fs/mbcache.c

   1 /*
   2  * linux/fs/mbcache.c
   3  * (C) 2001-2002 Andreas Gruenbacher, <a.gruenbacher@computer.org>
   4  */
   5
   6 /*
   7  * Filesystem Meta Information Block Cache (mbcache)
   8  *
   9  * The mbcache caches blocks of block devices that need to be located
  10  * by their device/block number, as well as by other criteria (such
  11  * as the block's contents).
  12  *
  13  * There can only be one cache entry in a cache per device and block number.
  14  * Additional indexes need not be unique in this sense. The number of
  15  * additional indexes (=other criteria) can be hardwired at compile time
  16  * or specified at cache create time.
  17  *
  18  * Each cache entry is of fixed size. An entry may be `valid' or `invalid'
  19  * in the cache. A valid entry is in the main hash tables of the cache,
  20  * and may also be in the lru list. An invalid entry is not in any hashes
  21  * or lists.
  22  *
  23  * A valid cache entry is only in the lru list if no handles refer to it.
  24  * Invalid cache entries will be freed when the last handle to the cache
  25  * entry is released. Entries that cannot be freed immediately are put
  26  * back on the lru list.
  27  */
  28
  29 #include <linux/kernel.h>
  30 #include <linux/module.h>
  31
  32 #include <linux/hash.h>
  33 #include <linux/fs.h>
  34 #include <linux/mm.h>
  35 #include <linux/slab.h>
  36 #include <linux/sched.h>
  37 #include <linux/list_bl.h>
  38 #include <linux/mbcache.h>
  39 #include <linux/init.h>
  40
  41 #ifdef MB_CACHE_DEBUG
  42 # define mb_debug(f...) do { \
  43                 printk(KERN_DEBUG f); \
  44                 printk("\n"); \
  45         } while (0)
  46 #define mb_assert(c) do { if (!(c)) \
  47                 printk(KERN_ERR "assertion " #c " failed\n"); \
  48         } while(0)
  49 #else
  50 # define mb_debug(f...) do { } while(0)
  51 # define mb_assert(c) do { } while(0)
  52 #endif
  53 #define mb_error(f...) do { \
  54                 printk(KERN_ERR f); \
  55                 printk("\n"); \
  56         } while(0)
  57
  58 #define MB_CACHE_WRITER ((unsigned short)~0U >> 1)
  59
  60 static DECLARE_WAIT_QUEUE_HEAD(mb_cache_queue);
  61
  62 MODULE_AUTHOR("Andreas Gruenbacher <a.gruenbacher@computer.org>");
  63 MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
  64 MODULE_LICENSE("GPL");
  65
  66 EXPORT_SYMBOL(mb_cache_create);
  67 EXPORT_SYMBOL(mb_cache_shrink);
  68 EXPORT_SYMBOL(mb_cache_destroy);
  69 EXPORT_SYMBOL(mb_cache_entry_alloc);
  70 EXPORT_SYMBOL(mb_cache_entry_insert);
  71 EXPORT_SYMBOL(mb_cache_entry_release);
  72 EXPORT_SYMBOL(mb_cache_entry_free);
  73 EXPORT_SYMBOL(mb_cache_entry_get);
  74 #if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0)
  75 EXPORT_SYMBOL(mb_cache_entry_find_first);
  76 EXPORT_SYMBOL(mb_cache_entry_find_next);
  77 #endif
  78
  79 /*
  80  * Global data: list of all mbcache's, lru list, and a spinlock for
  81  * accessing cache data structures on SMP machines. The lru list is
  82  * global across all mbcaches.
