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                 /*
 109                  * FIXME: Using clear_page() will become wrong when we get
 110                  * PAGE_CACHE_SIZE != PAGE_SIZE but for now there is no problem.
 111                  */
 112                 clear_page(kp);
 113                 return;
 114         }
 115         kp_ofs = initialized_size & ~PAGE_CACHE_MASK;
 116         memset(kp + kp_ofs, 0, PAGE_CACHE_SIZE - kp_ofs);
 117         return;
 118 }
 119
 120 /**
 121  * handle_bounds_compressed_page - test for&handle out of bounds compressed page
 122  */
 123 static inline void handle_bounds_compressed_page(struct page *page,
 124                 const loff_t i_size, const s64 initialized_size)
 125 {
 126         if ((page->index >= (initialized_size >> PAGE_CACHE_SHIFT)) &&
 127                         (initialized_size < i_size))
 128                 zero_partial_compressed_page(page, initialized_size);
 129         return;
 130 }
 131
 132 /**
 133  * ntfs_decompress - decompress a compression block into an array of pages
 134  * @dest_pages:         destination array of pages
 135  * @dest_index:         current index into @dest_pages (IN/OUT)
 136  * @dest_ofs:           current offset within @dest_pages[@dest_index] (IN/OUT)
 137  * @dest_max_index:     maximum index into @dest_pages (IN)
 138  * @dest_max_ofs:       maximum offset within @dest_pages[@dest_max_index] (IN)
 139  * @xpage:              the target page (-1 if none) (IN)
 140  * @xpage_done:         set to 1 if xpage was completed successfully (IN/OUT)
 141  * @cb_start:           compression block to decompress (IN)
 142  * @cb_size:            size of compression block @cb_start in bytes (IN)
 143  * @i_size:             file size when we started the read (IN)
 144  * @initialized_size:   initialized file size when we started the read (IN)
 145  *
 146  * The caller must have disabled preemption. ntfs_decompress() reenables it when
 147  * the critical section is finished.
 148  *
 149  * This decompresses the compression block @cb_start into the array of
 150  * destination pages @dest_pages starting at index @dest_index into @dest_pages
 151  * and at offset @dest_pos into the page @dest_pages[@dest_index].
 152  *
 153  * When the page @dest_pages[@xpage] is completed, @xpage_done is set to 1.
 154  * If xpage is -1 or @xpage has not been completed, @xpage_done is not modified.
 155  *
 156  * @cb_start is a pointer to the compression block which needs decompressing
 157  * and @cb_size is the size of @cb_start in bytes (8-64kiB).
 158  *
 159  * Return 0 if success or -EOVERFLOW on error in the compressed stream.
 160  * @xpage_done indicates whether the target page (@dest_pages[@xpage]) was
 161  * completed during the decompression of the compression block (@cb_start).
 162  *
 163  * Warning: This function *REQUIRES* PAGE_CACHE_SIZE >= 4096 or it will blow up
 164  * unpredicatbly! You have been warned!
 165  *
 166  * Note to hackers: This function may not sleep until it has finished accessing
 167  * the compression block @cb_start as it is a per-CPU buffer.
 168  */
 169 static int ntfs_decompress(struct page *dest_pages[], int *dest_index,
 170                 int *dest_ofs, const int dest_max_index, const int dest_max_ofs,
 171                 const int xpage, char *xpage_done, u8 *const cb_start,
 172                 const u32 cb_size, const loff_t i_size,
 173                 const s64 initialized_size)
 174 {
 175         /*
 176          * Pointers into the compressed data, i.e. the compression block (cb),
 177          * and the therein contained sub-blocks (sb).
 178          */
 179         u8 *cb_end = cb_start + cb_size; /* End of cb. */
 180         u8 *cb = cb_start;      /* Current position in cb. */
 181         u8 *cb_sb_start = cb;   /* Beginning of the current sb in the cb. */
 182         u8 *cb_sb_end;          /* End of current sb / beginning of next sb. */
 183
 184         /* Variables for uncompressed data / destination. */
 185         struct page *dp;        /* Current destination page being worked on. */
 186         u8 *dp_addr;            /* Current pointer into dp. */
 187         u8 *dp_sb_start;        /* Start of current sub-block in dp. */
 188         u8 *dp_sb_end;          /* End of current sb in dp (dp_sb_start +
 189                                    NTFS_SB_SIZE). */
 190         u16 do_sb_start;        /* @dest_ofs when starting this sub-block. */
 191         u16 do_sb_end;          /* @dest_ofs of end of this sb (do_sb_start +
 192                                    NTFS_SB_SIZE). */
 193
 194         /* Variables for tag and token parsing. */
 195         u8 tag;                 /* Current tag. */
 196         int token;              /* Loop counter for the eight tokens in tag. */
 197
 198         /* Need this because we can't sleep, so need two stages. */
 199         int completed_pages[dest_max_index - *dest_index + 1];
 200         int nr_completed_pages = 0;
 201
 202         /* Default error code. */
 203         int err = -EOVERFLOW;
 204
 205         ntfs_debug("Entering, cb_size = 0x%x.", cb_size);
 206 do_next_sb:
 207         ntfs_debug("Beginning sub-block at offset = 0x%zx in the cb.",
 208                         cb - cb_start);
 209         /*
 210          * Have we reached the end of the compression block or the end of the
 211          * decompressed data?  The latter can happen for example if the current
 212          * position in the compression block is one byte before its end so the
 213          * first two checks do not detect it.
