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_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 = cache->curr_blk, n = 0; n < cache->entries; n++) { 74 if (cache->entry[i].block == block) { 75 cache->curr_blk = i; 76 break; 77 } 78 i = (i + 1) % cache->entries; 79 } 80 81 if (n == cache->entries) { 82 /* 83 * Block not in cache, if all cache entries are used 84 * go to sleep waiting for one to become available. 85 */ 86 if (cache->unused == 0) { 87 cache->num_waiters++; 88 spin_unlock(&cache->lock); 89 wait_event(cache->wait_queue, cache->unused); 90 spin_lock(&cache->lock); 91 cache->num_waiters--; 92 continue; 93 } 94 95 /* 96 * At least one unused cache entry. A simple 97 * round-robin strategy is used to choose the entry to 98 * be evicted from the cache. 99 */ 100 i = cache->next_blk; 101 for (n = 0; n < cache->entries; n++) { 102 if (cache->entry[i].refcount == 0) 103 break; 104 i = (i + 1) % cache->entries; 105 } 106 107 cache->next_blk = (i + 1) % cache->entries; 108 entry = &cache->entry[i]; 109 110 /* 111 * Initialise chosen cache entry, and fill it in from 112 * disk. 113 */ 114 cache->unused--; 115 entry->block = block; 116 entry->refcount = 1; 117 entry->pending = 1; 118 entry->num_waiters = 0; 119 entry->error = 0; 120 spin_unlock(&cache->lock); 121 122 entry->length = squashfs_read_data(sb, entry->data, 123 block, length, &entry->next_index, 124 cache->block_size, cache->pages); 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 } 224 225 kfree(cache->entry); 226 kfree(cache); 227 } 228 229 230 /* 231 * Initialise cache allocating the specified number of entries, each of 232 * size block_size. To avoid vmalloc fragmentation issues each entry 233 * is allocated as a sequence of kmalloced PAGE_CACHE_SIZE buffers. 234 */ 235 struct squashfs_cache *squashfs_cache_init(char *name, int entries, 236 int block_size) 237 { 238 int i, j; 239 struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL); 240 241 if (cache == NULL) { 242 ERROR("Failed to allocate %s cache\n", name); 243 return NULL; 244 } 245 246 cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL); 247 if (cache->entry == NULL) { 248 ERROR("Failed to allocate %s cache\n", name); 249 goto cleanup; 250 } 251 252 cache->curr_blk = 0; 253 cache->next_blk = 0; 254 cache->unused = entries; 255 cache->entries = entries; 256 cache->block_size = block_size; 257 cache->pages = block_size >> PAGE_CACHE_SHIFT; 258 cache->pages = cache->pages ? cache->pages : 1; 259 cache->name = name; 260 cache->num_waiters = 0; 261 spin_lock_init(&cache->lock); 262 init_waitqueue_head(&cache->wait_queue); 263 264 for (i = 0; i < entries; i++) { 265 struct squashfs_cache_entry *entry = &cache->entry[i]; 266 267 init_waitqueue_head(&cache->entry[i].wait_queue); 268 entry->cache = cache; 269 entry->block = SQUASHFS_INVALID_BLK; 270 entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL); 271 if (entry->data == NULL) { 272 ERROR("Failed to allocate %s cache entry\n", name); 273 goto cleanup; 274 } 275 276 for (j = 0; j < cache->pages; j++) { 277 entry->data[j] = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL); 278 if (entry->data[j] == NULL) { 279 ERROR("Failed to allocate %s buffer\n", name); 280 goto cleanup; 281 } 282 } 283 } 284 285 return cache; 286 287 cleanup: 288 squashfs_cache_delete(cache); 289 return NULL; 290 } 291 292 293 /* 294 * Copy up to length bytes from cache entry to buffer starting at offset bytes 295 * into the cache entry. If there's not length bytes then copy the number of 296 * bytes available. In all cases return the number of bytes copied. 