maximum offset within @dest_pages[@dest_max_index] (IN)
 135  * @xpage:              the target page (-1 if none) (IN)
 136  * @xpage_done:         set to 1 if xpage was completed successfully (IN/OUT)
 137  * @cb_start:           compression block to decompress (IN)
 138  * @cb_size:            size of compression block @cb_start in bytes (IN)
 139  * @i_size:             file size when we started the read (IN)
 140  * @initialized_size:   initialized file size when we started the read (IN)
 141  *
 142  * The caller must have disabled preemption. ntfs_decompress() reenables it when
 143  * the critical section is finished.
 144  *
 145  * This decompresses the compression block @cb_start into the array of
 146  * destination pages @dest_pages starting at index @dest_index into @dest_pages
 147  * and at offset @dest_pos into the page @dest_pages[@dest_index].
 148  *
 149  * When the page @dest_pages[@xpage] is completed, @xpage_done is set to 1.
 150  * If xpage is -1 or @xpage has not been completed, @xpage_done is not modified.
 151  *
 152  * @cb_start is a pointer to the compression block which needs decompressing
 153  * and @cb_size is the size of @cb_start in bytes (8-64kiB).
 154  *
 155  * Return 0 if success or -EOVERFLOW on error in the compressed stream.
 156  * @xpage_done indicates whether the target page (@dest_pages[@xpage]) was
 157  * completed during the decompression of the compression block (@cb_start).
 158  *
 159  * Warning: This function *REQUIRES* PAGE_CACHE_SIZE >= 4096 or it will blow up
 160  * unpredicatbly! You have been warned!
 161  *
 162  * Note to hackers: This function may not sleep until it has finished accessing
 163  * the compression block @cb_start as it is a per-CPU buffer.
 164  */
 165 static int ntfs_decompress(struct page *dest_pages[], int *dest_index,
 166                 int *dest_ofs, const int dest_max_index, const int dest_max_ofs,
 167                 const int xpage, char *xpage_done, u8 *const cb_start,
 168                 const u32 cb_size, const loff_t i_size,
 169                 const s64 initialized_size)
 170 {
 171         /*
 172          * Pointers into the compressed data, i.e. the compression block (cb),
 173          * and the therein contained sub-blocks (sb).
 174          */
 175         u8 *cb_end = cb_start + cb_size; /* End of cb. */
 176         u8 *cb = cb_start;      /* Current position in cb. */
 177         u8 *cb_sb_start = cb;   /* Beginning of the current sb in the cb. */
 178         u8 *cb_sb_end;          /* End of current sb / beginning of next sb. */
 179
 180         /* Variables for uncompressed data / destination. */
 181         struct page *dp;        /* Current destination page being worked on. */
 182         u8 *dp_addr;            /* Current pointer into dp. */
 183         u8 *dp_sb_start;        /* Start of current sub-block in dp. */
 184         u8 *dp_sb_end;          /* End of current sb in dp (dp_sb_start +
 185                                    NTFS_SB_SIZE). */
 186         u16 do_sb_start;        /* @dest_ofs when starting this sub-block. */
 187         u16 do_sb_end;          /* @dest_ofs of end of this sb (do_sb_start +
 188                                    NTFS_SB_SIZE). */
 189
 190         /* Variables for tag and token parsing. */
 191         u8 tag;                 /* Current tag. */
 192         int token;              /* Loop counter for the eight tokens in tag. */
 193
 194         /* Need this because we can't sleep, so need two stages. */
 195         int completed_pages[dest_max_index - *dest_index + 1];
 196         int nr_completed_pages = 0;
 197
 198         /* Default error code. */
 199         int err = -EOVERFLOW;
 200
 201         ntfs_debug("Entering, cb_size = 0x%x.", cb_size);
 202 do_next_sb:
 203         ntfs_debug("Beginning sub-block at offset = 0x%zx in the cb.",
 204                         cb - cb_start);
 205         /*
 206          * Have we reached the end of the compression block or the end of the
 207          * decompressed data?  The latter can happen for example if the current
 208          * position in the compression block is one byte before its end so the
 209          * first two checks do not detect it.
