fs/squashfs/cache.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  * cache.c
  22  */
  23
  24 /*
  25  * Blocks in Squashfs are compressed.  To avoid repeatedly decompressing
  26  * recently accessed data Squashfs uses two small metadata and fragment caches.
  27  *
  28  * This file implements a generic cache implementation used for both caches,
  29  * plus functions layered ontop of the generic cache implementation to
  30  * access the metadata and fragment caches.
  31  *
  32  * To avoid out of memory and fragmentation issues with vmalloc the cache
  33  * uses sequences of kmalloced PAGE_SIZE buffers.
  34  *
  35  * It should be noted that the cache is not used for file datablocks, these
  36  * are decompressed and cached in the page-cache in the normal way.  The
  37  * cache is only used to temporarily cache fragment and metadata blocks
  38  * which have been read as as a result of a metadata (i.e. inode or
  39  * directory) or fragment access.  Because metadata and fragments are packed
  40  * together into blocks (to gain greater compression) the read of a particular
  41  * piece of metadata or fragment will retrieve other metadata/fragments which
  42  * have been packed with it, these because of locality-of-reference may be read
  43  * in the near future. Temporarily caching them ensures they are available for
  44  * near future access without requiring an additional read and decompress.
  45  */
  46
  47 #include <linux/fs.h>
  48 #include <linux/vfs.h>
  49 #include <linux/slab.h>
  50 #include <linux/vmalloc.h>
  51 #include <linux/sched.h>
  52 #include <linux/spinlock.h>
  53 #include <linux/wait.h>
  54 #include <linux/pagemap.h>
  55
  56 #include "squashfs_fs.h"
  57 #include "squashfs_fs_sb.h"
  58 #include "squashfs.h"
  59 #include "page_actor.h"
  60
  61 /*
  62  * Look-up block in cache, and increment usage count.  If not in cache, read
  63  * and decompress it from disk.
  64  */
  65 struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb,
  66         struct squashfs_cache *cache, u64 block, int length)
  67 {
  68         int i, n;
  69         struct squashfs_cache_entry *entry;
  70
  71         spin_lock(&cache->lock);
  72
  73         while (1) {
  74                 for (i = cache->curr_blk, n = 0; n < cache->entries; n++) {
  75                         if (cache->entry[i].block == block) {
  76                                 cache->curr_blk = i;
  77                                 break;
  78                         }
  79                         i = (i + 1) % cache->entries;
  80                 }
  81
  82                 if (n == cache->entries) {
  83                         /*
  84                          * Block not in cache, if all cache entries are used
  85                          * go to sleep waiting for one to become available.
  86                          */
  87                         if (cache->unused == 0) {
  88                                 cache->num_waiters++;
  89                                 spin_unlock(&cache->lock);
  90                                 wait_event(cache->wait_queue, cache->unused);
  91                                 spin_lock(&cache->lock);
  92                                 cache->num_waiters--;
  93                                 continue;
  94                         }
  95
  96                         /*
  97                          * At least one unused cache entry.  A simple
  98                          * round-robin strategy is used to choose the entry to
  99                          * be evicted from the cache.
 100                          */
 101                         i = cache->next_blk;
 102                         for (n = 0; n < cache->entries; n++) {
 103                                 if (cache->entry[i].refcount == 0)
 104                                         break;
 105                                 i = (i + 1) % cache->entries;
 106                         }
 107
 108                         cache->next_blk = (i + 1) % cache->entries;
 109                         entry = &cache->entry[i];
 110
 111                         /*
 112                          * Initialise chosen cache entry, and fill it in from
 113                          * disk.
 114                          */
 115                         cache->unused--;
 116                         entry->block = block;
 117                         entry->refcount = 1;
 118                         entry->pending = 1;
 119                         entry->num_waiters = 0;
 120                         entry->error = 0;
 121                         spin_unlock(&cache->lock);
 122
 123                         entry->length = squashfs_read_data(sb, block, length,
 124                                 &entry->next_index, entry->actor);
 125
 126                         spin_lock(&cache->lock);
 127
 128                         if (entry->length < 0)
 129                                 entry->error = entry->length;
 130
 131                         entry->pending = 0;
 132
 133                         /*
 134                          * While filling this entry one or more other processes
 135                          * have looked it up in the cache, and have slept
 136                          * waiting for it to become available.
 137                          */
 138                         if (entry->num_waiters) {
 139                                 spin_unlock(&cache->lock);
 140                                 wake_up_all(&entry->wait_queue);
 141                         } else
 142                                 spin_unlock(&cache->lock);
 143
 144                         goto out;
 145                 }
 146
 147                 /*
 148                  * Block already in cache.  Increment refcount so it doesn't
 149                  * get reused until we're finished with it, if it was
 150                  * previously unused there's one less cache entry available
 151                  * for reuse.