297 */ 298 int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry, 299 int offset, int length) 300 { 301 int remaining = length; 302 303 if (length == 0) 304 return 0; 305 else if (buffer == NULL) 306 return min(length, entry->length - offset); 307 308 while (offset < entry->length) { 309 void *buff = entry->data[offset / PAGE_CACHE_SIZE] 310 + (offset % PAGE_CACHE_SIZE); 311 int bytes = min_t(int, entry->length - offset, 312 PAGE_CACHE_SIZE - (offset % PAGE_CACHE_SIZE)); 313 314 if (bytes >= remaining) { 315 memcpy(buffer, buff, remaining); 316 remaining = 0; 317 break; 318 } 319 320 memcpy(buffer, buff, bytes); 321 buffer += bytes; 322 remaining -= bytes; 323 offset += bytes; 324 } 325 326 return length - remaining; 327 } 328 329 330 /* 331 * Read length bytes from metadata position <block, offset> (block is the 332 * start of the compressed block on disk, and offset is the offset into 333 * the block once decompressed). Data is packed into consecutive blocks, 334 * and length bytes may require reading more than one block. 335 */ 336 int squashfs_read_metadata(struct super_block *sb, void *buffer, 337 u64 *block, int *offset, int length) 338 { 339 struct squashfs_sb_info *msblk = sb->s_fs_info; 340 int bytes, res = length; 341 struct squashfs_cache_entry *entry; 342 343 TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset); 344 345 while (length) { 346 entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0); 347 if (entry->error) { 348 res = entry->error; 349 goto error; 350 } else if (*offset >= entry->length) { 351 res = -EIO; 352 goto error; 353 } 354 355 bytes = squashfs_copy_data(buffer, entry, *offset, length); 356 if (buffer) 357 buffer += bytes; 358 length -= bytes; 359 *offset += bytes; 360 361 if (*offset == entry->length) { 362 *block = entry->next_index; 363 *offset = 0; 364 } 365 366 squashfs_cache_put(entry); 367 } 368 369 return res; 370 371 error: 372 squashfs_cache_put(entry); 373 return res; 374 } 375 376 377 /* 378 * Look-up in the fragmment cache the fragment located at <start_block> in the 379 * filesystem. If necessary read and decompress it from disk. 380 */ 381 struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb, 382 u64 start_block, int length) 383 { 384 struct squashfs_sb_info *msblk = sb->s_fs_info; 385 386 return squashfs_cache_get(sb, msblk->fragment_cache, start_block, 387 length); 388 } 389 390 391 /* 392 * Read and decompress the datablock located at <start_block> in the 393 * filesystem. The cache is used here to avoid duplicating locking and 394 * read/decompress code. 395 */ 396 struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb, 397 u64 start_block, int length) 398 { 399 struct squashfs_sb_info *msblk = sb->s_fs_info; 400 401 return squashfs_cache_get(sb, msblk->read_page, start_block, length); 402 } 403 404 405 /* 406 * Read a filesystem table (uncompressed sequence of bytes) from disk 407 */ 408 void *squashfs_read_table(struct super_block *sb, u64 block, int length) 409 { 410 int pages = (length + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT; 411 int i, res; 412 void *table, *buffer, **data; 413 414 table = buffer = kmalloc(length, GFP_KERNEL); 415 if (table == NULL) 416 return ERR_PTR(-ENOMEM); 417 418 data = kcalloc(pages, sizeof(void *), GFP_KERNEL); 419 if (data == NULL) { 420 res = -ENOMEM; 421 goto failed; 422 } 423 424 for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE) 425 data[i] = buffer; 426 427 res = squashfs_read_data(sb, data, block, length | 428 SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, length, pages); 429 430 kfree(data); 431 432 if (res < 0) 433 goto failed; 434 435 return table; 436 437 failed: 438 kfree(table); 439 return ERR_PTR(res); 440 } 441