 210          */
 211         if (cb == cb_end || !le16_to_cpup((le16*)cb) ||
 212                         (*dest_index == dest_max_index &&
 213                         *dest_ofs == dest_max_ofs)) {
 214                 int i;
 215
 216                 ntfs_debug("Completed. Returning success (0).");
 217                 err = 0;
 218 return_error:
 219                 /* We can sleep from now on, so we drop lock. */
 220                 spin_unlock(&ntfs_cb_lock);
 221                 /* Second stage: finalize completed pages. */
 222                 if (nr_completed_pages > 0) {
 223                         for (i = 0; i < nr_completed_pages; i++) {
 224                                 int di = completed_pages[i];
 225
 226                                 dp = dest_pages[di];
 227                                 /*
 228                                  * If we are outside the initialized size, zero
 229                                  * the out of bounds page range.
 230                                  */
 231                                 handle_bounds_compressed_page(dp, i_size,
 232                                                 initialized_size);
 233                                 flush_dcache_page(dp);
 234                                 kunmap(dp);
 235                                 SetPageUptodate(dp);
 236                                 unlock_page(dp);
 237                                 if (di == xpage)
 238                                         *xpage_done = 1;
 239                                 else
 240                                         page_cache_release(dp);
 241                                 dest_pages[di] = NULL;
 242                         }
 243                 }
 244                 return err;
 245         }
 246
 247         /* Setup offsets for the current sub-block destination. */
 248         do_sb_start = *dest_ofs;
 249         do_sb_end = do_sb_start + NTFS_SB_SIZE;
 250
 251         /* Check that we are still within allowed boundaries. */
 252         if (*dest_index == dest_max_index && do_sb_end > dest_max_ofs)
 253                 goto return_overflow;
 254
 255         /* Does the minimum size of a compressed sb overflow valid range? */
 256         if (cb + 6 > cb_end)
 257                 goto return_overflow;
 258
 259         /* Setup the current sub-block source pointers and validate range. */
 260         cb_sb_start = cb;
 261         cb_sb_end = cb_sb_start + (le16_to_cpup((le16*)cb) & NTFS_SB_SIZE_MASK)
 262                         + 3;
 263         if (cb_sb_end > cb_end)
 264                 goto return_overflow;
 265
 266         /* Get the current destination page. */
 267         dp = dest_pages[*dest_index];
 268         if (!dp) {
 269                 /* No page present. Skip decompression of this sub-block. */
 270                 cb = cb_sb_end;
 271
 272                 /* Advance destination position to next sub-block. */
 273                 *dest_ofs = (*dest_ofs + NTFS_SB_SIZE) & ~PAGE_CACHE_MASK;
 274                 if (!*dest_ofs && (++*dest_index > dest_max_index))
 275                         goto return_overflow;
 276                 goto do_next_sb;
 277         }
 278
 279         /* We have a valid destination page. Setup the destination pointers. */
 280         dp_addr = (u8*)page_address(dp) + do_sb_start;
 281
 282         /* Now, we are ready to process the current sub-block (sb). */
 283         if (!(le16_to_cpup((le16*)cb) & NTFS_SB_IS_COMPRESSED)) {
 284                 ntfs_debug("Found uncompressed sub-block.");
 285                 /* This sb is not compressed, just copy it into destination. */
 286
 287                 /* Advance source position to first data byte. */
 288                 cb += 2;
 289
 290                 /* An uncompressed sb must be full size. */
 291                 if (cb_sb_end - cb != NTFS_SB_SIZE)
 292                         goto return_overflow;
 293
 294                 /* Copy the block and advance the source position. */
 295                 memcpy(dp_addr, cb, NTFS_SB_SIZE);
 296                 cb += NTFS_SB_SIZE;
 297
 298                 /* Advance destination position to next sub-block. */
 299                 *dest_ofs += NTFS_SB_SIZE;
 300                 if (!(*dest_ofs &= ~PAGE_CACHE_MASK)) {
 301 finalize_page:
 302                         /*
 303                          * First stage: add current page index to array of
 304                          * completed pages.