  83  */
  84
  85 static LIST_HEAD(mb_cache_list);
  86 static LIST_HEAD(mb_cache_lru_list);
  87 static DEFINE_SPINLOCK(mb_cache_spinlock);
  88
  89 static inline int
  90 __mb_cache_entry_is_block_hashed(struct mb_cache_entry *ce)
  91 {
  92         return !hlist_bl_unhashed(&ce->e_block_list);
  93 }
  94
  95
  96 static inline void
  97 __mb_cache_entry_unhash_block(struct mb_cache_entry *ce)
  98 {
  99         if (__mb_cache_entry_is_block_hashed(ce))
 100                 hlist_bl_del_init(&ce->e_block_list);
 101 }
 102
 103 static inline int
 104 __mb_cache_entry_is_index_hashed(struct mb_cache_entry *ce)
 105 {
 106         return !hlist_bl_unhashed(&ce->e_index.o_list);
 107 }
 108
 109 static inline void
 110 __mb_cache_entry_unhash_index(struct mb_cache_entry *ce)
 111 {
 112         if (__mb_cache_entry_is_index_hashed(ce))
 113                 hlist_bl_del_init(&ce->e_index.o_list);
 114 }
 115
 116 static inline void
 117 __mb_cache_entry_unhash(struct mb_cache_entry *ce)
 118 {
 119         __mb_cache_entry_unhash_index(ce);
 120         __mb_cache_entry_unhash_block(ce);
 121 }
 122
 123 static void
 124 __mb_cache_entry_forget(struct mb_cache_entry *ce, gfp_t gfp_mask)
 125 {
 126         struct mb_cache *cache = ce->e_cache;
 127
 128         mb_assert(!(ce->e_used || ce->e_queued));
 129         kmem_cache_free(cache->c_entry_cache, ce);
 130         atomic_dec(&cache->c_entry_count);
 131 }
 132
 133
 134 static void
 135 __mb_cache_entry_release_unlock(struct mb_cache_entry *ce)
 136         __releases(mb_cache_spinlock)
 137 {
 138         /* Wake up all processes queuing for this cache entry. */
 139         if (ce->e_queued)
 140                 wake_up_all(&mb_cache_queue);
 141         if (ce->e_used >= MB_CACHE_WRITER)
 142                 ce->e_used -= MB_CACHE_WRITER;
 143         ce->e_used--;
 144         if (!(ce->e_used || ce->e_queued)) {
 145                 if (!__mb_cache_entry_is_block_hashed(ce))
 146                         goto forget;
 147                 mb_assert(list_empty(&ce->e_lru_list));
 148                 list_add_tail(&ce->e_lru_list, &mb_cache_lru_list);
 149         }
 150         spin_unlock(&mb_cache_spinlock);
 151         return;
 152 forget:
 153         spin_unlock(&mb_cache_spinlock);
 154         __mb_cache_entry_forget(ce, GFP_KERNEL);
 155 }
 156
 157
 158 /*
 159  * mb_cache_shrink_scan()  memory pressure callback
 160  *
 161  * This function is called by the kernel memory management when memory
 162  * gets low.
 163  *
 164  * @shrink: (ignored)
 165  * @sc: shrink_control passed from reclaim
 166  *
 167  * Returns the number of objects freed.
 168  */
 169 static unsigned long
 170 mb_cache_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 171 {
 172         LIST_HEAD(free_list);
 173         struct mb_cache_entry *entry, *tmp;
 174         int nr_to_scan = sc->nr_to_scan;
 175         gfp_t gfp_mask = sc->gfp_mask;
 176         unsigned long freed = 0;
 177
 178         mb_debug("trying to free %d entries", nr_to_scan);
 179         spin_lock(&mb_cache_spinlock);
 180         while (nr_to_scan-- && !list_empty(&mb_cache_lru_list)) {
 181                 struct mb_cache_entry *ce =
 182                         list_entry(mb_cache_lru_list.next,
 183                                    struct mb_cache_entry, e_lru_list);
 184                 list_move_tail(&ce->e_lru_list, &free_list);
 185                 __mb_cache_entry_unhash(ce);
 186                 freed++;
 187         }
 188         spin_unlock(&mb_cache_spinlock);
 189         list_for_each_entry_safe(entry, tmp, &free_list, e_lru_list) {
 190                 __mb_cache_entry_forget(entry, gfp_mask);
 191         }
 192         return freed;
 193 }
 194
 195 static unsigned long
 196 mb_cache_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
 197 {
 198         struct mb_cache *cache;
 199         unsigned long count = 0;
 200
 201         spin_lock(&mb_cache_spinlock);
 202         list_for_each_entry(cache, &mb_cache_list, c_cache_list) {
 203                 mb_debug("cache %s (%d)", cache->c_name,
 204                           atomic_read(&cache->c_entry_count));
 205                 count += atomic_read(&cache->c_entry_count);
 206         }
 207         spin_unlock(&mb_cache_spinlock);
 208
 209         return vfs_pressure_ratio(count);
 210 }
 211
 212 static struct shrinker mb_cache_shrinker = {
 213         .count_objects = mb_cache_shrink_count,
 214         .scan_objects = mb_cache_shrink_scan,
 215         .seeks = DEFAULT_SEEKS,
 216 };
 217
 218 /*
 219  * mb_cache_create()  create a new cache
 220  *
 221  * All entries in one cache are equal size. Cache entries may be from
 222  * multiple devices. If this is the first mbcache created, registers
 223  * the cache with kernel memory management. Returns NULL if no more
 224  * memory was available.