 214          */
 215         if (cb == cb_end || !le16_to_cpup((le16*)cb) ||
 216                         (*dest_index == dest_max_index &&
 217                         *dest_ofs == dest_max_ofs)) {
 218                 int i;
 219
 220                 ntfs_debug("Completed. Returning success (0).");
 221                 err = 0;
 222 return_error:
 223                 /* We can sleep from now on, so we drop lock. */
 224                 spin_unlock(&ntfs_cb_lock);
 225                 /* Second stage: finalize completed pages. */
 226                 if (nr_completed_pages > 0) {
 227                         for (i = 0; i < nr_completed_pages; i++) {
 228                                 int di = completed_pages[i];
 229
 230                                 dp = dest_pages[di];
 231                                 /*
 232                                  * If we are outside the initialized size, zero
 233                                  * the out of bounds page range.
 234                                  */
 235                                 handle_bounds_compressed_page(dp, i_size,
 236                                                 initialized_size);
 237                                 flush_dcache_page(dp);
 238                                 kunmap(dp);
 239                                 SetPageUptodate(dp);
 240                                 unlock_page(dp);
 241                                 if (di == xpage)
 242                                         *xpage_done = 1;
 243                                 else
 244                                         page_cache_release(dp);
 245                                 dest_pages[di] = NULL;
 246                         }
 247                 }
 248                 return err;
 249         }
 250
 251         /* Setup offsets for the current sub-block destination. */
 252         do_sb_start = *dest_ofs;
 253         do_sb_end = do_sb_start + NTFS_SB_SIZE;
 254
 255         /* Check that we are still within allowed boundaries. */
 256         if (*dest_index == dest_max_index && do_sb_end > dest_max_ofs)
 257                 goto return_overflow;
 258
 259         /* Does the minimum size of a compressed sb overflow valid range? */
 260         if (cb + 6 > cb_end)
 261                 goto return_overflow;
 262
 263         /* Setup the current sub-block source pointers and validate range. */
 264         cb_sb_start = cb;
 265         cb_sb_end = cb_sb_start + (le16_to_cpup((le16*)cb) & NTFS_SB_SIZE_MASK)
 266                         + 3;
 267         if (cb_sb_end > cb_end)
 268                 goto return_overflow;
 269
 270         /* Get the current destination page. */
 271         dp = dest_pages[*dest_index];
 272         if (!dp) {
 273                 /* No page present. Skip decompression of this sub-block. */
 274                 cb = cb_sb_end;
 275
 276                 /* Advance destination position to next sub-block. */
 277                 *dest_ofs = (*dest_ofs + NTFS_SB_SIZE) & ~PAGE_CACHE_MASK;
 278                 if (!*dest_ofs && (++*dest_index > dest_max_index))
 279                         goto return_overflow;
 280                 goto do_next_sb;
 281         }
 282
 283         /* We have a valid destination page. Setup the destination pointers. */
 284         dp_addr = (u8*)page_address(dp) + do_sb_start;
 285
 286         /* Now, we are ready to process the current sub-block (sb). */
 287         if (!(le16_to_cpup((le16*)cb) & NTFS_SB_IS_COMPRESSED)) {
 288                 ntfs_debug("Found uncompressed sub-block.");
 289                 /* This sb is not compressed, just copy it into destination. */
 290
 291                 /* Advance source position to first data byte. */
 292                 cb += 2;
 293
 294                 /* An uncompressed sb must be full size. */
 295                 if (cb_sb_end - cb != NTFS_SB_SIZE)
 296                         goto return_overflow;
 297
 298                 /* Copy the block and advance the source position. */
 299                 memcpy(dp_addr, cb, NTFS_SB_SIZE);
 300                 cb += NTFS_SB_SIZE;
 301
 302                 /* Advance destination position to next sub-block. */
 303                 *dest_ofs += NTFS_SB_SIZE;
 304                 if (!(*dest_ofs &= ~PAGE_CACHE_MASK)) {
 305 finalize_page:
 306                         /*
 307                          * First stage: add current page index to array of
 308                          * completed pages.
