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 (at) 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/zlib.h> 55 #include <linux/pagemap.h> 56 57 #include "squashfs_fs.h" 58 #include "squashfs_fs_sb.h" 59 #include "squashfs_fs_i.h" 60 #include "squashfs.h" 61 62 /* 63 * Look-up block in cache, and increment usage count. If not in cache, read 64 * and decompress it from disk. 65 */ 66 struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb, 67 struct squashfs_cache *cache, u64 block, int length) 68 { 69 int i, n; 70 struct squashfs_cache_entry *entry; 71 72 spin_lock(&cache->lock); 73 74 while (1) { 75 for (i = 0; i < cache->entries; i++) 76 if (cache->entry[i].block == block) 77 break; 78 79 if (i == cache->entries) { 80 /* 81 * Block not in cache, if all cache entries are used 82 * go to sleep waiting for one to become available. 83 */ 84 if (cache->unused == 0) { 85 cache->num_waiters++; 86 spin_unlock(&cache->lock); 87 wait_event(cache->wait_queue, cache->unused); 88 spin_lock(&cache->lock); 89 cache->num_waiters--; 90 continue; 91 } 92 93 /* 94 * At least one unused cache entry. A simple 95 * round-robin strategy is used to choose the entry to 96 * be evicted from the cache. 97 */ 98 i = cache->next_blk; 99 for (n = 0; n < cache->entries; n++) { 100 if (cache->entry[i].refcount == 0) 101 break; 102 i = (i + 1) % cache->entries; 103 } 104 105 cache->next_blk = (i + 1) % cache->entries; 106 entry = &cache->entry[i]; 107 108 /* 109 * Initialise choosen cache entry, and fill it in from 110 * disk. 111 */ 112 cache->unused--; 113 entry->block = block; 114 entry->refcount = 1; 115 entry->pending = 1; 116 entry->num_waiters = 0; 117 entry->error = 0; 118 spin_unlock(&cache->lock); 119 120 entry->length = squashfs_read_data(sb, entry->data, 121 block, length, &entry->next_index, 122 cache->block_size); 123 124 spin_lock(&cache->lock); 125 126 if (entry->length < 0) 127 entry->error = entry->length; 128 129 entry->pending = 0; 130 131 /* 132 * While filling this entry one or more other processes 133 * have looked it up in the cache, and have slept 134 * waiting for it to become available. 135 */ 136 if (entry->num_waiters) { 137 spin_unlock(&cache->lock); 138 wake_up_all(&entry->wait_queue); 139 } else 140 spin_unlock(&cache->lock); 141 142 goto out; 143 } 144 145 /* 146 * Block already in cache. Increment refcount so it doesn't 147 * get reused until we're finished with it, if it was 148 * previously unused there's one less cache entry available 149 * for reuse. 150 */ 151 entry = &cache->entry[i]; 152 if (entry->refcount == 0) 153 cache->unused--; 154 entry->refcount++; 155 156 /* 157 * If the entry is currently being filled in by another process 158 * go to sleep waiting for it to become available. 159 */ 160 if (entry->pending) { 161 entry->num_waiters++; 162 spin_unlock(&cache->lock); 163 wait_event(entry->wait_queue, !entry->pending); 164 } else 165 spin_unlock(&cache->lock); 166 167 goto out; 168 } 169 170 out: 171 TRACE("Got %s %d, start block %lld, refcount %d, error %d\n", 172 cache->name, i, entry->block, entry->refcount, entry->error); 173 174 if (entry->error) 175 ERROR("Unable to read %s cache entry [%llx]\n", cache->name, 176 block); 177 return entry; 178 } 179 180 181 /* 182 * Release cache entry, once usage count is zero it can be reused. 183 */ 184 void squashfs_cache_put(struct squashfs_cache_entry *entry) 185 { 186 struct squashfs_cache *cache = entry->cache; 187 188 spin_lock(&cache->lock); 189 entry->refcount--; 190 if (entry->refcount == 0) { 191 cache->unused++; 192 /* 193 * If there's any processes waiting for a block to become 194 * available, wake one up. 195 */ 196 if (cache->num_waiters) { 197 spin_unlock(&cache->lock); 198 wake_up(&cache->wait_queue); 199 return; 200 } 201 } 202 spin_unlock(&cache->lock); 203 } 204 205 /* 206 * Delete cache reclaiming all kmalloced buffers. 207 */ 208 void squashfs_cache_delete(struct squashfs_cache *cache) 209 { 210 int i, j; 211 212 if (cache == NULL) 213 return; 214 215 for (i = 0; i < cache->entries; i++) { 216 if (cache->entry[i].data) { 217 for (j = 0; j < cache->pages; j++) 218 kfree(cache->entry[i].data[j]); 219 kfree(cache->entry[i].data); 220 } 221 } 222 223 kfree(cache->entry); 224 kfree(cache); 225 } 226 227 228 /* 229 * Initialise cache allocating the specified number of entries, each of 230 * size block_size. To avoid vmalloc fragmentation issues each entry 231 * is allocated as a sequence of kmalloced PAGE_CACHE_SIZE buffers. 232 */ 233 struct squashfs_cache *squashfs_cache_init(char *name, int entries, 234 int block_size) 235 { 236 int i, j; 237 struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL); 238 239 if (cache == NULL) { 240 ERROR("Failed to allocate %s cache\n", name); 241 return NULL; 242 } 243 244 cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL); 245 if (cache->entry == NULL) { 246 ERROR("Failed to allocate %s cache\n", name); 247 goto cleanup; 248 } 249 250 cache->next_blk = 0; 251 cache->unused = entries; 252 cache->entries = entries; 253 cache->block_size = block_size; 254 cache->pages = block_size >> PAGE_CACHE_SHIFT; 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); 410 kfree(data); 411 return res; 412 } 413