 225  *
 226  * @name: name of the cache (informal)
 227  * @bucket_bits: log2(number of hash buckets)
 228  */
 229 struct mb_cache *
 230 mb_cache_create(const char *name, int bucket_bits)
 231 {
 232         int n, bucket_count = 1 << bucket_bits;
 233         struct mb_cache *cache = NULL;
 234
 235         cache = kmalloc(sizeof(struct mb_cache), GFP_KERNEL);
 236         if (!cache)
 237                 return NULL;
 238         cache->c_name = name;
 239         atomic_set(&cache->c_entry_count, 0);
 240         cache->c_bucket_bits = bucket_bits;
 241         cache->c_block_hash = kmalloc(bucket_count *
 242                 sizeof(struct hlist_bl_head), GFP_KERNEL);
 243         if (!cache->c_block_hash)
 244                 goto fail;
 245         for (n=0; n<bucket_count; n++)
 246                 INIT_HLIST_BL_HEAD(&cache->c_block_hash[n]);
 247         cache->c_index_hash = kmalloc(bucket_count *
 248                 sizeof(struct hlist_bl_head), GFP_KERNEL);
 249         if (!cache->c_index_hash)
 250                 goto fail;
 251         for (n=0; n<bucket_count; n++)
 252                 INIT_HLIST_BL_HEAD(&cache->c_index_hash[n]);
 253         cache->c_entry_cache = kmem_cache_create(name,
 254                 sizeof(struct mb_cache_entry), 0,
 255                 SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
 256         if (!cache->c_entry_cache)
 257                 goto fail2;
 258
 259         /*
 260          * Set an upper limit on the number of cache entries so that the hash
 261          * chains won't grow too long.
 262          */
 263         cache->c_max_entries = bucket_count << 4;
 264
 265         spin_lock(&mb_cache_spinlock);
 266         list_add(&cache->c_cache_list, &mb_cache_list);
 267         spin_unlock(&mb_cache_spinlock);
 268         return cache;
 269
 270 fail2:
 271         kfree(cache->c_index_hash);
 272
 273 fail:
 274         kfree(cache->c_block_hash);
 275         kfree(cache);
 276         return NULL;
 277 }
 278
 279
 280 /*
 281  * mb_cache_shrink()
 282  *
 283  * Removes all cache entries of a device from the cache. All cache entries
 284  * currently in use cannot be freed, and thus remain in the cache. All others
 285  * are freed.
 286  *
 287  * @bdev: which device's cache entries to shrink
 288  */
 289 void
 290 mb_cache_shrink(struct block_device *bdev)
 291 {
 292         LIST_HEAD(free_list);
 293         struct list_head *l, *ltmp;
 294
 295         spin_lock(&mb_cache_spinlock);
 296         list_for_each_safe(l, ltmp, &mb_cache_lru_list) {
 297                 struct mb_cache_entry *ce =
 298                         list_entry(l, struct mb_cache_entry, e_lru_list);
 299                 if (ce->e_bdev == bdev) {
 300                         list_move_tail(&ce->e_lru_list, &free_list);
 301                         __mb_cache_entry_unhash(ce);
 302                 }
 303         }
 304         spin_unlock(&mb_cache_spinlock);
 305         list_for_each_safe(l, ltmp, &free_list) {
 306                 __mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
 307                                                    e_lru_list), GFP_KERNEL);
 308         }
 309 }
 310
 311
 312 /*
 313  * mb_cache_destroy()
 314  *
 315  * Shrinks the cache to its minimum possible size (hopefully 0 entries),
 316  * and then destroys it. If this was the last mbcache, un-registers the
 317  * mbcache from kernel memory management.