 309                          */
 310                         completed_pages[nr_completed_pages++] = *dest_index;
 311                         if (++*dest_index > dest_max_index)
 312                                 goto return_overflow;
 313                 }
 314                 goto do_next_sb;
 315         }
 316         ntfs_debug("Found compressed sub-block.");
 317         /* This sb is compressed, decompress it into destination. */
 318
 319         /* Setup destination pointers. */
 320         dp_sb_start = dp_addr;
 321         dp_sb_end = dp_sb_start + NTFS_SB_SIZE;
 322
 323         /* Forward to the first tag in the sub-block. */
 324         cb += 2;
 325 do_next_tag:
 326         if (cb == cb_sb_end) {
 327                 /* Check if the decompressed sub-block was not full-length. */
 328                 if (dp_addr < dp_sb_end) {
 329                         int nr_bytes = do_sb_end - *dest_ofs;
 330
 331                         ntfs_debug("Filling incomplete sub-block with "
 332                                         "zeroes.");
 333                         /* Zero remainder and update destination position. */
 334                         memset(dp_addr, 0, nr_bytes);
 335                         *dest_ofs += nr_bytes;
 336                 }
 337                 /* We have finished the current sub-block. */
 338                 if (!(*dest_ofs &= ~PAGE_CACHE_MASK))
 339                         goto finalize_page;
 340                 goto do_next_sb;
 341         }
 342
 343         /* Check we are still in range. */
 344         if (cb > cb_sb_end || dp_addr > dp_sb_end)
 345                 goto return_overflow;
 346
 347         /* Get the next tag and advance to first token. */
 348         tag = *cb++;
 349
 350         /* Parse the eight tokens described by the tag. */
 351         for (token = 0; token < 8; token++, tag >>= 1) {
 352                 u16 lg, pt, length, max_non_overlap;
 353                 register u16 i;
 354                 u8 *dp_back_addr;
 355
 356                 /* Check if we are done / still in range. */
 357                 if (cb >= cb_sb_end || dp_addr > dp_sb_end)
 358                         break;
 359
 360                 /* Determine token type and parse appropriately.*/
 361                 if ((tag & NTFS_TOKEN_MASK) == NTFS_SYMBOL_TOKEN) {
 362                         /*
 363                          * We have a symbol token, copy the symbol across, and
 364                          * advance the source and destination positions.
 365                          */
 366                         *dp_addr++ = *cb++;
 367                         ++*dest_ofs;
 368
 369                         /* Continue with the next token. */
 370                         continue;
 371                 }
 372
 373                 /*
 374                  * We have a phrase token. Make sure it is not the first tag in
 375                  * the sb as this is illegal and would confuse the code below.
 376                  */
 377                 if (dp_addr == dp_sb_start)
 378                         goto return_overflow;
 379
 380                 /*
 381                  * Determine the number of bytes to go back (p) and the number
 382                  * of bytes to copy (l). We use an optimized algorithm in which
 383                  * we first calculate log2(current destination position in sb),
 384                  * which allows determination of l and p in O(1) rather than
 385                  * O(n). We just need an arch-optimized log2() function now.
 386                  */
 387                 lg = 0;
 388                 for (i = *dest_ofs - do_sb_start - 1; i >= 0x10; i >>= 1)
 389                         lg++;
 390
 391                 /* Get the phrase token into i. */
 392                 pt = le16_to_cpup((le16*)cb);
 393
 394                 /*
 395                  * Calculate starting position of the byte sequence in
 396                  * the destination using the fact that p = (pt >> (12 - lg)) + 1
 397                  * and make sure we don't go too far back.
 398                  */
 399                 dp_back_addr = dp_addr - (pt >> (12 - lg)) - 1;
 400                 if (dp_back_addr < dp_sb_start)
 401                         goto return_overflow;
 402
 403                 /* Now calculate the length of the byte sequence. */
 404                 length = (pt & (0xfff >> lg)) + 3;
 405
 406                 /* Advance destination position and verify it is in range. */
 407                 *dest_ofs += length;
 408                 if (*dest_ofs > do_sb_end)
 409                         goto return_overflow;
 410
 411                 /* The number of non-overlapping bytes. */
 412                 max_non_overlap = dp_addr - dp_back_addr;
 413
 414                 if (length <= max_non_overlap) {
 415                         /* The byte sequence doesn't overlap, just copy it. */
 416                         memcpy(dp_addr, dp_back_addr, length);
 417
 418                         /* Advance destination pointer. */
 419                         dp_addr += length;
 420                 } else {
 421                         /*
 422                          * The byte sequence does overlap, copy non-overlapping
 423                          * part and then do a slow byte by byte copy for the
 424                          * overlapping part. Also, advance the destination
 425                          * pointer.
