1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * Squashfs - a compressed read only filesystem for Linux 4 * 5 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008 6 * Phillip Lougher <phillip@squashfs.org.uk> 7 * 8 * cache.c 9 */ 10 11 /* 12 * Blocks in Squashfs are compressed. To avoid repeatedly decompressing 13 * recently accessed data Squashfs uses two small metadata and fragment caches. 14 * 15 * This file implements a generic cache implementation used for both caches, 16 * plus functions layered ontop of the generic cache implementation to 17 * access the metadata and fragment caches. 18 * 19 * To avoid out of memory and fragmentation issues with vmalloc the cache 20 * uses sequences of kmalloced PAGE_SIZE buffers. 21 * 22 * It should be noted that the cache is not used for file datablocks, these 23 * are decompressed and cached in the page-cache in the normal way. The 24 * cache is only used to temporarily cache fragment and metadata blocks 25 * which have been read as as a result of a metadata (i.e. inode or 26 * directory) or fragment access. Because metadata and fragments are packed 27 * together into blocks (to gain greater compression) the read of a particular 28 * piece of metadata or fragment will retrieve other metadata/fragments which 29 * have been packed with it, these because of locality-of-reference may be read 30 * in the near future. Temporarily caching them ensures they are available for 31 * near future access without requiring an additional read and decompress. 32 */ 33 34 #include <linux/fs.h> 35 #include <linux/vfs.h> 36 #include <linux/slab.h> 37 #include <linux/vmalloc.h> 38 #include <linux/sched.h> 39 #include <linux/spinlock.h> 40 #include <linux/wait.h> 41 #include <linux/pagemap.h> 42 43 #include "squashfs_fs.h" 44 #include "squashfs_fs_sb.h" 45 #include "squashfs.h" 46 #include "page_actor.h" 47 48 /* 49 * Look-up block in cache, and increment usage count. If not in cache, read 50 * and decompress it from disk. 51 */ 52 struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb, 53 struct squashfs_cache *cache, u64 block, int length) 54 { 55 int i, n; 56 struct squashfs_cache_entry *entry; 57 58 spin_lock(&cache->lock); 59 60 while (1) { 61 for (i = cache->curr_blk, n = 0; n < cache->entries; n++) { 62 if (cache->entry[i].block == block) { 63 cache->curr_blk = i; 64 break; 65 } 66 i = (i + 1) % cache->entries; 67 } 68 69 if (n == cache->entries) { 70 /* 71 * Block not in cache, if all cache entries are used 72 * go to sleep waiting for one to become available. 73 */ 74 if (cache->unused == 0) { 75 cache->num_waiters++; 76 spin_unlock(&cache->lock); 77 wait_event(cache->wait_queue, cache->unused); 78 spin_lock(&cache->lock); 79 cache->num_waiters--; 80 continue; 81 } 82 83 /* 84 * At least one unused cache entry. A simple 85 * round-robin strategy is used to choose the entry to 86 * be evicted from the cache. 87 */ 88 i = cache->next_blk; 89 for (n = 0; n < cache->entries; n++) { 90 if (cache->entry[i].refcount == 0) 91 break; 92 i = (i + 1) % cache->entries; 93 } 94 95 cache->next_blk = (i + 1) % cache->entries; 96 entry = &cache->entry[i]; 97 98 /* 99 * Initialise chosen cache entry, and fill it in from 100 * disk. 101 */ 102 cache->unused--; 103 entry->block = block; 104 entry->refcount = 1; 105 entry->pending = 1; 106 entry->num_waiters = 0; 107 entry->error = 0; 108 spin_unlock(&cache->lock); 109 110 entry->length = squashfs_read_data(sb, block, length, 111 &entry->next_index, entry->actor); 112 113 spin_lock(&cache->lock); 114 115 if (entry->length < 0) 116 entry->error = entry->length; 117 118 entry->pending = 0; 119 120 /* 121 * While filling this entry one or more other processes 122 * have looked it up in the cache, and have slept 123 * waiting for it to become available. 124 */ 125 if (entry->num_waiters) { 126 spin_unlock(&cache->lock); 127 wake_up_all(&entry->wait_queue); 128 } else 129 spin_unlock(&cache->lock); 130 131 goto out; 132 } 133 134 /* 135 * Block already in cache. Increment refcount so it doesn't 136 * get reused until we're finished with it, if it was 137 * previously unused there's one less cache entry available 138 * for reuse. 