 318  */
 319 void
 320 mb_cache_destroy(struct mb_cache *cache)
 321 {
 322         LIST_HEAD(free_list);
 323         struct list_head *l, *ltmp;
 324
 325         spin_lock(&mb_cache_spinlock);
 326         list_for_each_safe(l, ltmp, &mb_cache_lru_list) {
 327                 struct mb_cache_entry *ce =
 328                         list_entry(l, struct mb_cache_entry, e_lru_list);
 329                 if (ce->e_cache == cache) {
 330                         list_move_tail(&ce->e_lru_list, &free_list);
 331                         __mb_cache_entry_unhash(ce);
 332                 }
 333         }
 334         list_del(&cache->c_cache_list);
 335         spin_unlock(&mb_cache_spinlock);
 336
 337         list_for_each_safe(l, ltmp, &free_list) {
 338                 __mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
 339                                                    e_lru_list), GFP_KERNEL);
 340         }
 341
 342         if (atomic_read(&cache->c_entry_count) > 0) {
 343                 mb_error("cache %s: %d orphaned entries",
 344                           cache->c_name,
 345                           atomic_read(&cache->c_entry_count));
 346         }
 347
 348         kmem_cache_destroy(cache->c_entry_cache);
 349
 350         kfree(cache->c_index_hash);
 351         kfree(cache->c_block_hash);
 352         kfree(cache);
 353 }
 354
 355 /*
 356  * mb_cache_entry_alloc()
 357  *
 358  * Allocates a new cache entry. The new entry will not be valid initially,
 359  * and thus cannot be looked up yet. It should be filled with data, and
 360  * then inserted into the cache using mb_cache_entry_insert(). Returns NULL
 361  * if no more memory was available.
 362  */
 363 struct mb_cache_entry *
 364 mb_cache_entry_alloc(struct mb_cache *cache, gfp_t gfp_flags)
 365 {
 366         struct mb_cache_entry *ce = NULL;
 367
 368         if (atomic_read(&cache->c_entry_count) >= cache->c_max_entries) {
 369                 spin_lock(&mb_cache_spinlock);
 370                 if (!list_empty(&mb_cache_lru_list)) {
 371                         ce = list_entry(mb_cache_lru_list.next,
 372                                         struct mb_cache_entry, e_lru_list);
 373                         list_del_init(&ce->e_lru_list);
 374                         __mb_cache_entry_unhash(ce);
 375                 }
 376                 spin_unlock(&mb_cache_spinlock);
 377         }
 378         if (!ce) {
 379                 ce = kmem_cache_alloc(cache->c_entry_cache, gfp_flags);
 380                 if (!ce)
 381                         return NULL;
 382                 atomic_inc(&cache->c_entry_count);
 383                 INIT_LIST_HEAD(&ce->e_lru_list);
 384                 INIT_HLIST_BL_NODE(&ce->e_block_list);
 385                 INIT_HLIST_BL_NODE(&ce->e_index.o_list);
 386                 ce->e_cache = cache;
 387                 ce->e_queued = 0;
 388         }
 389         ce->e_block_hash_p = &cache->c_block_hash[0];
 390         ce->e_index_hash_p = &cache->c_index_hash[0];
 391         ce->e_used = 1 + MB_CACHE_WRITER;
 392         return ce;
 393 }
 394
 395
 396 /*
 397  * mb_cache_entry_insert()
 398  *
 399  * Inserts an entry that was allocated using mb_cache_entry_alloc() into
 400  * the cache. After this, the cache entry can be looked up, but is not yet
 401  * in the lru list as the caller still holds a handle to it. Returns 0 on
 402  * success, or -EBUSY if a cache entry for that device + inode exists
 403  * already (this may happen after a failed lookup, but when another process
 404  * has inserted the same cache entry in the meantime).
