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 = kzalloc(sizeof(*cache), GFP_KERNEL); 228 229 if (cache == NULL) { 230 ERROR("Failed to allocate %s cache\n", name); 231 return NULL; 232 } 233 234 cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL); 235 if (cache->entry == NULL) { 236 ERROR("Failed to allocate %s cache\n", name); 237 goto cleanup; 238 } 239 240 cache->curr_blk = 0; 241 cache->next_blk = 0; 242 cache->unused = entries; 243 cache->entries = entries; 244 cache->block_size = block_size; 245 cache->pages = block_size >> PAGE_SHIFT; 246 cache->pages = cache->pages ? cache->pages : 1; 247 cache->name = name; 248 cache->num_waiters = 0; 249 spin_lock_init(&cache->lock); 250 init_waitqueue_head(&cache->wait_queue); 251 252 for (i = 0; i < entries; i++) { 253 struct squashfs_cache_entry *entry = &cache->entry[i]; 254 255 init_waitqueue_head(&cache->entry[i].wait_queue); 256 entry->cache = cache; 257 entry->block = SQUASHFS_INVALID_BLK; 258 entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL); 259 if (entry->data == NULL) { 260 ERROR("Failed to allocate %s cache entry\n", name); 261 goto cleanup; 262 } 263 264 for (j = 0; j < cache->pages; j++) { 265 entry->data[j] = kmalloc(PAGE_SIZE, GFP_KERNEL); 266 if (entry->data[j] == NULL) { 267 ERROR("Failed to allocate %s buffer\n", name); 268 goto cleanup; 269 } 270 } 271 272 entry->actor = squashfs_page_actor_init(entry->data, 273 cache->pages, 0); 274 if (entry->actor == NULL) { 275 ERROR("Failed to allocate %s cache entry\n", name); 276 goto cleanup; 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_SIZE] 305 + (offset % PAGE_SIZE); 306 int bytes = min_t(int, entry->length - offset, 307 PAGE_SIZE - (offset % PAGE_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, res = length; 336 struct squashfs_cache_entry *entry; 337 338 TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset); 339 340 if (unlikely(length < 0)) 341 return -EIO; 342 343 while (length) { 344 entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0); 345 if (entry->error) { 346 res = entry->error; 347 goto error; 348 } else if (*offset >= entry->length) { 349 res = -EIO; 350 goto error; 351 } 352 353 bytes = squashfs_copy_data(buffer, entry, *offset, length); 354 if (buffer) 355 buffer += bytes; 356 length -= bytes; 357 *offset += bytes; 358 359 if (*offset == entry->length) { 360 *block = entry->next_index; 361 *offset = 0; 362 } 363 364 squashfs_cache_put(entry); 365 } 366 367 return res; 368 369 error: 370 squashfs_cache_put(entry); 371 return res; 372 } 373 374 375 /* 376 * Look-up in the fragmment cache the fragment located at <start_block> in the 377 * filesystem. If necessary read and decompress it from disk. 378 */ 379 struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb, 380 u64 start_block, int length) 381 { 382 struct squashfs_sb_info *msblk = sb->s_fs_info; 383 384 return squashfs_cache_get(sb, msblk->fragment_cache, start_block, 385 length); 386 } 387 388 389 /* 390 * Read and decompress the datablock located at <start_block> in the 391 * filesystem. The cache is used here to avoid duplicating locking and 392 * read/decompress code. 393 */ 394 struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb, 395 u64 start_block, int length) 396 { 397 struct squashfs_sb_info *msblk = sb->s_fs_info; 398 399 return squashfs_cache_get(sb, msblk->read_page, start_block, length); 400 } 401 402 403 /* 404 * Read a filesystem table (uncompressed sequence of bytes) from disk 405 */ 406 void *squashfs_read_table(struct super_block *sb, u64 block, int length) 407 { 408 int pages = (length + PAGE_SIZE - 1) >> PAGE_SHIFT; 409 int i, res; 410 void *table, *buffer, **data; 411 struct squashfs_page_actor *actor; 412 413 table = buffer = kmalloc(length, GFP_KERNEL); 414 if (table == NULL) 415 return ERR_PTR(-ENOMEM); 416 417 data = kcalloc(pages, sizeof(void *), GFP_KERNEL); 418 if (data == NULL) { 419 res = -ENOMEM; 420 goto failed; 421 } 422 423 actor = squashfs_page_actor_init(data, pages, length); 424 if (actor == NULL) { 425 res = -ENOMEM; 426 goto failed2; 427 } 428 429 for (i = 0; i < pages; i++, buffer += PAGE_SIZE) 430 data[i] = buffer; 431 432 res = squashfs_read_data(sb, block, length | 433 SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, actor); 434 435 kfree(data); 436 kfree(actor); 437 438 if (res < 0) 439 goto failed; 440 441 return table; 442 443 failed2: 444 kfree(data); 445 failed: 446 kfree(table); 447 return ERR_PTR(res); 448 } 449