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@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  * 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 isssues with vmalloc the cache
  33  * uses sequences of kmalloced PAGE_CACHE_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_fs_i.h"
  59 #include "squashfs.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 = 0; i < cache->entries; i++)
  75                         if (cache->entry[i].block == block)
  76                                 break;
  77
  78                 if (i == cache->entries) {
  79                         /*
  80                          * Block not in cache, if all cache entries are used
  81                          * go to sleep waiting for one to become available.
  82                          */
  83                         if (cache->unused == 0) {
  84                                 cache->num_waiters++;
  85                                 spin_unlock(&cache->lock);
  86                                 wait_event(cache->wait_queue, cache->unused);
  87                                 spin_lock(&cache->lock);
  88                                 cache->num_waiters--;
  89                                 continue;
  90                         }
  91
  92                         /*
  93                          * At least one unused cache entry.  A simple
  94                          * round-robin strategy is used to choose the entry to
  95                          * be evicted from the cache.
  96                          */
  97                         i = cache->next_blk;
  98                         for (n = 0; n < cache->entries; n++) {
  99                                 if (cache->entry[i].refcount == 0)
 100                                         break;
 101                                 i = (i + 1) % cache->entries;
 102                         }
 103
 104                         cache->next_blk = (i + 1) % cache->entries;
 105                         entry = &cache->entry[i];
 106
 107                         /*
 108                          * Initialise choosen cache entry, and fill it in from
 109                          * disk.
 110                          */
 111                         cache->unused--;
 112                         entry->block = block;
 113                         entry->refcount = 1;
 114                         entry->pending = 1;
 115                         entry->num_waiters = 0;
 116                         entry->error = 0;
 117                         spin_unlock(&cache->lock);
 118
 119                         entry->length = squashfs_read_data(sb, entry->data,
 120                                 block, length, &entry->next_index,
 121                                 cache->block_size, cache->pages);
 122
 123                         spin_lock(&cache->lock);
 124
 125                         if (entry->length < 0)
 126                                 entry->error = entry->length;
 127
 128                         entry->pending = 0;
 129
 130                         /*
 131                          * While filling this entry one or more other processes
 132                          * have looked it up in the cache, and have slept
 133                          * waiting for it to become available.
 134                          */
 135                         if (entry->num_waiters) {
 136                                 spin_unlock(&cache->lock);
 137                                 wake_up_all(&entry->wait_queue);
 138                         } else
 139                                 spin_unlock(&cache->lock);
 140
 141                         goto out;
 142                 }
 143
 144                 /*
 145                  * Block already in cache.  Increment refcount so it doesn't
 146                  * get reused until we're finished with it, if it was
 147                  * previously unused there's one less cache entry available
 148                  * for reuse.
 149                  */
 150                 entry = &cache->entry[i];
 151                 if (entry->refcount == 0)
 152                         cache->unused--;
 153                 entry->refcount++;
 154
 155                 /*
 156                  * If the entry is currently being filled in by another process
 157                  * go to sleep waiting for it to become available.
 158                  */
 159                 if (entry->pending) {
 160                         entry->num_waiters++;
 161                         spin_unlock(&cache->lock);
 162                         wait_event(entry->wait_queue, !entry->pending);
 163                 } else
 164                         spin_unlock(&cache->lock);
 165
 166                 goto out;
 167         }
 168
 169 out:
 170         TRACE("Got %s %d, start block %lld, refcount %d, error %d\n",
 171                 cache->name, i, entry->block, entry->refcount, entry->error);
 172
 173         if (entry->error)
 174                 ERROR("Unable to read %s cache entry [%llx]\n", cache->name,
 175                                                         block);
 176         return entry;
 177 }
 178
 179
 180 /*
 181  * Release cache entry, once usage count is zero it can be reused.
 182  */
 183 void squashfs_cache_put(struct squashfs_cache_entry *entry)
 184 {
 185         struct squashfs_cache *cache = entry->cache;
 186
 187         spin_lock(&cache->lock);
 188         entry->refcount--;
 189         if (entry->refcount == 0) {
 190                 cache->unused++;
 191                 /*
 192                  * If there's any processes waiting for a block to become
 193                  * available, wake one up.
 194                  */
 195                 if (cache->num_waiters) {
 196                         spin_unlock(&cache->lock);
 197                         wake_up(&cache->wait_queue);
 198                         return;
 199                 }
 200         }
 201         spin_unlock(&cache->lock);
 202 }
 203
 204 /*
 205  * Delete cache reclaiming all kmalloced buffers.
 206  */
 207 void squashfs_cache_delete(struct squashfs_cache *cache)
 208 {
 209         int i, j;
 210
 211         if (cache == NULL)
 212                 return;
 213
 214         for (i = 0; i < cache->entries; i++) {
 215                 if (cache->entry[i].data) {
 216                         for (j = 0; j < cache->pages; j++)
 217                                 kfree(cache->entry[i].data[j]);
 218                         kfree(cache->entry[i].data);
 219                 }
 220         }
 221
 222         kfree(cache->entry);
 223         kfree(cache);
 224 }
 225
 226
 227 /*
 228  * Initialise cache allocating the specified number of entries, each of
 229  * size block_size.  To avoid vmalloc fragmentation issues each entry
 230  * is allocated as a sequence of kmalloced PAGE_CACHE_SIZE buffers.