139 */ 140 entry = &cache->entry[i]; 141 if (entry->refcount == 0) 142 cache->unused--; 143 entry->refcount++; 144 145 /* 146 * If the entry is currently being filled in by another process 147 * go to sleep waiting for it to become available. 148 */ 149 if (entry->pending) { 150 entry->num_waiters++; 151 spin_unlock(&cache->lock); 152 wait_event(entry->wait_queue, !entry->pending); 153 } else 154 spin_unlock(&cache->lock); 155 156 goto out; 157 } 158 159 out: 160 TRACE("Got %s %d, start block %lld, refcount %d, error %d\n", 161 cache->name, i, entry->block, entry->refcount, entry->error); 162 163 if (entry->error) 164 ERROR("Unable to read %s cache entry [%llx]\n", cache->name, 165 block); 166 return entry; 167 } 168 169 170 /* 171 * Release cache entry, once usage count is zero it can be reused. 172 */ 173 void squashfs_cache_put(struct squashfs_cache_entry *entry) 174 { 175 struct squashfs_cache *cache = entry->cache; 176 177 spin_lock(&cache->lock); 178 entry->refcount--; 179 if (entry->refcount == 0) { 180 cache->unused++; 181 /* 182 * If there's any processes waiting for a block to become 183 * available, wake one up. 184 */ 185 if (cache->num_waiters) { 186 spin_unlock(&cache->lock); 187 wake_up(&cache->wait_queue); 188 return; 189 } 190 } 191 spin_unlock(&cache->lock); 192 } 193 194 /* 195 * Delete cache reclaiming all kmalloced buffers. 196 */ 197 void squashfs_cache_delete(struct squashfs_cache *cache) 198 { 199 int i, j; 200 201 if (cache == NULL) 202 return; 203 204 for (i = 0; i < cache->entries; i++) { 205 if (cache->entry[i].data) { 206 for (j = 0; j < cache->pages; j++) 207 kfree(cache->entry[i].data[j]); 208 kfree(cache->entry[i].data); 209 } 210 kfree(cache->entry[i].actor); 211 } 212 213 kfree(cache->entry); 214 kfree(cache); 215 } 216 217 218 /* 219 * Initialise cache allocating the specified number of entries, each of 220 * size block_size. To avoid vmalloc fragmentation issues each entry 221 * is allocated as a sequence of kmalloced PAGE_SIZE buffers. 222 */ 223 struct squashfs_cache *squashfs_cache_init(char *name, int entries, 224 int block_size) 225 { 226 int i, j; 227 struct squashfs_cache *cache; 228 229 if (entries == 0) 230 return NULL; 231 232 cache = kzalloc(sizeof(*cache), GFP_KERNEL); 233 if (cache == NULL) { 234 ERROR("Failed to allocate %s cache\n", name); 235 return ERR_PTR(-ENOMEM); 236 } 237 238 cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL); 239 if (cache->entry == NULL) { 240 ERROR("Failed to allocate %s cache\n", name); 241 goto cleanup; 242 } 243 244 cache->curr_blk = 0; 245 cache->next_blk = 0; 246 cache->unused = entries; 247 cache->entries = entries; 248 cache->block_size = block_size; 249 cache->pages = block_size >> PAGE_SHIFT; 250 cache->pages = cache->pages ? cache->pages : 1; 251 cache->name = name; 252 cache->num_waiters = 0; 253 spin_lock_init(&cache->lock); 254 init_waitqueue_head(&cache->wait_queue); 255 256 for (i = 0; i < entries; i++) { 257 struct squashfs_cache_entry *entry = &cache->entry[i]; 258 259 init_waitqueue_head(&cache->entry[i].wait_queue); 260 entry->cache = cache; 261 entry->block = SQUASHFS_INVALID_BLK; 262 entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL); 263 if (entry->data == NULL) { 264 ERROR("Failed to allocate %s cache entry\n", name); 265 goto cleanup; 266 } 267 268 for (j = 0; j < cache->pages; j++) { 269 entry->data[j] = kmalloc(PAGE_SIZE, GFP_KERNEL); 270 if (entry->data[j] == NULL) { 271 ERROR("Failed to allocate %s buffer\n", name); 272 goto cleanup; 273 } 274 } 275 276 entry->actor = squashfs_page_actor_init(entry->data, 277 cache->pages, 0); 278 if (entry->actor == NULL) { 279 ERROR("Failed to allocate %s cache entry\n", name); 280 goto cleanup; 281 } 282 } 283 284 return cache; 285 286 cleanup: 287 squashfs_cache_delete(cache); 288 return ERR_PTR(-ENOMEM); 289 } 290 291 292 /* 293 * Copy up to length bytes from cache entry to buffer starting at offset bytes 294 * into the cache entry. If there's not length bytes then copy the number of 295 * bytes available. In all cases return the number of bytes copied. 