 152                  */
 153                 entry = &cache->entry[i];
 154                 if (entry->refcount == 0)
 155                         cache->unused--;
 156                 entry->refcount++;
 157
 158                 /*
 159                  * If the entry is currently being filled in by another process
 160                  * go to sleep waiting for it to become available.
 161                  */
 162                 if (entry->pending) {
 163                         entry->num_waiters++;
 164                         spin_unlock(&cache->lock);
 165                         wait_event(entry->wait_queue, !entry->pending);
 166                 } else
 167                         spin_unlock(&cache->lock);
 168
 169                 goto out;
 170         }
 171
 172 out:
 173         TRACE("Got %s %d, start block %lld, refcount %d, error %d\n",
 174                 cache->name, i, entry->block, entry->refcount, entry->error);
 175
 176         if (entry->error)
 177                 ERROR("Unable to read %s cache entry [%llx]\n", cache->name,
 178                                                         block);
 179         return entry;
 180 }
 181
 182
 183 /*
 184  * Release cache entry, once usage count is zero it can be reused.
 185  */
 186 void squashfs_cache_put(struct squashfs_cache_entry *entry)
 187 {
 188         struct squashfs_cache *cache = entry->cache;
 189
 190         spin_lock(&cache->lock);
 191         entry->refcount--;
 192         if (entry->refcount == 0) {
 193                 cache->unused++;
 194                 /*
 195                  * If there's any processes waiting for a block to become
 196                  * available, wake one up.
 197                  */
 198                 if (cache->num_waiters) {
 199                         spin_unlock(&cache->lock);
 200                         wake_up(&cache->wait_queue);
 201                         return;
 202                 }
 203         }
 204         spin_unlock(&cache->lock);
 205 }
 206
 207 /*
 208  * Delete cache reclaiming all kmalloced buffers.
 209  */
 210 void squashfs_cache_delete(struct squashfs_cache *cache)
 211 {
 212         int i, j;
 213
 214         if (cache == NULL)
 215                 return;
 216
 217         for (i = 0; i < cache->entries; i++) {
 218                 if (cache->entry[i].data) {
 219                         for (j = 0; j < cache->pages; j++)
 220                                 kfree(cache->entry[i].data[j]);
 221                         kfree(cache->entry[i].data);
 222                 }
 223                 kfree(cache->entry[i].actor);
 224         }
 225
 226         kfree(cache->entry);
 227         kfree(cache);
 228 }
 229
 230
 231 /*
 232  * Initialise cache allocating the specified number of entries, each of
 233  * size block_size.  To avoid vmalloc fragmentation issues each entry
 234  * is allocated as a sequence of kmalloced PAGE_SIZE buffers.
 235  */
 236 struct squashfs_cache *squashfs_cache_init(char *name, int entries,
 237         int block_size)
 238 {
 239         int i, j;
 240         struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);
 241
 242         if (cache == NULL) {
 243                 ERROR("Failed to allocate %s cache\n", name);
 244                 return NULL;
 245         }
 246
 247         cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
 248         if (cache->entry == NULL) {
 249                 ERROR("Failed to allocate %s cache\n", name);
 250                 goto cleanup;
 251         }
 252
 253         cache->curr_blk = 0;
 254         cache->next_blk = 0;
 255         cache->unused = entries;
 256         cache->entries = entries;
 257         cache->block_size = block_size;
 258         cache->pages = block_size >> PAGE_SHIFT;
 259         cache->pages = cache->pages ? cache->pages : 1;
 260         cache->name = name;
 261         cache->num_waiters = 0;
 262         spin_lock_init(&cache->lock);
 263         init_waitqueue_head(&cache->wait_queue);
 264
 265         for (i = 0; i < entries; i++) {
 266                 struct squashfs_cache_entry *entry = &cache->entry[i];
 267
 268                 init_waitqueue_head(&cache->entry[i].wait_queue);
 269                 entry->cache = cache;
 270                 entry->block = SQUASHFS_INVALID_BLK;
 271                 entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL);
 272                 if (entry->data == NULL) {
 273                         ERROR("Failed to allocate %s cache entry\n", name);
 274                         goto cleanup;
 275                 }
 276
 277                 for (j = 0; j < cache->pages; j++) {
 278                         entry->data[j] = kmalloc(PAGE_SIZE, GFP_KERNEL);
 279                         if (entry->data[j] == NULL) {
 280                                 ERROR("Failed to allocate %s buffer\n", name);
 281                                 goto cleanup;
 282                         }
 283                 }
 284
 285                 entry->actor = squashfs_page_actor_init(entry->data,
 286                                                 cache->pages, 0);
 287                 if (entry->actor == NULL) {
 288                         ERROR("Failed to allocate %s cache entry\n", name);
 289                         goto cleanup;
 290                 }
 291         }
 292
 293         return cache;
 294
 295 cleanup:
 296         squashfs_cache_delete(cache);
 297         return NULL;
 298 }
 299
 300
 301 /*
 302  * Copy up to length bytes from cache entry to buffer starting at offset bytes
 303  * into the cache entry.  If there's not length bytes then copy the number of
 304  * bytes available.  In all cases return the number of bytes copied.
