fs/squashfs/file.c

   1 /*
   2  * Squashfs - a compressed read only filesystem for Linux
   3  *
   4  * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
   5  * Phillip Lougher <phillip@lougher.demon.co.uk>
   6  *
   7  * This program is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU General Public License
   9  * as published by the Free Software Foundation; either version 2,
  10  * or (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  20  *
  21  * file.c
  22  */
  23
  24 /*
  25  * This file contains code for handling regular files.  A regular file
  26  * consists of a sequence of contiguous compressed blocks, and/or a
  27  * compressed fragment block (tail-end packed block).   The compressed size
  28  * of each datablock is stored in a block list contained within the
  29  * file inode (itself stored in one or more compressed metadata blocks).
  30  *
  31  * To speed up access to datablocks when reading 'large' files (256 Mbytes or
  32  * larger), the code implements an index cache that caches the mapping from
  33  * block index to datablock location on disk.
  34  *
  35  * The index cache allows Squashfs to handle large files (up to 1.75 TiB) while
  36  * retaining a simple and space-efficient block list on disk.  The cache
  37  * is split into slots, caching up to eight 224 GiB files (128 KiB blocks).
  38  * Larger files use multiple slots, with 1.75 TiB files using all 8 slots.
  39  * The index cache is designed to be memory efficient, and by default uses
  40  * 16 KiB.
  41  */
  42
  43 #include <linux/fs.h>
  44 #include <linux/vfs.h>
  45 #include <linux/kernel.h>
  46 #include <linux/slab.h>
  47 #include <linux/string.h>
  48 #include <linux/pagemap.h>
  49 #include <linux/mutex.h>
  50 #include <linux/zlib.h>
  51
  52 #include "squashfs_fs.h"
  53 #include "squashfs_fs_sb.h"
  54 #include "squashfs_fs_i.h"
  55 #include "squashfs.h"
  56
  57 /*
  58  * Locate cache slot in range [offset, index] for specified inode.  If
  59  * there's more than one return the slot closest to index.
  60  */
  61 static struct meta_index *locate_meta_index(struct inode *inode, int offset,
  62                                 int index)
  63 {
  64         struct meta_index *meta = NULL;
  65         struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
  66         int i;
  67
  68         mutex_lock(&msblk->meta_index_mutex);
  69
  70         TRACE("locate_meta_index: index %d, offset %d\n", index, offset);
  71
  72         if (msblk->meta_index == NULL)
  73                 goto not_allocated;
  74
  75         for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
  76                 if (msblk->meta_index[i].inode_number == inode->i_ino &&
  77                                 msblk->meta_index[i].offset >= offset &&
  78                                 msblk->meta_index[i].offset <= index &&
  79                                 msblk->meta_index[i].locked == 0) {
  80                         TRACE("locate_meta_index: entry %d, offset %d\n", i,
  81                                         msblk->meta_index[i].offset);
  82                         meta = &msblk->meta_index[i];
  83                         offset = meta->offset;
  84                 }
  85         }
  86
  87         if (meta)
  88                 meta->locked = 1;
  89
  90 not_allocated:
  91         mutex_unlock(&msblk->meta_index_mutex);
  92
  93         return meta;
  94 }
  95
  96
  97 /*
  98  * Find and initialise an empty cache slot for index offset.
  99  */
 100 static struct meta_index *empty_meta_index(struct inode *inode, int offset,
 101                                 int skip)
 102 {
 103         struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
 104         struct meta_index *meta = NULL;
 105         int i;
 106
 107         mutex_lock(&msblk->meta_index_mutex);
 108
 109         TRACE("empty_meta_index: offset %d, skip %d\n", offset, skip);
 110
 111         if (msblk->meta_index == NULL) {
 112                 /*
 113                  * First time cache index has been used, allocate and
 114                  * initialise.  The cache index could be allocated at
 115                  * mount time but doing it here means it is allocated only
 116                  * if a 'large' file is read.