 305                          */
 306                         completed_pages[nr_completed_pages++] = *dest_index;
 307                         if (++*dest_index > dest_max_index)
 308                                 goto return_overflow;
 309                 }
 310                 goto do_next_sb;
 311         }
 312         ntfs_debug("Found compressed sub-block.");
 313         /* This sb is compressed, decompress it into destination. */
 314
 315         /* Setup destination pointers. */
 316         dp_sb_start = dp_addr;
 317         dp_sb_end = dp_sb_start + NTFS_SB_SIZE;
 318
 319         /* Forward to the first tag in the sub-block. */
 320         cb += 2;
 321 do_next_tag:
 322         if (cb == cb_sb_end) {
 323                 /* Check if the decompressed sub-block was not full-length. */
 324                 if (dp_addr < dp_sb_end) {
 325                         int nr_bytes = do_sb_end - *dest_ofs;
 326
 327                         ntfs_debug("Filling incomplete sub-block with "
 328                                         "zeroes.");
 329                         /* Zero remainder and update destination position. */
 330                         memset(dp_addr, 0, nr_bytes);
 331                         *dest_ofs += nr_bytes;
 332                 }
 333                 /* We have finished the current sub-block. */
 334                 if (!(*dest_ofs &= ~PAGE_CACHE_MASK))
 335                         goto finalize_page;
 336                 goto do_next_sb;
 337         }
 338
 339         /* Check we are still in range. */
 340         if (cb > cb_sb_end || dp_addr > dp_sb_end)
 341                 goto return_overflow;
 342
 343         /* Get the next tag and advance to first token. */
 344         tag = *cb++;
 345
 346         /* Parse the eight tokens described by the tag. */
 347         for (token = 0; token < 8; token++, tag >>= 1) {
 348                 u16 lg, pt, length, max_non_overlap;
 349                 register u16 i;
 350                 u8 *dp_back_addr;
 351
 352                 /* Check if we are done / still in range. */
 353                 if (cb >= cb_sb_end || dp_addr > dp_sb_end)
 354                         break;
 355
 356                 /* Determine token type and parse appropriately.*/
 357                 if ((tag & NTFS_TOKEN_MASK) == NTFS_SYMBOL_TOKEN) {
 358                         /*
 359                          * We have a symbol token, copy the symbol across, and
 360                          * advance the source and destination positions.
 361                          */
 362                         *dp_addr++ = *cb++;
 363                         ++*dest_ofs;
 364
 365                         /* Continue with the next token. */
 366                         continue;
 367                 }
 368
 369                 /*
 370                  * We have a phrase token. Make sure it is not the first tag in
 371                  * the sb as this is illegal and would confuse the code below.
 372                  */
 373                 if (dp_addr == dp_sb_start)
 374                         goto return_overflow;
 375
 376                 /*
 377                  * Determine the number of bytes to go back (p) and the number
 378                  * of bytes to copy (l). We use an optimized algorithm in which
 379                  * we first calculate log2(current destination position in sb),
 380                  * which allows determination of l and p in O(1) rather than
 381                  * O(n). We just need an arch-optimized log2() function now.
 382                  */
 383                 lg = 0;
 384                 for (i = *dest_ofs - do_sb_start - 1; i >= 0x10; i >>= 1)
 385                         lg++;
 386
 387                 /* Get the phrase token into i. */
 388                 pt = le16_to_cpup((le16*)cb);
 389
 390                 /*
 391                  * Calculate starting position of the byte sequence in
 392                  * the destination using the fact that p = (pt >> (12 - lg)) + 1
 393                  * and make sure we don't go too far back.
 394                  */
 395                 dp_back_addr = dp_addr - (pt >> (12 - lg)) - 1;
 396                 if (dp_back_addr < dp_sb_start)
 397                         goto return_overflow;
 398
 399                 /* Now calculate the length of the byte sequence. */
 400                 length = (pt & (0xfff >> lg)) + 3;
 401
 402                 /* Advance destination position and verify it is in range. */
 403                 *dest_ofs += length;
 404                 if (*dest_ofs > do_sb_end)
 405                         goto return_overflow;
 406
 407                 /* The number of non-overlapping bytes. */
 408                 max_non_overlap = dp_addr - dp_back_addr;
 409
 410                 if (length <= max_non_overlap) {
 411                         /* The byte sequence doesn't overlap, just copy it. */
 412                         memcpy(dp_addr, dp_back_addr, length);
 413
 414                         /* Advance destination pointer. */
 415                         dp_addr += length;
 416                 } else {
 417                         /*
 418                          * The byte sequence does overlap, copy non-overlapping
 419                          * part and then do a slow byte by byte copy for the
 420                          * overlapping part. Also, advance the destination
 421                          * pointer.
