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.h"
  59
  60 /*
  61  * Look-up block in cache, and increment usage count.  If not in cache, read
  62  * and decompress it from disk.
  63  */
  64 struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb,
  65         struct squashfs_cache *cache, u64 block, int length)
  66 {
  67         int i, n;
  68         struct squashfs_cache_entry *entry;
  69
  70         spin_lock(&cache->lock);
  71
  72         while (1) {
  73                 for (i = 0; i < cache->entries; i++)
  74                         if (cache->entry[i].block == block)
  75                                 break;
  76
  77                 if (i == cache->entries) {
  78                         /*
  79                          * Block not in cache, if all cache entries are used
  80                          * go to sleep waiting for one to become available.
  81                          */
  82                         if (cache->unused == 0) {
  83                                 cache->num_waiters++;
  84                                 spin_unlock(&cache->lock);
  85                                 wait_event(cache->wait_queue, cache->unused);
  86                                 spin_lock(&cache->lock);
  87                                 cache->num_waiters--;
  88                                 continue;
  89                         }
  90
  91                         /*
  92                          * At least one unused cache entry.  A simple
  93                          * round-robin strategy is used to choose the entry to
  94                          * be evicted from the cache.
  95                          */
  96                         i = cache->next_blk;
  97                         for (n = 0; n < cache->entries; n++) {
  98                                 if (cache->entry[i].refcount == 0)
  99                                         break;
 100                                 i = (i + 1) % cache->entries;
 101                         }
 102
 103                         cache->next_blk = (i + 1) % cache->entries;
 104                         entry = &cache->entry[i];
 105
 106                         /*
 107                          * Initialise chosen cache entry, and fill it in from
 108                          * disk.
 109                          */
 110                         cache->unused--;
 111                         entry->block = block;
 112                         entry->refcount = 1;
 113                         entry->pending = 1;
 114                         entry->num_waiters = 0;
 115                         entry->error = 0;
 116                         spin_unlock(&cache->lock);
 117
 118                         entry->length = squashfs_read_data(sb, entry->data,
 119                                 block, length, &entry->next_index,
 120                                 cache->block_size, cache->pages);
 121
 122                         spin_lock(&cache->lock);
 123
 124                         if (entry->length < 0)
 125                                 entry->error = entry->length;
 126
 127                         entry->pending = 0;
 128
 129                         /*
 130                          * While filling this entry one or more other processes
 131                          * have looked it up in the cache, and have slept
 132                          * waiting for it to become available.
 133                          */
 134                         if (entry->num_waiters) {
 135                                 spin_unlock(&cache->lock);
 136                                 wake_up_all(&entry->wait_queue);
 137                         } else
 138                                 spin_unlock(&cache->lock);
 139
 140                         goto out;
 141                 }
 142
 143                 /*
 144                  * Block already in cache.  Increment refcount so it doesn't
 145                  * get reused until we're finished with it, if it was
 146                  * previously unused there's one less cache entry available
 147                  * for reuse.
 148                  */
 149                 entry = &cache->entry[i];
 150                 if (entry->refcount == 0)
 151                         cache->unused--;
 152                 entry->refcount++;
 153
 154                 /*
 155                  * If the entry is currently being filled in by another process
 156                  * go to sleep waiting for it to become available.
 157                  */
 158                 if (entry->pending) {
 159                         entry->num_waiters++;
 160                         spin_unlock(&cache->lock);
 161                         wait_event(entry->wait_queue, !entry->pending);
 162                 } else
 163                         spin_unlock(&cache->lock);
 164
 165                 goto out;
 166         }
 167
 168 out:
 169         TRACE("Got %s %d, start block %lld, refcount %d, error %d\n",
 170                 cache->name, i, entry->block, entry->refcount, entry->error);
 171
 172         if (entry->error)
 173                 ERROR("Unable to read %s cache entry [%llx]\n", cache->name,
 174                                                         block);
 175         return entry;
 176 }
 177
 178
 179 /*
 180  * Release cache entry, once usage count is zero it can be reused.
 181  */
 182 void squashfs_cache_put(struct squashfs_cache_entry *entry)
 183 {
 184         struct squashfs_cache *cache = entry->cache;
 185
 186         spin_lock(&cache->lock);
 187         entry->refcount--;
 188         if (entry->refcount == 0) {
 189                 cache->unused++;
 190                 /*
 191                  * If there's any processes waiting for a block to become
 192                  * available, wake one up.
 193                  */
 194                 if (cache->num_waiters) {
 195                         spin_unlock(&cache->lock);
 196                         wake_up(&cache->wait_queue);
 197                         return;
 198                 }
 199         }
 200         spin_unlock(&cache->lock);
 201 }
 202
 203 /*
 204  * Delete cache reclaiming all kmalloced buffers.
 205  */
 206 void squashfs_cache_delete(struct squashfs_cache *cache)
 207 {
 208         int i, j;
 209
 210         if (cache == NULL)
 211                 return;
 212
 213         for (i = 0; i < cache->entries; i++) {
 214                 if (cache->entry[i].data) {
 215                         for (j = 0; j < cache->pages; j++)
 216                                 kfree(cache->entry[i].data[j]);
 217                         kfree(cache->entry[i].data);
 218                 }
 219         }
 220
 221         kfree(cache->entry);
 222         kfree(cache);
 223 }
 224
 225
 226 /*
 227  * Initialise cache allocating the specified number of entries, each of
 228  * size block_size.  To avoid vmalloc fragmentation issues each entry
 229  * is allocated as a sequence of kmalloced PAGE_CACHE_SIZE buffers.