 117                  */
 118                 msblk->meta_index = kcalloc(SQUASHFS_META_SLOTS,
 119                         sizeof(*(msblk->meta_index)), GFP_KERNEL);
 120                 if (msblk->meta_index == NULL) {
 121                         ERROR("Failed to allocate meta_index\n");
 122                         goto failed;
 123                 }
 124                 for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
 125                         msblk->meta_index[i].inode_number = 0;
 126                         msblk->meta_index[i].locked = 0;
 127                 }
 128                 msblk->next_meta_index = 0;
 129         }
 130
 131         for (i = SQUASHFS_META_SLOTS; i &&
 132                         msblk->meta_index[msblk->next_meta_index].locked; i--)
 133                 msblk->next_meta_index = (msblk->next_meta_index + 1) %
 134                         SQUASHFS_META_SLOTS;
 135
 136         if (i == 0) {
 137                 TRACE("empty_meta_index: failed!\n");
 138                 goto failed;
 139         }
 140
 141         TRACE("empty_meta_index: returned meta entry %d, %p\n",
 142                         msblk->next_meta_index,
 143                         &msblk->meta_index[msblk->next_meta_index]);
 144
 145         meta = &msblk->meta_index[msblk->next_meta_index];
 146         msblk->next_meta_index = (msblk->next_meta_index + 1) %
 147                         SQUASHFS_META_SLOTS;
 148
 149         meta->inode_number = inode->i_ino;
 150         meta->offset = offset;
 151         meta->skip = skip;
 152         meta->entries = 0;
 153         meta->locked = 1;
 154
 155 failed:
 156         mutex_unlock(&msblk->meta_index_mutex);
 157         return meta;
 158 }
 159
 160
 161 static void release_meta_index(struct inode *inode, struct meta_index *meta)
 162 {
 163         struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
 164         mutex_lock(&msblk->meta_index_mutex);
 165         meta->locked = 0;
 166         mutex_unlock(&msblk->meta_index_mutex);
 167 }
 168
 169
 170 /*
 171  * Read the next n blocks from the block list, starting from
 172  * metadata block <start_block, offset>.
 173  */
 174 static long long read_indexes(struct super_block *sb, int n,
 175                                 u64 *start_block, int *offset)
 176 {
 177         int err, i;
 178         long long block = 0;
 179         __le32 *blist = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
 180
 181         if (blist == NULL) {
 182                 ERROR("read_indexes: Failed to allocate block_list\n");
 183                 return -ENOMEM;
 184         }
 185
 186         while (n) {
 187                 int blocks = min_t(int, n, PAGE_CACHE_SIZE >> 2);
 188
 189                 err = squashfs_read_metadata(sb, blist, start_block,
 190                                 offset, blocks << 2);
 191                 if (err < 0) {
 192                         ERROR("read_indexes: reading block [%llx:%x]\n",
 193                                 *start_block, *offset);
 194                         goto failure;
 195                 }
 196
 197                 for (i = 0; i < blocks; i++) {
 198                         int size = le32_to_cpu(blist[i]);
 199                         block += SQUASHFS_COMPRESSED_SIZE_BLOCK(size);
 200                 }
 201                 n -= blocks;
 202         }
 203
 204         kfree(blist);
 205         return block;
 206
 207 failure:
 208         kfree(blist);
 209         return err;
 210 }
 211
 212
 213 /*
 214  * Each cache index slot has SQUASHFS_META_ENTRIES, each of which
 215  * can cache one index -> datablock/blocklist-block mapping.  We wish
 216  * to distribute these over the length of the file, entry[0] maps index x,
 217  * entry[1] maps index x + skip, entry[2] maps index x + 2 * skip, and so on.
 218  * The larger the file, the greater the skip factor.  The skip factor is
 219  * limited to the size of the metadata cache (SQUASHFS_CACHED_BLKS) to ensure
 220  * the number of metadata blocks that need to be read fits into the cache.
 221  * If the skip factor is limited in this way then the file will use multiple
 222  * slots.
 223  */
 224 static inline int calculate_skip(int blocks)
 225 {
 226         int skip = blocks / ((SQUASHFS_META_ENTRIES + 1)
 227                  * SQUASHFS_META_INDEXES);
 228         return min(SQUASHFS_CACHED_BLKS - 1, skip + 1);
 229 }
 230
 231
 232 /*
 233  * Search and grow the index cache for the specified inode, returning the
 234  * on-disk locations of the datablock and block list metadata block
 235  * <index_block, index_offset> for index (scaled to nearest cache index).