 422                          */
 423                         memcpy(dp_addr, dp_back_addr, max_non_overlap);
 424                         dp_addr += max_non_overlap;
 425                         dp_back_addr += max_non_overlap;
 426                         length -= max_non_overlap;
 427                         while (length--)
 428                                 *dp_addr++ = *dp_back_addr++;
 429                 }
 430
 431                 /* Advance source position and continue with the next token. */
 432                 cb += 2;
 433         }
 434
 435         /* No tokens left in the current tag. Continue with the next tag. */
 436         goto do_next_tag;
 437
 438 return_overflow:
 439         ntfs_error(NULL, "Failed. Returning -EOVERFLOW.");
 440         goto return_error;
 441 }
 442
 443 int ntfs_read_compressed_block(struct page *page)
 444 {
 445         loff_t i_size;
 446         s64 initialized_size;
 447         struct address_space *mapping = page->mapping;
 448         ntfs_inode *ni = NTFS_I(mapping->host);
 449         ntfs_volume *vol = ni->vol;
 450         struct super_block *sb = vol->sb;
 451         runlist_element *rl;
 452         unsigned long flags, block_size = sb->s_blocksize;
 453         unsigned char block_size_bits = sb->s_blocksize_bits;
 454         u8 *cb, *cb_pos, *cb_end;
 455         struct buffer_head **bhs;
 456         unsigned long offset, index = page->index;
 457         u32 cb_size = ni->itype.compressed.block_size;
 458         u64 cb_size_mask = cb_size - 1UL;
 459         VCN vcn;
 460         LCN lcn;
 461         /* The first wanted vcn (minimum alignment is PAGE_CACHE_SIZE). */
 462         VCN start_vcn = (((s64)index << PAGE_CACHE_SHIFT) & ~cb_size_mask) >>
 463                         vol->cluster_size_bits;
 464         /*
 465          * The first vcn after the last wanted vcn (minumum alignment is again
 466          * PAGE_CACHE_SIZE.
 467          */
 468         VCN end_vcn = ((((s64)(index + 1UL) << PAGE_CACHE_SHIFT) + cb_size - 1)
 469                         & ~cb_size_mask) >> vol->cluster_size_bits;
 470         /* Number of compression blocks (cbs) in the wanted vcn range. */
 471         unsigned int nr_cbs = (end_vcn - start_vcn) << vol->cluster_size_bits
 472                         >> ni->itype.compressed.block_size_bits;
 473         /*
 474          * Number of pages required to store the uncompressed data from all
 475          * compression blocks (cbs) overlapping @page. Due to alignment
 476          * guarantees of start_vcn and end_vcn, no need to round up here.
 477          */
 478         unsigned int nr_pages = (end_vcn - start_vcn) <<
 479                         vol->cluster_size_bits >> PAGE_CACHE_SHIFT;
 480         unsigned int xpage, max_page, cur_page, cur_ofs, i;
 481         unsigned int cb_clusters, cb_max_ofs;
 482         int block, max_block, cb_max_page, bhs_size, nr_bhs, err = 0;
 483         struct page **pages;
 484         unsigned char xpage_done = 0;
 485
 486         ntfs_debug("Entering, page->index = 0x%lx, cb_size = 0x%x, nr_pages = "
 487                         "%i.", index, cb_size, nr_pages);
 488         /*
 489          * Bad things happen if we get here for anything that is not an
 490          * unnamed $DATA attribute.
 491          */
 492         BUG_ON(ni->type != AT_DATA);
 493         BUG_ON(ni->name_len);
 494
 495         pages = kmalloc(nr_pages * sizeof(struct page *), GFP_NOFS);
 496
 497         /* Allocate memory to store the buffer heads we need. */
 498         bhs_size = cb_size / block_size * sizeof(struct buffer_head *);
 499         bhs = kmalloc(bhs_size, GFP_NOFS);
 500
 501         if (unlikely(!pages || !bhs)) {
 502                 kfree(bhs);
 503                 kfree(pages);
 504                 unlock_page(page);
 505                 ntfs_error(vol->sb, "Failed to allocate internal buffers.");
 506                 return -ENOMEM;
 507         }
 508
 509         /*
 510          * We have already been given one page, this is the one we must do.