 426                          */
 427                         memcpy(dp_addr, dp_back_addr, max_non_overlap);
 428                         dp_addr += max_non_overlap;
 429                         dp_back_addr += max_non_overlap;
 430                         length -= max_non_overlap;
 431                         while (length--)
 432                                 *dp_addr++ = *dp_back_addr++;
 433                 }
 434
 435                 /* Advance source position and continue with the next token. */
 436                 cb += 2;
 437         }
 438
 439         /* No tokens left in the current tag. Continue with the next tag. */
 440         goto do_next_tag;
 441
 442 return_overflow:
 443         ntfs_error(NULL, "Failed. Returning -EOVERFLOW.");
 444         goto return_error;
 445 }
 446
 447 /**
 448  * ntfs_read_compressed_block - read a compressed block into the page cache
 449  * @page:       locked page in the compression block(s) we need to read
 450  *
 451  * When we are called the page has already been verified to be locked and the
 452  * attribute is known to be non-resident, not encrypted, but compressed.
 453  *
 454  * 1. Determine which compression block(s) @page is in.
 455  * 2. Get hold of all pages corresponding to this/these compression block(s).
 456  * 3. Read the (first) compression block.
 457  * 4. Decompress it into the corresponding pages.
 458  * 5. Throw the compressed data away and proceed to 3. for the next compression
 459  *    block or return success if no more compression blocks left.
 460  *
 461  * Warning: We have to be careful what we do about existing pages. They might
 462  * have been written to so that we would lose data if we were to just overwrite
 463  * them with the out-of-date uncompressed data.
 464  *
 465  * FIXME: For PAGE_CACHE_SIZE > cb_size we are not doing the Right Thing(TM) at
 466  * the end of the file I think. We need to detect this case and zero the out
 467  * of bounds remainder of the page in question and mark it as handled. At the
 468  * moment we would just return -EIO on such a page. This bug will only become
 469  * apparent if pages are above 8kiB and the NTFS volume only uses 512 byte
 470  * clusters so is probably not going to be seen by anyone. Still this should
 471  * be fixed. (AIA)
 472  *
 473  * FIXME: Again for PAGE_CACHE_SIZE > cb_size we are screwing up both in
 474  * handling sparse and compressed cbs. (AIA)
 475  *
 476  * FIXME: At the moment we don't do any zeroing out in the case that
 477  * initialized_size is less than data_size. This should be safe because of the
 478  * nature of the compression algorithm used. Just in case we check and output
 479  * an error message in read inode if the two sizes are not equal for a
 480  * compressed file. (AIA)
 481  */
 482 int ntfs_read_compressed_block(struct page *page)
 483 {
 484         loff_t i_size;
 485         s64 initialized_size;
 486         struct address_space *mapping = page->mapping;
 487         ntfs_inode *ni = NTFS_I(mapping->host);
 488         ntfs_volume *vol = ni->vol;
 489         struct super_block *sb = vol->sb;
 490         runlist_element *rl;
 491         unsigned long flags, block_size = sb->s_blocksize;
 492         unsigned char block_size_bits = sb->s_blocksize_bits;
 493         u8 *cb, *cb_pos, *cb_end;
 494         struct buffer_head **bhs;
 495         unsigned long offset, index = page->index;
 496         u32 cb_size = ni->itype.compressed.block_size;
 497         u64 cb_size_mask = cb_size - 1UL;
 498         VCN vcn;
 499         LCN lcn;
 500         /* The first wanted vcn (minimum alignment is PAGE_CACHE_SIZE). */
 501         VCN start_vcn = (((s64)index << PAGE_CACHE_SHIFT) & ~cb_size_mask) >>
 502                         vol->cluster_size_bits;
 503         /*
 504          * The first vcn after the last wanted vcn (minimum alignment is again
 505          * PAGE_CACHE_SIZE.
 506          */
 507         VCN end_vcn = ((((s64)(index + 1UL) << PAGE_CACHE_SHIFT) + cb_size - 1)
 508                         & ~cb_size_mask) >> vol->cluster_size_bits;
 509         /* Number of compression blocks (cbs) in the wanted vcn range. */
 510         unsigned int nr_cbs = (end_vcn - start_vcn) << vol->cluster_size_bits
 511                         >> ni->itype.compressed.block_size_bits;
 512         /*
 513          * Number of pages required to store the uncompressed data from all
 514          * compression blocks (cbs) overlapping @page. Due to alignment
 515          * guarantees of start_vcn and end_vcn, no need to round up here.