 236  */
 237 static int fill_meta_index(struct inode *inode, int index,
 238                 u64 *index_block, int *index_offset, u64 *data_block)
 239 {
 240         struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
 241         int skip = calculate_skip(i_size_read(inode) >> msblk->block_log);
 242         int offset = 0;
 243         struct meta_index *meta;
 244         struct meta_entry *meta_entry;
 245         u64 cur_index_block = squashfs_i(inode)->block_list_start;
 246         int cur_offset = squashfs_i(inode)->offset;
 247         u64 cur_data_block = squashfs_i(inode)->start;
 248         int err, i;
 249
 250         /*
 251          * Scale index to cache index (cache slot entry)
 252          */
 253         index /= SQUASHFS_META_INDEXES * skip;
 254
 255         while (offset < index) {
 256                 meta = locate_meta_index(inode, offset + 1, index);
 257
 258                 if (meta == NULL) {
 259                         meta = empty_meta_index(inode, offset + 1, skip);
 260                         if (meta == NULL)
 261                                 goto all_done;
 262                 } else {
 263                         offset = index < meta->offset + meta->entries ? index :
 264                                 meta->offset + meta->entries - 1;
 265                         meta_entry = &meta->meta_entry[offset - meta->offset];
 266                         cur_index_block = meta_entry->index_block +
 267                                 msblk->inode_table;
 268                         cur_offset = meta_entry->offset;
 269                         cur_data_block = meta_entry->data_block;
 270                         TRACE("get_meta_index: offset %d, meta->offset %d, "
 271                                 "meta->entries %d\n", offset, meta->offset,
 272                                 meta->entries);
 273                         TRACE("get_meta_index: index_block 0x%llx, offset 0x%x"
 274                                 " data_block 0x%llx\n", cur_index_block,
 275                                 cur_offset, cur_data_block);
 276                 }
 277
 278                 /*
 279                  * If necessary grow cache slot by reading block list.  Cache
 280                  * slot is extended up to index or to the end of the slot, in
 281                  * which case further slots will be used.
 282                  */
 283                 for (i = meta->offset + meta->entries; i <= index &&
 284                                 i < meta->offset + SQUASHFS_META_ENTRIES; i++) {
 285                         int blocks = skip * SQUASHFS_META_INDEXES;
 286                         long long res = read_indexes(inode->i_sb, blocks,
 287                                         &cur_index_block, &cur_offset);
 288
 289                         if (res < 0) {
 290                                 if (meta->entries == 0)
 291                                         /*
 292                                          * Don't leave an empty slot on read
 293                                          * error allocated to this inode...
 294                                          */
 295                                         meta->inode_number = 0;
 296                                 err = res;
 297                                 goto failed;
 298                         }
 299
 300                         cur_data_block += res;
 301                         meta_entry = &meta->meta_entry[i - meta->offset];
 302                         meta_entry->index_block = cur_index_block -
 303                                 msblk->inode_table;
 304                         meta_entry->offset = cur_offset;
 305                         meta_entry->data_block = cur_data_block;
 306                         meta->entries++;
 307                         offset++;
 308                 }
 309
 310                 TRACE("get_meta_index: meta->offset %d, meta->entries %d\n",
 311                                 meta->offset, meta->entries);
 312
 313                 release_meta_index(inode, meta);
 314         }
 315
 316 all_done:
 317         *index_block = cur_index_block;
 318         *index_offset = cur_offset;
 319         *data_block = cur_data_block;
 320
 321         /*
 322          * Scale cache index (cache slot entry) to index
 323          */
 324         return offset * SQUASHFS_META_INDEXES * skip;
 325
 326 failed:
 327         release_meta_index(inode, meta);
 328         return err;
 329 }
 330
 331
 332 /*
 333  * Get the on-disk location and compressed size of the datablock
 334  * specified by index.  Fill_meta_index() does most of the work.
 335  */
 336 static int read_blocklist(struct inode *inode, int index, u64 *block)
 337 {
 338         u64 start;
 339         long long blks;
 340         int offset;
 341         __le32 size;
 342         int res = fill_meta_index(inode, index, &start, &offset, block);
 343
 344         TRACE("read_blocklist: res %d, index %d, start 0x%llx, offset"
 345                        " 0x%x, block 0x%llx\n", res, index, start, offset,
 346                         *block);
 347
 348         if (res < 0)
 349                 return res;
 350
 351         /*
 352          * res contains the index of the mapping returned by fill_meta_index(),
 353          * this will likely be less than the desired index (because the
 354          * meta_index cache works at a higher granularity).  Read any
 355          * extra block indexes needed.
 356          */
 357         if (res < index) {
 358                 blks = read_indexes(inode->i_sb, index - res, &start, &offset);
 359                 if (blks < 0)
 360                         return (int) blks;
 361                 *block += blks;
 362         }
 363
 364         /*
 365          * Read length of block specified by index.