 511          * Once again, the alignment guarantees keep it simple.
 512          */
 513         offset = start_vcn << vol->cluster_size_bits >> PAGE_CACHE_SHIFT;
 514         xpage = index - offset;
 515         pages[xpage] = page;
 516         /*
 517          * The remaining pages need to be allocated and inserted into the page
 518          * cache, alignment guarantees keep all the below much simpler. (-8
 519          */
 520         read_lock_irqsave(&ni->size_lock, flags);
 521         i_size = i_size_read(VFS_I(ni));
 522         initialized_size = ni->initialized_size;
 523         read_unlock_irqrestore(&ni->size_lock, flags);
 524         max_page = ((i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT) -
 525                         offset;
 526         /* Is the page fully outside i_size? (truncate in progress) */
 527         if (xpage >= max_page) {
 528                 kfree(bhs);
 529                 kfree(pages);
 530                 zero_user(page, 0, PAGE_CACHE_SIZE);
 531                 ntfs_debug("Compressed read outside i_size - truncated?");
 532                 SetPageUptodate(page);
 533                 unlock_page(page);
 534                 return 0;
 535         }
 536         if (nr_pages < max_page)
 537                 max_page = nr_pages;
 538         for (i = 0; i < max_page; i++, offset++) {
 539                 if (i != xpage)
 540                         pages[i] = grab_cache_page_nowait(mapping, offset);
 541                 page = pages[i];
 542                 if (page) {
 543                         /*
 544                          * We only (re)read the page if it isn't already read
 545                          * in and/or dirty or we would be losing data or at
 546                          * least wasting our time.
 547                          */
 548                         if (!PageDirty(page) && (!PageUptodate(page) ||
 549                                         PageError(page))) {
 550                                 ClearPageError(page);
 551                                 kmap(page);
 552                                 continue;
 553                         }
 554                         unlock_page(page);
 555                         page_cache_release(page);
 556                         pages[i] = NULL;
 557                 }
 558         }
 559
 560         /*
 561          * We have the runlist, and all the destination pages we need to fill.
 562          * Now read the first compression block.
 563          */
 564         cur_page = 0;
 565         cur_ofs = 0;
 566         cb_clusters = ni->itype.compressed.block_clusters;
 567 do_next_cb:
 568         nr_cbs--;
 569         nr_bhs = 0;
 570
 571         /* Read all cb buffer heads one cluster at a time. */
 572         rl = NULL;
 573         for (vcn = start_vcn, start_vcn += cb_clusters; vcn < start_vcn;
 574                         vcn++) {
 575                 bool is_retry = false;
 576
 577                 if (!rl) {
 578 lock_retry_remap:
 579                         down_read(&ni->runlist.lock);
 580                         rl = ni->runlist.rl;
 581                 }
 582                 if (likely(rl != NULL)) {
 583                         /* Seek to element containing target vcn. */
 584                         while (rl->length && rl[1].vcn <= vcn)
 585                                 rl++;
 586                         lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
 587                 } else
 588                         lcn = LCN_RL_NOT_MAPPED;
 589                 ntfs_debug("Reading vcn = 0x%llx, lcn = 0x%llx.",
 590                                 (unsigned long long)vcn,
 591                                 (unsigned long long)lcn);
 592                 if (lcn < 0) {
 593                         /*
 594                          * When we reach the first sparse cluster we have
 595                          * finished with the cb.
 596                          */
 597                         if (lcn == LCN_HOLE)
 598                                 break;
 599                         if (is_retry || lcn != LCN_RL_NOT_MAPPED)
 600                                 goto rl_err;
 601                         is_retry = true;
 602                         /*
 603                          * Attempt to map runlist, dropping lock for the
 604                          * duration.