 516          */
 517         unsigned int nr_pages = (end_vcn - start_vcn) <<
 518                         vol->cluster_size_bits >> PAGE_CACHE_SHIFT;
 519         unsigned int xpage, max_page, cur_page, cur_ofs, i;
 520         unsigned int cb_clusters, cb_max_ofs;
 521         int block, max_block, cb_max_page, bhs_size, nr_bhs, err = 0;
 522         struct page **pages;
 523         unsigned char xpage_done = 0;
 524
 525         ntfs_debug("Entering, page->index = 0x%lx, cb_size = 0x%x, nr_pages = "
 526                         "%i.", index, cb_size, nr_pages);
 527         /*
 528          * Bad things happen if we get here for anything that is not an
 529          * unnamed $DATA attribute.
 530          */
 531         BUG_ON(ni->type != AT_DATA);
 532         BUG_ON(ni->name_len);
 533
 534         pages = kmalloc(nr_pages * sizeof(struct page *), GFP_NOFS);
 535
 536         /* Allocate memory to store the buffer heads we need. */
 537         bhs_size = cb_size / block_size * sizeof(struct buffer_head *);
 538         bhs = kmalloc(bhs_size, GFP_NOFS);
 539
 540         if (unlikely(!pages || !bhs)) {
 541                 kfree(bhs);
 542                 kfree(pages);
 543                 unlock_page(page);
 544                 ntfs_error(vol->sb, "Failed to allocate internal buffers.");
 545                 return -ENOMEM;
 546         }
 547
 548         /*
 549          * We have already been given one page, this is the one we must do.
 550          * Once again, the alignment guarantees keep it simple.
 551          */
 552         offset = start_vcn << vol->cluster_size_bits >> PAGE_CACHE_SHIFT;
 553         xpage = index - offset;
 554         pages[xpage] = page;
 555         /*
 556          * The remaining pages need to be allocated and inserted into the page
 557          * cache, alignment guarantees keep all the below much simpler. (-8
 558          */
 559         read_lock_irqsave(&ni->size_lock, flags);
 560         i_size = i_size_read(VFS_I(ni));
 561         initialized_size = ni->initialized_size;
 562         read_unlock_irqrestore(&ni->size_lock, flags);
 563         max_page = ((i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT) -
 564                         offset;
 565         /* Is the page fully outside i_size? (truncate in progress) */
 566         if (xpage >= max_page) {
 567                 kfree(bhs);
 568                 kfree(pages);
 569                 zero_user(page, 0, PAGE_CACHE_SIZE);
 570                 ntfs_debug("Compressed read outside i_size - truncated?");
 571                 SetPageUptodate(page);
 572                 unlock_page(page);
 573                 return 0;
 574         }
 575         if (nr_pages < max_page)
 576                 max_page = nr_pages;
 577         for (i = 0; i < max_page; i++, offset++) {
 578                 if (i != xpage)
 579                         pages[i] = grab_cache_page_nowait(mapping, offset);
 580                 page = pages[i];
 581                 if (page) {
 582                         /*
 583                          * We only (re)read the page if it isn't already read
 584                          * in and/or dirty or we would be losing data or at
 585                          * least wasting our time.
 586                          */
 587                         if (!PageDirty(page) && (!PageUptodate(page) ||
 588                                         PageError(page))) {
 589                                 ClearPageError(page);
 590                                 kmap(page);
 591                                 continue;
 592                         }
 593                         unlock_page(page);
 594                         page_cache_release(page);
 595                         pages[i] = NULL;
 596                 }
 597         }
 598
 599         /*
 600          * We have the runlist, and all the destination pages we need to fill.
 601          * Now read the first compression block.
 602          */
 603         cur_page = 0;
 604         cur_ofs = 0;
 605         cb_clusters = ni->itype.compressed.block_clusters;
 606 do_next_cb:
 607         nr_cbs--;
 608         nr_bhs = 0;
 609
 610         /* Read all cb buffer heads one cluster at a time. */
 611         rl = NULL;
 612         for (vcn = start_vcn, start_vcn += cb_clusters; vcn < start_vcn;
 613                         vcn++) {
 614                 bool is_retry = false;
 615
 616                 if (!rl) {
 617 lock_retry_remap:
 618                         down_read(&ni->runlist.lock);
 619                         rl = ni->runlist.rl;
 620                 }
 621                 if (likely(rl != NULL)) {
 622                         /* Seek to element containing target vcn. */
 623                         while (rl->length && rl[1].vcn <= vcn)
 624                                 rl++;
 625                         lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
 626                 } else
 627                         lcn = LCN_RL_NOT_MAPPED;
 628                 ntfs_debug("Reading vcn = 0x%llx, lcn = 0x%llx.",
 629                                 (unsigned long long)vcn,
 630                                 (unsigned long long)lcn);
 631                 if (lcn < 0) {
 632                         /*
 633                          * When we reach the first sparse cluster we have
 634                          * finished with the cb.