 366          */
 367         res = squashfs_read_metadata(inode->i_sb, &size, &start, &offset,
 368                         sizeof(size));
 369         if (res < 0)
 370                 return res;
 371         return le32_to_cpu(size);
 372 }
 373
 374
 375 static int squashfs_readpage(struct file *file, struct page *page)
 376 {
 377         struct inode *inode = page->mapping->host;
 378         struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
 379         int bytes, i, offset = 0, sparse = 0;
 380         struct squashfs_cache_entry *buffer = NULL;
 381         void *pageaddr;
 382
 383         int mask = (1 << (msblk->block_log - PAGE_CACHE_SHIFT)) - 1;
 384         int index = page->index >> (msblk->block_log - PAGE_CACHE_SHIFT);
 385         int start_index = page->index & ~mask;
 386         int end_index = start_index | mask;
 387         int file_end = i_size_read(inode) >> msblk->block_log;
 388
 389         TRACE("Entered squashfs_readpage, page index %lx, start block %llx\n",
 390                                 page->index, squashfs_i(inode)->start);
 391
 392         if (page->index >= ((i_size_read(inode) + PAGE_CACHE_SIZE - 1) >>
 393                                         PAGE_CACHE_SHIFT))
 394                 goto out;
 395
 396         if (index < file_end || squashfs_i(inode)->fragment_block ==
 397                                         SQUASHFS_INVALID_BLK) {
 398                 /*
 399                  * Reading a datablock from disk.  Need to read block list
 400                  * to get location and block size.
 401                  */
 402                 u64 block = 0;
 403                 int bsize = read_blocklist(inode, index, &block);
 404                 if (bsize < 0)
 405                         goto error_out;
 406
 407                 if (bsize == 0) { /* hole */
 408                         bytes = index == file_end ?
 409                                 (i_size_read(inode) & (msblk->block_size - 1)) :
 410                                  msblk->block_size;
 411                         sparse = 1;
 412                 } else {
 413                         /*
 414                          * Read and decompress datablock.
 415                          */
 416                         buffer = squashfs_get_datablock(inode->i_sb,
 417                                                                 block, bsize);
 418                         if (buffer->error) {
 419                                 ERROR("Unable to read page, block %llx, size %x"
 420                                         "\n", block, bsize);
 421                                 squashfs_cache_put(buffer);
 422                                 goto error_out;
 423                         }
 424                         bytes = buffer->length;
 425                 }
 426         } else {
 427                 /*
 428                  * Datablock is stored inside a fragment (tail-end packed
 429                  * block).
 430                  */
 431                 buffer = squashfs_get_fragment(inode->i_sb,
 432                                 squashfs_i(inode)->fragment_block,
 433                                 squashfs_i(inode)->fragment_size);
 434
 435                 if (buffer->error) {
 436                         ERROR("Unable to read page, block %llx, size %x\n",
 437                                 squashfs_i(inode)->fragment_block,
 438                                 squashfs_i(inode)->fragment_size);
 439                         squashfs_cache_put(buffer);
 440                         goto error_out;
 441                 }
 442                 bytes = i_size_read(inode) & (msblk->block_size - 1);
 443                 offset = squashfs_i(inode)->fragment_offset;
 444         }
 445
 446         /*
 447          * Loop copying datablock into pages.  As the datablock likely covers
 448          * many PAGE_CACHE_SIZE pages (default block size is 128 KiB) explicitly
 449          * grab the pages from the page cache, except for the page that we've
 450          * been called to fill.
 451          */
 452         for (i = start_index; i <= end_index && bytes > 0; i++,
 453                         bytes -= PAGE_CACHE_SIZE, offset += PAGE_CACHE_SIZE) {
 454                 struct page *push_page;
 455                 int avail = sparse ? 0 : min_t(int, bytes, PAGE_CACHE_SIZE);
 456
 457                 TRACE("bytes %d, i %d, available_bytes %d\n", bytes, i, avail);
 458
 459                 push_page = (i == page->index) ? page :
 460                         grab_cache_page_nowait(page->mapping, i);
 461
 462                 if (!push_page)
 463                         continue;
 464
 465                 if (PageUptodate(push_page))
 466                         goto skip_page;
 467
 468                 pageaddr = kmap_atomic(push_page, KM_USER0);
 469                 squashfs_copy_data(pageaddr, buffer, offset, avail);
 470                 memset(pageaddr + avail, 0, PAGE_CACHE_SIZE - avail);
 471                 kunmap_atomic(pageaddr, KM_USER0);
 472                 flush_dcache_page(push_page);
 473                 SetPageUptodate(push_page);
 474 skip_page:
 475                 unlock_page(push_page);
 476                 if (i != page->index)
 477                         page_cache_release(push_page);
 478         }
 479
 480         if (!sparse)
 481                 squashfs_cache_put(buffer);
 482
 483         return 0;
 484
 485 error_out:
 486         SetPageError(page);
 487 out:
 488         pageaddr = kmap_atomic(page, KM_USER0);
 489         memset(pageaddr, 0, PAGE_CACHE_SIZE);
 490         kunmap_atomic(pageaddr, KM_USER0);
 491         flush_dcache_page(page);
 492         if (!PageError(page))
 493                 SetPageUptodate(page);
 494         unlock_page(page);
 495
 496         return 0;
 497 }
 498
 499
 500 const struct address_space_operations squashfs_aops = {
 501         .readpage = squashfs_readpage
 502 };