 605                          */
 606                         up_read(&ni->runlist.lock);
 607                         if (!ntfs_map_runlist(ni, vcn))
 608                                 goto lock_retry_remap;
 609                         goto map_rl_err;
 610                 }
 611                 block = lcn << vol->cluster_size_bits >> block_size_bits;
 612                 /* Read the lcn from device in chunks of block_size bytes. */
 613                 max_block = block + (vol->cluster_size >> block_size_bits);
 614                 do {
 615                         ntfs_debug("block = 0x%x.", block);
 616                         if (unlikely(!(bhs[nr_bhs] = sb_getblk(sb, block))))
 617                                 goto getblk_err;
 618                         nr_bhs++;
 619                 } while (++block < max_block);
 620         }
 621
 622         /* Release the lock if we took it. */
 623         if (rl)
 624                 up_read(&ni->runlist.lock);
 625
 626         /* Setup and initiate io on all buffer heads. */
 627         for (i = 0; i < nr_bhs; i++) {
 628                 struct buffer_head *tbh = bhs[i];
 629
 630                 if (!trylock_buffer(tbh))
 631                         continue;
 632                 if (unlikely(buffer_uptodate(tbh))) {
 633                         unlock_buffer(tbh);
 634                         continue;
 635                 }
 636                 get_bh(tbh);
 637                 tbh->b_end_io = end_buffer_read_sync;
 638                 submit_bh(READ, tbh);
 639         }
 640
 641         /* Wait for io completion on all buffer heads. */
 642         for (i = 0; i < nr_bhs; i++) {
 643                 struct buffer_head *tbh = bhs[i];
 644
 645                 if (buffer_uptodate(tbh))
 646                         continue;
 647                 wait_on_buffer(tbh);
 648                 /*
 649                  * We need an optimization barrier here, otherwise we start
 650                  * hitting the below fixup code when accessing a loopback
 651                  * mounted ntfs partition. This indicates either there is a
 652                  * race condition in the loop driver or, more likely, gcc
 653                  * overoptimises the code without the barrier and it doesn't
 654                  * do the Right Thing(TM).
 655                  */
 656                 barrier();
 657                 if (unlikely(!buffer_uptodate(tbh))) {
 658                         ntfs_warning(vol->sb, "Buffer is unlocked but not "
 659                                         "uptodate! Unplugging the disk queue "
 660                                         "and rescheduling.");
 661                         get_bh(tbh);
 662                         blk_run_address_space(mapping);
 663                         schedule();
 664                         put_bh(tbh);
 665                         if (unlikely(!buffer_uptodate(tbh)))
 666                                 goto read_err;
 667                         ntfs_warning(vol->sb, "Buffer is now uptodate. Good.");
 668                 }
 669         }
 670
 671         /*
 672          * Get the compression buffer. We must not sleep any more
 673          * until we are finished with it.
 674          */
 675         spin_lock(&ntfs_cb_lock);
 676         cb = ntfs_compression_buffer;
 677
 678         BUG_ON(!cb);
 679
 680         cb_pos = cb;
 681         cb_end = cb + cb_size;
 682
 683         /* Copy the buffer heads into the contiguous buffer. */
 684         for (i = 0; i < nr_bhs; i++) {
 685                 memcpy(cb_pos, bhs[i]->b_data, block_size);
 686                 cb_pos += block_size;
 687         }
 688
 689         /* Just a precaution. */
 690         if (cb_pos + 2 <= cb + cb_size)
 691                 *(u16*)cb_pos = 0;
 692
 693         /* Reset cb_pos back to the beginning. */
 694         cb_pos = cb;
 695
 696         /* We now have both source (if present) and destination. */
 697         ntfs_debug("Successfully read the compression block.");
 698
 699         /* The last page and maximum offset within it for the current cb. */
 700         cb_max_page = (cur_page << PAGE_CACHE_SHIFT) + cur_ofs + cb_size;
 701         cb_max_ofs = cb_max_page & ~PAGE_CACHE_MASK;
 702         cb_max_page >>= PAGE_CACHE_SHIFT;
 703
 704         /* Catch end of file inside a compression block. */
 705         if (cb_max_page > max_page)
 706                 cb_max_page = max_page;
 707
 708         if (vcn == start_vcn - cb_clusters) {
 709                 /* Sparse cb, zero out page range overlapping the cb. */
 710                 ntfs_debug("Found sparse compression block.");
 711                 /* We can sleep from now on, so we drop lock. */
 712                 spin_unlock(&ntfs_cb_lock);
 713                 if (cb_max_ofs)
 714                         cb_max_page--;