 635                          */
 636                         if (lcn == LCN_HOLE)
 637                                 break;
 638                         if (is_retry || lcn != LCN_RL_NOT_MAPPED)
 639                                 goto rl_err;
 640                         is_retry = true;
 641                         /*
 642                          * Attempt to map runlist, dropping lock for the
 643                          * duration.
 644                          */
 645                         up_read(&ni->runlist.lock);
 646                         if (!ntfs_map_runlist(ni, vcn))
 647                                 goto lock_retry_remap;
 648                         goto map_rl_err;
 649                 }
 650                 block = lcn << vol->cluster_size_bits >> block_size_bits;
 651                 /* Read the lcn from device in chunks of block_size bytes. */
 652                 max_block = block + (vol->cluster_size >> block_size_bits);
 653                 do {
 654                         ntfs_debug("block = 0x%x.", block);
 655                         if (unlikely(!(bhs[nr_bhs] = sb_getblk(sb, block))))
 656                                 goto getblk_err;
 657                         nr_bhs++;
 658                 } while (++block < max_block);
 659         }
 660
 661         /* Release the lock if we took it. */
 662         if (rl)
 663                 up_read(&ni->runlist.lock);
 664
 665         /* Setup and initiate io on all buffer heads. */
 666         for (i = 0; i < nr_bhs; i++) {
 667                 struct buffer_head *tbh = bhs[i];
 668
 669                 if (!trylock_buffer(tbh))
 670                         continue;
 671                 if (unlikely(buffer_uptodate(tbh))) {
 672                         unlock_buffer(tbh);
 673                         continue;
 674                 }
 675                 get_bh(tbh);
 676                 tbh->b_end_io = end_buffer_read_sync;
 677                 submit_bh(READ, tbh);
 678         }
 679
 680         /* Wait for io completion on all buffer heads. */
 681         for (i = 0; i < nr_bhs; i++) {
 682                 struct buffer_head *tbh = bhs[i];
 683
 684                 if (buffer_uptodate(tbh))
 685                         continue;
 686                 wait_on_buffer(tbh);
 687                 /*
 688                  * We need an optimization barrier here, otherwise we start
 689                  * hitting the below fixup code when accessing a loopback
 690                  * mounted ntfs partition. This indicates either there is a
 691                  * race condition in the loop driver or, more likely, gcc
 692                  * overoptimises the code without the barrier and it doesn't
 693                  * do the Right Thing(TM).
 694                  */
 695                 barrier();
 696                 if (unlikely(!buffer_uptodate(tbh))) {
 697                         ntfs_warning(vol->sb, "Buffer is unlocked but not "
 698                                         "uptodate! Unplugging the disk queue "
 699                                         "and rescheduling.");
 700                         get_bh(tbh);
 701                         io_schedule();
 702                         put_bh(tbh);
 703                         if (unlikely(!buffer_uptodate(tbh)))
 704                                 goto read_err;
 705                         ntfs_warning(vol->sb, "Buffer is now uptodate. Good.");
 706                 }
 707         }
 708
 709         /*
 710          * Get the compression buffer. We must not sleep any more
 711          * until we are finished with it.