296 */ 297 int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry, 298 int offset, int length) 299 { 300 int remaining = length; 301 302 if (length == 0) 303 return 0; 304 else if (buffer == NULL) 305 return min(length, entry->length - offset); 306 307 while (offset < entry->length) { 308 void *buff = entry->data[offset / PAGE_SIZE] 309 + (offset % PAGE_SIZE); 310 int bytes = min_t(int, entry->length - offset, 311 PAGE_SIZE - (offset % PAGE_SIZE)); 312 313 if (bytes >= remaining) { 314 memcpy(buffer, buff, remaining); 315 remaining = 0; 316 break; 317 } 318 319 memcpy(buffer, buff, bytes); 320 buffer += bytes; 321 remaining -= bytes; 322 offset += bytes; 323 } 324 325 return length - remaining; 326 } 327 328 329 /* 330 * Read length bytes from metadata position <block, offset> (block is the 331 * start of the compressed block on disk, and offset is the offset into 332 * the block once decompressed). Data is packed into consecutive blocks, 333 * and length bytes may require reading more than one block. 334 */ 335 int squashfs_read_metadata(struct super_block *sb, void *buffer, 336 u64 *block, int *offset, int length) 337 { 338 struct squashfs_sb_info *msblk = sb->s_fs_info; 339 int bytes, res = length; 340 struct squashfs_cache_entry *entry; 341 342 TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset); 343 344 if (unlikely(length < 0)) 345 return -EIO; 346 347 while (length) { 348 entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0); 349 if (entry->error) { 350 res = entry->error; 351 goto error; 352 } else if (*offset >= entry->length) { 353 res = -EIO; 354 goto error; 355 } 356 357 bytes = squashfs_copy_data(buffer, entry, *offset, length); 358 if (buffer) 359 buffer += bytes; 360 length -= bytes; 361 *offset += bytes; 362 363 if (*offset == entry->length) { 364 *block = entry->next_index; 365 *offset = 0; 366 } 367 368 squashfs_cache_put(entry); 369 } 370 371 return res; 372 373 error: 374 squashfs_cache_put(entry); 375 return res; 376 } 377 378 379 /* 380 * Look-up in the fragmment cache the fragment located at <start_block> in the 381 * filesystem. If necessary read and decompress it from disk. 382 */ 383 struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb, 384 u64 start_block, int length) 385 { 386 struct squashfs_sb_info *msblk = sb->s_fs_info; 387 388 return squashfs_cache_get(sb, msblk->fragment_cache, start_block, 389 length); 390 } 391 392 393 /* 394 * Read and decompress the datablock located at <start_block> in the 395 * filesystem. The cache is used here to avoid duplicating locking and 396 * read/decompress code. 397 */ 398 struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb, 399 u64 start_block, int length) 400 { 401 struct squashfs_sb_info *msblk = sb->s_fs_info; 402 403 return squashfs_cache_get(sb, msblk->read_page, start_block, length); 404 } 405 406 407 /* 408 * Read a filesystem table (uncompressed sequence of bytes) from disk 409 */ 410 void *squashfs_read_table(struct super_block *sb, u64 block, int length) 411 { 412 int pages = (length + PAGE_SIZE - 1) >> PAGE_SHIFT; 413 int i, res; 414 void *table, *buffer, **data; 415 struct squashfs_page_actor *actor; 416 417 table = buffer = kmalloc(length, GFP_KERNEL); 418 if (table == NULL) 419 return ERR_PTR(-ENOMEM); 420 421 data = kcalloc(pages, sizeof(void *), GFP_KERNEL); 422 if (data == NULL) { 423 res = -ENOMEM; 424 goto failed; 425 } 426 427 actor = squashfs_page_actor_init(data, pages, length); 428 if (actor == NULL) { 429 res = -ENOMEM; 430 goto failed2; 431 } 432 433 for (i = 0; i < pages; i++, buffer += PAGE_SIZE) 434 data[i] = buffer; 435 436 res = squashfs_read_data(sb, block, length | 437 SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, actor); 438 439 kfree(data); 440 kfree(actor); 441 442 if (res < 0) 443 goto failed; 444 445 return table; 446 447 failed2: 448 kfree(data); 449 failed: 450 kfree(table); 451 return ERR_PTR(res); 452 } 453