 715                 for (; cur_page < cb_max_page; cur_page++) {
 716                         page = pages[cur_page];
 717                         if (page) {
 718                                 if (likely(!cur_ofs))
 719                                         clear_page(page_address(page));
 720                                 else
 721                                         memset(page_address(page) + cur_ofs, 0,
 722                                                         PAGE_CACHE_SIZE -
 723                                                         cur_ofs);
 724                                 flush_dcache_page(page);
 725                                 kunmap(page);
 726                                 SetPageUptodate(page);
 727                                 unlock_page(page);
 728                                 if (cur_page == xpage)
 729                                         xpage_done = 1;
 730                                 else
 731                                         page_cache_release(page);
 732                                 pages[cur_page] = NULL;
 733                         }
 734                         cb_pos += PAGE_CACHE_SIZE - cur_ofs;
 735                         cur_ofs = 0;
 736                         if (cb_pos >= cb_end)
 737                                 break;
 738                 }
 739                 /* If we have a partial final page, deal with it now. */
 740                 if (cb_max_ofs && cb_pos < cb_end) {
 741                         page = pages[cur_page];
 742                         if (page)
 743                                 memset(page_address(page) + cur_ofs, 0,
 744                                                 cb_max_ofs - cur_ofs);
 745                         /*
 746                          * No need to update cb_pos at this stage:
 747                          *      cb_pos += cb_max_ofs - cur_ofs;
 748                          */
 749                         cur_ofs = cb_max_ofs;
 750                 }
 751         } else if (vcn == start_vcn) {
 752                 /* We can't sleep so we need two stages. */
 753                 unsigned int cur2_page = cur_page;
 754                 unsigned int cur_ofs2 = cur_ofs;
 755                 u8 *cb_pos2 = cb_pos;
 756
 757                 ntfs_debug("Found uncompressed compression block.");
 758                 /* Uncompressed cb, copy it to the destination pages. */
 759                 /*
 760                  * TODO: As a big optimization, we could detect this case
 761                  * before we read all the pages and use block_read_full_page()
 762                  * on all full pages instead (we still have to treat partial
 763                  * pages especially but at least we are getting rid of the
 764                  * synchronous io for the majority of pages.
 765                  * Or if we choose not to do the read-ahead/-behind stuff, we
 766                  * could just return block_read_full_page(pages[xpage]) as long
 767                  * as PAGE_CACHE_SIZE <= cb_size.
 768                  */
 769                 if (cb_max_ofs)
 770                         cb_max_page--;
 771                 /* First stage: copy data into destination pages. */
 772                 for (; cur_page < cb_max_page; cur_page++) {
 773                         page = pages[cur_page];
 774                         if (page)
 775                                 memcpy(page_address(page) + cur_ofs, cb_pos,
 776                                                 PAGE_CACHE_SIZE - cur_ofs);
 777                         cb_pos += PAGE_CACHE_SIZE - cur_ofs;
 778                         cur_ofs = 0;
 779                         if (cb_pos >= cb_end)
 780                                 break;
 781                 }
 782                 /* If we have a partial final page, deal with it now. */
 783                 if (cb_max_ofs && cb_pos < cb_end) {
 784                         page = pages[cur_page];
 785                         if (page)
 786                                 memcpy(page_address(page) + cur_ofs, cb_pos,
 787                                                 cb_max_ofs - cur_ofs);
 788                         cb_pos += cb_max_ofs - cur_ofs;
 789                         cur_ofs = cb_max_ofs;
 790                 }
 791                 /* We can sleep from now on, so drop lock. */
 792                 spin_unlock(&ntfs_cb_lock);
 793                 /* Second stage: finalize pages. */
 794                 for (; cur2_page < cb_max_page; cur2_page++) {
 795                         page = pages[cur2_page];
 796                         if (page) {
 797                                 /*
 798                                  * If we are outside the initialized size, zero
 799                                  * the out of bounds page range.
