linux/fs/ntfs/compress.c
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   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 */
  38typedef 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 */
  61static u8 *ntfs_compression_buffer = NULL;
  62
  63/**
  64 * ntfs_cb_lock - spinlock which protects ntfs_compression_buffer
  65 */
  66static 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 */
  75int 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 */
  90void 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 */
 100static 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 */
 123static 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 */
 169static 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);
 206do_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;
 222return_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)) {
 305finalize_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;
 325do_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
 442return_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 */
 482int 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;
 606do_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) {
 617lock_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
 933read_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
 940map_rl_err:
 941        ntfs_error(vol->sb, "ntfs_map_runlist() failed. Cannot read "
 942                        "compression block.");
 943        goto err_out;
 944
 945rl_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
 951getblk_err:
 952        up_read(&ni->runlist.lock);
 953        ntfs_error(vol->sb, "getblk() failed. Cannot read compression block.");
 954
 955err_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}
 970
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