 231  */
 232 struct squashfs_cache *squashfs_cache_init(char *name, int entries,
 233         int block_size)
 234 {
 235         int i, j;
 236         struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);
 237
 238         if (cache == NULL) {
 239                 ERROR("Failed to allocate %s cache\n", name);
 240                 return NULL;
 241         }
 242
 243         cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
 244         if (cache->entry == NULL) {
 245                 ERROR("Failed to allocate %s cache\n", name);
 246                 goto cleanup;
 247         }
 248
 249         cache->next_blk = 0;
 250         cache->unused = entries;
 251         cache->entries = entries;
 252         cache->block_size = block_size;
 253         cache->pages = block_size >> PAGE_CACHE_SHIFT;
 254         cache->pages = cache->pages ? cache->pages : 1;
 255         cache->name = name;
 256         cache->num_waiters = 0;
 257         spin_lock_init(&cache->lock);
 258         init_waitqueue_head(&cache->wait_queue);
 259
 260         for (i = 0; i < entries; i++) {
 261                 struct squashfs_cache_entry *entry = &cache->entry[i];
 262
 263                 init_waitqueue_head(&cache->entry[i].wait_queue);
 264                 entry->cache = cache;
 265                 entry->block = SQUASHFS_INVALID_BLK;
 266                 entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL);
 267                 if (entry->data == NULL) {
 268                         ERROR("Failed to allocate %s cache entry\n", name);
 269                         goto cleanup;
 270                 }
 271
 272                 for (j = 0; j < cache->pages; j++) {
 273                         entry->data[j] = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
 274                         if (entry->data[j] == NULL) {
 275                                 ERROR("Failed to allocate %s buffer\n", name);
 276                                 goto cleanup;
 277                         }
 278                 }
 279         }
 280
 281         return cache;
 282
 283 cleanup:
 284         squashfs_cache_delete(cache);
 285         return NULL;
 286 }
 287
 288
 289 /*
 290  * Copy upto length bytes from cache entry to buffer starting at offset bytes
 291  * into the cache entry.  If there's not length bytes then copy the number of
 292  * bytes available.  In all cases return the number of bytes copied.
 293  */
 294 int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry,
 295                 int offset, int length)
 296 {
 297         int remaining = length;
 298
 299         if (length == 0)
 300                 return 0;
 301         else if (buffer == NULL)
 302                 return min(length, entry->length - offset);
 303
 304         while (offset < entry->length) {
 305                 void *buff = entry->data[offset / PAGE_CACHE_SIZE]
 306                                 + (offset % PAGE_CACHE_SIZE);
 307                 int bytes = min_t(int, entry->length - offset,
 308                                 PAGE_CACHE_SIZE - (offset % PAGE_CACHE_SIZE));
 309
 310                 if (bytes >= remaining) {
 311                         memcpy(buffer, buff, remaining);
 312                         remaining = 0;
 313                         break;
 314                 }
 315
 316                 memcpy(buffer, buff, bytes);
 317                 buffer += bytes;
 318                 remaining -= bytes;
 319                 offset += bytes;
 320         }
 321
 322         return length - remaining;
 323 }
 324
 325
 326 /*
 327  * Read length bytes from metadata position <block, offset> (block is the
 328  * start of the compressed block on disk, and offset is the offset into
 329  * the block once decompressed).  Data is packed into consecutive blocks,
 330  * and length bytes may require reading more than one block.
 331  */
 332 int squashfs_read_metadata(struct super_block *sb, void *buffer,
 333                 u64 *block, int *offset, int length)
 334 {
 335         struct squashfs_sb_info *msblk = sb->s_fs_info;
 336         int bytes, copied = length;
 337         struct squashfs_cache_entry *entry;
 338
 339         TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);
 340
 341         while (length) {
 342                 entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
 343                 if (entry->error)
 344                         return entry->error;
 345                 else if (*offset >= entry->length)
 346                         return -EIO;
 347
 348                 bytes = squashfs_copy_data(buffer, entry, *offset, length);
 349                 if (buffer)
 350                         buffer += bytes;
 351                 length -= bytes;
 352                 *offset += bytes;
 353
 354                 if (*offset == entry->length) {
 355                         *block = entry->next_index;
 356                         *offset = 0;
 357                 }
 358
 359                 squashfs_cache_put(entry);
 360         }
 361
 362         return copied;
 363 }
 364
 365
 366 /*
 367  * Look-up in the fragmment cache the fragment located at <start_block> in the
 368  * filesystem.  If necessary read and decompress it from disk.
 369  */
 370 struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
 371                                 u64 start_block, int length)
 372 {
 373         struct squashfs_sb_info *msblk = sb->s_fs_info;
 374
 375         return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
 376                 length);
 377 }
 378
 379
 380 /*
 381  * Read and decompress the datablock located at <start_block> in the
 382  * filesystem.  The cache is used here to avoid duplicating locking and
 383  * read/decompress code.
 384  */
 385 struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
 386                                 u64 start_block, int length)
 387 {
 388         struct squashfs_sb_info *msblk = sb->s_fs_info;
 389
 390         return squashfs_cache_get(sb, msblk->read_page, start_block, length);
 391 }
 392
 393
 394 /*
 395  * Read a filesystem table (uncompressed sequence of bytes) from disk
 396  */
 397 int squashfs_read_table(struct super_block *sb, void *buffer, u64 block,
 398         int length)
 399 {
 400         int pages = (length + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 401         int i, res;
 402         void **data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
 403         if (data == NULL)
 404                 return -ENOMEM;
 405
 406         for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE)
 407                 data[i] = buffer;
 408         res = squashfs_read_data(sb, data, block, length |
 409                 SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, length, pages);
 410         kfree(data);
 411         return res;
 412 }