 305  */
 306 int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry,
 307                 int offset, int length)
 308 {
 309         int remaining = length;
 310
 311         if (length == 0)
 312                 return 0;
 313         else if (buffer == NULL)
 314                 return min(length, entry->length - offset);
 315
 316         while (offset < entry->length) {
 317                 void *buff = entry->data[offset / PAGE_SIZE]
 318                                 + (offset % PAGE_SIZE);
 319                 int bytes = min_t(int, entry->length - offset,
 320                                 PAGE_SIZE - (offset % PAGE_SIZE));
 321
 322                 if (bytes >= remaining) {
 323                         memcpy(buffer, buff, remaining);
 324                         remaining = 0;
 325                         break;
 326                 }
 327
 328                 memcpy(buffer, buff, bytes);
 329                 buffer += bytes;
 330                 remaining -= bytes;
 331                 offset += bytes;
 332         }
 333
 334         return length - remaining;
 335 }
 336
 337
 338 /*
 339  * Read length bytes from metadata position <block, offset> (block is the
 340  * start of the compressed block on disk, and offset is the offset into
 341  * the block once decompressed).  Data is packed into consecutive blocks,
 342  * and length bytes may require reading more than one block.
 343  */
 344 int squashfs_read_metadata(struct super_block *sb, void *buffer,
 345                 u64 *block, int *offset, int length)
 346 {
 347         struct squashfs_sb_info *msblk = sb->s_fs_info;
 348         int bytes, res = length;
 349         struct squashfs_cache_entry *entry;
 350
 351         TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);
 352
 353         while (length) {
 354                 entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
 355                 if (entry->error) {
 356                         res = entry->error;
 357                         goto error;
 358                 } else if (*offset >= entry->length) {
 359                         res = -EIO;
 360                         goto error;
 361                 }
 362
 363                 bytes = squashfs_copy_data(buffer, entry, *offset, length);
 364                 if (buffer)
 365                         buffer += bytes;
 366                 length -= bytes;
 367                 *offset += bytes;
 368
 369                 if (*offset == entry->length) {
 370                         *block = entry->next_index;
 371                         *offset = 0;
 372                 }
 373
 374                 squashfs_cache_put(entry);
 375         }
 376
 377         return res;
 378
 379 error:
 380         squashfs_cache_put(entry);
 381         return res;
 382 }
 383
 384
 385 /*
 386  * Look-up in the fragmment cache the fragment located at <start_block> in the
 387  * filesystem.  If necessary read and decompress it from disk.
 388  */
 389 struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
 390                                 u64 start_block, int length)
 391 {
 392         struct squashfs_sb_info *msblk = sb->s_fs_info;
 393
 394         return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
 395                 length);
 396 }
 397
 398
 399 /*
 400  * Read and decompress the datablock located at <start_block> in the
 401  * filesystem.  The cache is used here to avoid duplicating locking and
 402  * read/decompress code.
 403  */
 404 struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
 405                                 u64 start_block, int length)
 406 {
 407         struct squashfs_sb_info *msblk = sb->s_fs_info;
 408
 409         return squashfs_cache_get(sb, msblk->read_page, start_block, length);
 410 }
 411
 412
 413 /*
 414  * Read a filesystem table (uncompressed sequence of bytes) from disk
 415  */
 416 void *squashfs_read_table(struct super_block *sb, u64 block, int length)
 417 {
 418         int pages = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
 419         int i, res;
 420         void *table, *buffer, **data;
 421         struct squashfs_page_actor *actor;
 422
 423         table = buffer = kmalloc(length, GFP_KERNEL);
 424         if (table == NULL)
 425                 return ERR_PTR(-ENOMEM);
 426
 427         data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
 428         if (data == NULL) {
 429                 res = -ENOMEM;
 430                 goto failed;
 431         }
 432
 433         actor = squashfs_page_actor_init(data, pages, length);
 434         if (actor == NULL) {
 435                 res = -ENOMEM;
 436                 goto failed2;
 437         }
 438
 439         for (i = 0; i < pages; i++, buffer += PAGE_SIZE)
 440                 data[i] = buffer;
 441
 442         res = squashfs_read_data(sb, block, length |
 443                 SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, actor);
 444
 445         kfree(data);
 446         kfree(actor);
 447
 448         if (res < 0)
 449                 goto failed;
 450
 451         return table;
 452
 453 failed2:
 454         kfree(data);
 455 failed:
 456         kfree(table);
 457         return ERR_PTR(res);
 458 }