 712          */
 713         spin_lock(&ntfs_cb_lock);
 714         cb = ntfs_compression_buffer;
 715
 716         BUG_ON(!cb);
 717
 718         cb_pos = cb;
 719         cb_end = cb + cb_size;
 720
 721         /* Copy the buffer heads into the contiguous buffer. */
 722         for (i = 0; i < nr_bhs; i++) {
 723                 memcpy(cb_pos, bhs[i]->b_data, block_size);
 724                 cb_pos += block_size;
 725         }
 726
 727         /* Just a precaution. */
 728         if (cb_pos + 2 <= cb + cb_size)
 729                 *(u16*)cb_pos = 0;
 730
 731         /* Reset cb_pos back to the beginning. */
 732         cb_pos = cb;
 733
 734         /* We now have both source (if present) and destination. */
 735         ntfs_debug("Successfully read the compression block.");
 736
 737         /* The last page and maximum offset within it for the current cb. */
 738         cb_max_page = (cur_page << PAGE_CACHE_SHIFT) + cur_ofs + cb_size;
 739         cb_max_ofs = cb_max_page & ~PAGE_CACHE_MASK;
 740         cb_max_page >>= PAGE_CACHE_SHIFT;
 741
 742         /* Catch end of file inside a compression block. */
 743         if (cb_max_page > max_page)
 744                 cb_max_page = max_page;
 745
 746         if (vcn == start_vcn - cb_clusters) {
 747                 /* Sparse cb, zero out page range overlapping the cb. */
 748                 ntfs_debug("Found sparse compression block.");
 749                 /* We can sleep from now on, so we drop lock. */
 750                 spin_unlock(&ntfs_cb_lock);
 751                 if (cb_max_ofs)
 752                         cb_max_page--;
 753                 for (; cur_page < cb_max_page; cur_page++) {
 754                         page = pages[cur_page];
 755                         if (page) {
 756                                 /*
 757                                  * FIXME: Using clear_page() will become wrong
 758                                  * when we get PAGE_CACHE_SIZE != PAGE_SIZE but
 759                                  * for now there is no problem.
 760                                  */
 761                                 if (likely(!cur_ofs))
 762                                         clear_page(page_address(page));
 763                                 else
 764                                         memset(page_address(page) + cur_ofs, 0,
 765                                                         PAGE_CACHE_SIZE -
 766                                                         cur_ofs);
 767                                 flush_dcache_page(page);
 768                                 kunmap(page);
 769                                 SetPageUptodate(page);
 770                                 unlock_page(page);
 771                                 if (cur_page == xpage)
 772                                         xpage_done = 1;
 773                                 else
 774                                         page_cache_release(page);
 775                                 pages[cur_page] = NULL;
 776                         }
 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                                 memset(page_address(page) + cur_ofs, 0,
 787                                                 cb_max_ofs - cur_ofs);
 788                         /*
 789                          * No need to update cb_pos at this stage:
 790                          *      cb_pos += cb_max_ofs - cur_ofs;
 791                          */
 792                         cur_ofs = cb_max_ofs;
 793                 }
 794         } else if (vcn == start_vcn) {
 795                 /* We can't sleep so we need two stages. */
 796                 unsigned int cur2_page = cur_page;
 797                 unsigned int cur_ofs2 = cur_ofs;
 798                 u8 *cb_pos2 = cb_pos;
 799
 800                 ntfs_debug("Found uncompressed compression block.");
 801                 /* Uncompressed cb, copy it to the destination pages. */
 802                 /*
 803                  * TODO: As a big optimization, we could detect this case
 804                  * before we read all the pages and use block_read_full_page()
 805                  * on all full pages instead (we still have to treat partial
 806                  * pages especially but at least we are getting rid of the
 807                  * synchronous io for the majority of pages.
 808                  * Or if we choose not to do the read-ahead/-behind stuff, we
 809                  * could just return block_read_full_page(pages[xpage]) as long
 810                  * as PAGE_CACHE_SIZE <= cb_size.
 811                  */
 812                 if (cb_max_ofs)
 813                         cb_max_page--;
 814                 /* First stage: copy data into destination pages. */
 815                 for (; cur_page < cb_max_page; cur_page++) {
 816                         page = pages[cur_page];
 817                         if (page)
 818                                 memcpy(page_address(page) + cur_ofs, cb_pos,
 819                                                 PAGE_CACHE_SIZE - cur_ofs);
 820                         cb_pos += PAGE_CACHE_SIZE - cur_ofs;
 821                         cur_ofs = 0;
 822                         if (cb_pos >= cb_end)
 823                                 break;
 824                 }
 825                 /* If we have a partial final page, deal with it now. */
 826                 if (cb_max_ofs && cb_pos < cb_end) {
 827                         page = pages[cur_page];
 828                         if (page)
 829                                 memcpy(page_address(page) + cur_ofs, cb_pos,
 830                                                 cb_max_ofs - cur_ofs);
 831                         cb_pos += cb_max_ofs - cur_ofs;
 832                         cur_ofs = cb_max_ofs;
 833                 }
 834                 /* We can sleep from now on, so drop lock. */
 835                 spin_unlock(&ntfs_cb_lock);
 836                 /* Second stage: finalize pages. */
 837                 for (; cur2_page < cb_max_page; cur2_page++) {
 838                         page = pages[cur2_page];
 839                         if (page) {
 840                                 /*
 841                                  * If we are outside the initialized size, zero
 842                                  * the out of bounds page range.
