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