 800                                  */
 801                                 handle_bounds_compressed_page(page, i_size,
 802                                                 initialized_size);
 803                                 flush_dcache_page(page);
 804                                 kunmap(page);
 805                                 SetPageUptodate(page);
 806                                 unlock_page(page);
 807                                 if (cur2_page == xpage)
 808                                         xpage_done = 1;
 809                                 else
 810                                         page_cache_release(page);
 811                                 pages[cur2_page] = NULL;
 812                         }
 813                         cb_pos2 += PAGE_CACHE_SIZE - cur_ofs2;
 814                         cur_ofs2 = 0;
 815                         if (cb_pos2 >= cb_end)
 816                                 break;
 817                 }
 818         } else {
 819                 /* Compressed cb, decompress it into the destination page(s). */
 820                 unsigned int prev_cur_page = cur_page;
 821
 822                 ntfs_debug("Found compressed compression block.");
 823                 err = ntfs_decompress(pages, &cur_page, &cur_ofs,
 824                                 cb_max_page, cb_max_ofs, xpage, &xpage_done,
 825                                 cb_pos, cb_size - (cb_pos - cb), i_size,
 826                                 initialized_size);
 827                 /*
 828                  * We can sleep from now on, lock already dropped by
 829                  * ntfs_decompress().
 830                  */
 831                 if (err) {
 832                         ntfs_error(vol->sb, "ntfs_decompress() failed in inode "
 833                                         "0x%lx with error code %i. Skipping "
 834                                         "this compression block.",
 835                                         ni->mft_no, -err);
 836                         /* Release the unfinished pages. */
 837                         for (; prev_cur_page < cur_page; prev_cur_page++) {
 838                                 page = pages[prev_cur_page];
 839                                 if (page) {
 840                                         flush_dcache_page(page);
 841                                         kunmap(page);
 842                                         unlock_page(page);
 843                                         if (prev_cur_page != xpage)
 844                                                 page_cache_release(page);
 845                                         pages[prev_cur_page] = NULL;
 846                                 }
 847                         }
 848                 }
 849         }
 850
 851         /* Release the buffer heads. */
 852         for (i = 0; i < nr_bhs; i++)
 853                 brelse(bhs[i]);
 854
 855         /* Do we have more work to do? */
 856         if (nr_cbs)
 857                 goto do_next_cb;
 858
 859         /* We no longer need the list of buffer heads. */
 860         kfree(bhs);
 861
 862         /* Clean up if we have any pages left. Should never happen. */
 863         for (cur_page = 0; cur_page < max_page; cur_page++) {
 864                 page = pages[cur_page];
 865                 if (page) {
 866                         ntfs_error(vol->sb, "Still have pages left! "
 867                                         "Terminating them with extreme "
 868                                         "prejudice.  Inode 0x%lx, page index "
 869                                         "0x%lx.", ni->mft_no, page->index);
 870                         flush_dcache_page(page);
 871                         kunmap(page);
 872                         unlock_page(page);
 873                         if (cur_page != xpage)
 874                                 page_cache_release(page);
 875                         pages[cur_page] = NULL;
 876                 }
 877         }
 878
 879         /* We no longer need the list of pages. */
 880         kfree(pages);
 881
 882         /* If we have completed the requested page, we return success. */
 883         if (likely(xpage_done))
 884                 return 0;
 885
 886         ntfs_debug("Failed. Returning error code %s.", err == -EOVERFLOW ?
 887                         "EOVERFLOW" : (!err ? "EIO" : "unknown error"));
 888         return err < 0 ? err : -EIO;
 889
 890 read_err:
 891         ntfs_error(vol->sb, "IO error while reading compressed data.");
 892         /* Release the buffer heads. */
 893         for (i = 0; i < nr_bhs; i++)
 894                 brelse(bhs[i]);
 895         goto err_out;
 896
 897 map_rl_err:
 898         ntfs_error(vol->sb, "ntfs_map_runlist() failed. Cannot read "
 899                         "compression block.");
 900         goto err_out;
 901
 902 rl_err:
 903         up_read(&ni->runlist.lock);
 904         ntfs_error(vol->sb, "ntfs_rl_vcn_to_lcn() failed. Cannot read "
 905                         "compression block.");
 906         goto err_out;
 907
 908 getblk_err:
 909         up_read(&ni->runlist.lock);
 910         ntfs_error(vol->sb, "getblk() failed. Cannot read compression block.");
 911
 912 err_out:
 913         kfree(bhs);
 914         for (i = cur_page; i < max_page; i++) {
 915                 page = pages[i];
 916                 if (page) {
 917                         flush_dcache_page(page);
 918                         kunmap(page);
 919                         unlock_page(page);
 920                         if (i != xpage)
 921                                 page_cache_release(page);
 922                 }
 923         }
 924         kfree(pages);
 925         return -EIO;
 926 }