 843                                  */
 844                                 handle_bounds_compressed_page(page, i_size,
 845                                                 initialized_size);
 846                                 flush_dcache_page(page);
 847                                 kunmap(page);
 848                                 SetPageUptodate(page);
 849                                 unlock_page(page);
 850                                 if (cur2_page == xpage)
 851                                         xpage_done = 1;
 852                                 else
 853                                         page_cache_release(page);
 854                                 pages[cur2_page] = NULL;
 855                         }
 856                         cb_pos2 += PAGE_CACHE_SIZE - cur_ofs2;
 857                         cur_ofs2 = 0;
 858                         if (cb_pos2 >= cb_end)
 859                                 break;
 860                 }
 861         } else {
 862                 /* Compressed cb, decompress it into the destination page(s). */
 863                 unsigned int prev_cur_page = cur_page;
 864
 865                 ntfs_debug("Found compressed compression block.");
 866                 err = ntfs_decompress(pages, &cur_page, &cur_ofs,
 867                                 cb_max_page, cb_max_ofs, xpage, &xpage_done,
 868                                 cb_pos, cb_size - (cb_pos - cb), i_size,
 869                                 initialized_size);
 870                 /*
 871                  * We can sleep from now on, lock already dropped by
 872                  * ntfs_decompress().
 873                  */
 874                 if (err) {
 875                         ntfs_error(vol->sb, "ntfs_decompress() failed in inode "
 876                                         "0x%lx with error code %i. Skipping "
 877                                         "this compression block.",
 878                                         ni->mft_no, -err);
 879                         /* Release the unfinished pages. */
 880                         for (; prev_cur_page < cur_page; prev_cur_page++) {
 881                                 page = pages[prev_cur_page];
 882                                 if (page) {
 883                                         flush_dcache_page(page);
 884                                         kunmap(page);
 885                                         unlock_page(page);
 886                                         if (prev_cur_page != xpage)
 887                                                 page_cache_release(page);
 888                                         pages[prev_cur_page] = NULL;
 889                                 }
 890                         }
 891                 }
 892         }
 893
 894         /* Release the buffer heads. */
 895         for (i = 0; i < nr_bhs; i++)
 896                 brelse(bhs[i]);
 897
 898         /* Do we have more work to do? */
 899         if (nr_cbs)
 900                 goto do_next_cb;
 901
 902         /* We no longer need the list of buffer heads. */
 903         kfree(bhs);
 904
 905         /* Clean up if we have any pages left. Should never happen. */
 906         for (cur_page = 0; cur_page < max_page; cur_page++) {
 907                 page = pages[cur_page];
 908                 if (page) {
 909                         ntfs_error(vol->sb, "Still have pages left! "
 910                                         "Terminating them with extreme "
 911                                         "prejudice.  Inode 0x%lx, page index "
 912                                         "0x%lx.", ni->mft_no, page->index);
 913                         flush_dcache_page(page);
 914                         kunmap(page);
 915                         unlock_page(page);
 916                         if (cur_page != xpage)
 917                                 page_cache_release(page);
 918                         pages[cur_page] = NULL;
 919                 }
 920         }
 921
 922         /* We no longer need the list of pages. */
 923         kfree(pages);
 924
 925         /* If we have completed the requested page, we return success. */
 926         if (likely(xpage_done))
 927                 return 0;
 928
 929         ntfs_debug("Failed. Returning error code %s.", err == -EOVERFLOW ?
 930                         "EOVERFLOW" : (!err ? "EIO" : "unknown error"));
 931         return err < 0 ? err : -EIO;
 932
 933 read_err:
 934         ntfs_error(vol->sb, "IO error while reading compressed data.");
 935         /* Release the buffer heads. */
 936         for (i = 0; i < nr_bhs; i++)
 937                 brelse(bhs[i]);
 938         goto err_out;
 939
 940 map_rl_err:
 941         ntfs_error(vol->sb, "ntfs_map_runlist() failed. Cannot read "
 942                         "compression block.");
 943         goto err_out;
 944
 945 rl_err:
 946         up_read(&ni->runlist.lock);
 947         ntfs_error(vol->sb, "ntfs_rl_vcn_to_lcn() failed. Cannot read "
 948                         "compression block.");
 949         goto err_out;
 950
 951 getblk_err:
 952         up_read(&ni->runlist.lock);
 953         ntfs_error(vol->sb, "getblk() failed. Cannot read compression block.");
 954
 955 err_out:
 956         kfree(bhs);
 957         for (i = cur_page; i < max_page; i++) {
 958                 page = pages[i];
 959                 if (page) {
 960                         flush_dcache_page(page);
 961                         kunmap(page);
 962                         unlock_page(page);
 963                         if (i != xpage)
 964                                 page_cache_release(page);
 965                 }
 966         }
 967         kfree(pages);
 968         return -EIO;
 969 }