 230  */
 231 struct squashfs_cache *squashfs_cache_init(char *name, int entries,
 232         int block_size)
 233 {
 234         int i, j;
 235         struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);
 236
 237         if (cache == NULL) {
 238                 ERROR("Failed to allocate %s cache\n", name);
 239                 return NULL;
 240         }
 241
 242         cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
 243         if (cache->entry == NULL) {
 244                 ERROR("Failed to allocate %s cache\n", name);
 245                 goto cleanup;
 246         }
 247
 248         cache->next_blk = 0;
 249         cache->unused = entries;
 250         cache->entries = entries;
 251         cache->block_size = block_size;
 252         cache->pages = block_size >> PAGE_CACHE_SHIFT;
 253         cache->pages = cache->pages ? cache->pages : 1;
 254         cache->name = name;
 255         cache->num_waiters = 0;
 256         spin_lock_init(&cache->lock);
 257         init_waitqueue_head(&cache->wait_queue);
 258
 259         for (i = 0; i < entries; i++) {
 260                 struct squashfs_cache_entry *entry = &cache->entry[i];
 261
 262                 init_waitqueue_head(&cache->entry[i].wait_queue);
 263                 entry->cache = cache;
 264                 entry->block = SQUASHFS_INVALID_BLK;
 265                 entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL);
 266                 if (entry->data == NULL) {
 267                         ERROR("Failed to allocate %s cache entry\n", name);
 268                         goto cleanup;
 269                 }
 270
 271                 for (j = 0; j < cache->pages; j++) {
 272                         entry->data[j] = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
 273                         if (entry->data[j] == NULL) {
 274                                 ERROR("Failed to allocate %s buffer\n", name);
 275                                 goto cleanup;
 276                         }
 277                 }
 278         }
 279
 280         return cache;
 281
 282 cleanup:
 283         squashfs_cache_delete(cache);
 284         return NULL;
 285 }
 286
 287
 288 /*
 289  * Copy up to length bytes from cache entry to buffer starting at offset bytes
 290  * into the cache entry.  If there's not length bytes then copy the number of
 291  * bytes available.  In all cases return the number of bytes copied.
 292  */
 293 int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry,
 294                 int offset, int length)
 295 {
 296         int remaining = length;
 297
 298         if (length == 0)
 299                 return 0;
 300         else if (buffer == NULL)
 301                 return min(length, entry->length - offset);
 302
 303         while (offset < entry->length) {
 304                 void *buff = entry->data[offset / PAGE_CACHE_SIZE]
 305                                 + (offset % PAGE_CACHE_SIZE);
 306                 int bytes = min_t(int, entry->length - offset,
 307                                 PAGE_CACHE_SIZE - (offset % PAGE_CACHE_SIZE));
 308
 309                 if (bytes >= remaining) {
 310                         memcpy(buffer, buff, remaining);
 311                         remaining = 0;
 312                         break;
 313                 }
 314
 315                 memcpy(buffer, buff, bytes);
 316                 buffer += bytes;
 317                 remaining -= bytes;
 318                 offset += bytes;
 319         }
 320
 321         return length - remaining;
 322 }
 323
 324
 325 /*
 326  * Read length bytes from metadata position <block, offset> (block is the
 327  * start of the compressed block on disk, and offset is the offset into
 328  * the block once decompressed).  Data is packed into consecutive blocks,
 329  * and length bytes may require reading more than one block.
 330  */
 331 int squashfs_read_metadata(struct super_block *sb, void *buffer,
 332                 u64 *block, int *offset, int length)
 333 {
 334         struct squashfs_sb_info *msblk = sb->s_fs_info;
 335         int bytes, copied = length;
 336         struct squashfs_cache_entry *entry;
 337
 338         TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);
 339
 340         while (length) {
 341                 entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
 342                 if (entry->error)
 343                         return entry->error;
 344                 else if (*offset >= entry->length)
 345                         return -EIO;
 346
 347                 bytes = squashfs_copy_data(buffer, entry, *offset, length);
 348                 if (buffer)
 349                         buffer += bytes;
 350                 length -= bytes;
 351                 *offset += bytes;
 352
 353                 if (*offset == entry->length) {
 354                         *block = entry->next_index;
 355                         *offset = 0;
 356                 }
 357
 358                 squashfs_cache_put(entry);
 359         }
 360
 361         return copied;
 362 }
 363
 364
 365 /*
 366  * Look-up in the fragmment cache the fragment located at <start_block> in the
 367  * filesystem.  If necessary read and decompress it from disk.
 368  */
 369 struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
 370                                 u64 start_block, int length)
 371 {
 372         struct squashfs_sb_info *msblk = sb->s_fs_info;
 373
 374         return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
 375                 length);
 376 }
 377
 378
 379 /*
 380  * Read and decompress the datablock located at <start_block> in the
 381  * filesystem.  The cache is used here to avoid duplicating locking and
 382  * read/decompress code.
 383  */
 384 struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
 385                                 u64 start_block, int length)
 386 {
 387         struct squashfs_sb_info *msblk = sb->s_fs_info;
 388
 389         return squashfs_cache_get(sb, msblk->read_page, start_block, length);
 390 }
 391
 392
 393 /*
 394  * Read a filesystem table (uncompressed sequence of bytes) from disk
 395  */
 396 int squashfs_read_table(struct super_block *sb, void *buffer, u64 block,
 397         int length)
 398 {
 399         int pages = (length + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 400         int i, res;
 401         void **data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
 402         if (data == NULL)
 403                 return -ENOMEM;
 404
 405         for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE)
 406                 data[i] = buffer;
 407         res = squashfs_read_data(sb, data, block, length |
 408                 SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, length, pages);
 409         kfree(data);
 410         return res;
 411 }