 405  *
 406  * @bdev: device the cache entry belongs to
 407  * @block: block number
 408  * @key: lookup key
 409  */
 410 int
 411 mb_cache_entry_insert(struct mb_cache_entry *ce, struct block_device *bdev,
 412                       sector_t block, unsigned int key)
 413 {
 414         struct mb_cache *cache = ce->e_cache;
 415         unsigned int bucket;
 416         struct hlist_bl_node *l;
 417         int error = -EBUSY;
 418         struct hlist_bl_head *block_hash_p;
 419         struct hlist_bl_head *index_hash_p;
 420         struct mb_cache_entry *lce;
 421
 422         mb_assert(ce);
 423         bucket = hash_long((unsigned long)bdev + (block & 0xffffffff),
 424                            cache->c_bucket_bits);
 425         block_hash_p = &cache->c_block_hash[bucket];
 426         spin_lock(&mb_cache_spinlock);
 427         hlist_bl_for_each_entry(lce, l, block_hash_p, e_block_list) {
 428                 if (lce->e_bdev == bdev && lce->e_block == block)
 429                         goto out;
 430         }
 431         mb_assert(!__mb_cache_entry_is_block_hashed(ce));
 432         __mb_cache_entry_unhash(ce);
 433         ce->e_bdev = bdev;
 434         ce->e_block = block;
 435         ce->e_block_hash_p = block_hash_p;
 436         ce->e_index.o_key = key;
 437         bucket = hash_long(key, cache->c_bucket_bits);
 438         index_hash_p = &cache->c_index_hash[bucket];
 439         ce->e_index_hash_p = index_hash_p;
 440         hlist_bl_add_head(&ce->e_index.o_list, index_hash_p);
 441         hlist_bl_add_head(&ce->e_block_list, block_hash_p);
 442         error = 0;
 443 out:
 444         spin_unlock(&mb_cache_spinlock);
 445         return error;
 446 }
 447
 448
 449 /*
 450  * mb_cache_entry_release()
 451  *
 452  * Release a handle to a cache entry. When the last handle to a cache entry
 453  * is released it is either freed (if it is invalid) or otherwise inserted
 454  * in to the lru list.
 455  */
 456 void
 457 mb_cache_entry_release(struct mb_cache_entry *ce)
 458 {
 459         spin_lock(&mb_cache_spinlock);
 460         __mb_cache_entry_release_unlock(ce);
 461 }
 462
 463
 464 /*
 465  * mb_cache_entry_free()
 466  *
 467  * This is equivalent to the sequence mb_cache_entry_takeout() --
 468  * mb_cache_entry_release().
 469  */
 470 void
 471 mb_cache_entry_free(struct mb_cache_entry *ce)
 472 {
 473         spin_lock(&mb_cache_spinlock);
 474         mb_assert(list_empty(&ce->e_lru_list));
 475         __mb_cache_entry_unhash(ce);
 476         __mb_cache_entry_release_unlock(ce);
 477 }
 478
 479
 480 /*
 481  * mb_cache_entry_get()
 482  *
 483  * Get a cache entry  by device / block number. (There can only be one entry
 484  * in the cache per device and block.) Returns NULL if no such cache entry
 485  * exists. The returned cache entry is locked for exclusive access ("single
 486  * writer").
 487  */
 488 struct mb_cache_entry *
 489 mb_cache_entry_get(struct mb_cache *cache, struct block_device *bdev,
 490                    sector_t block)
 491 {
 492         unsigned int bucket;
 493         struct hlist_bl_node *l;
 494         struct mb_cache_entry *ce;
 495         struct hlist_bl_head *block_hash_p;
 496
 497         bucket = hash_long((unsigned long)bdev + (block & 0xffffffff),
 498                            cache->c_bucket_bits);
 499         block_hash_p = &cache->c_block_hash[bucket];
 500         spin_lock(&mb_cache_spinlock);
 501         hlist_bl_for_each_entry(ce, l, block_hash_p, e_block_list) {
 502                 mb_assert(ce->e_block_hash_p == block_hash_p);
 503                 if (ce->e_bdev == bdev && ce->e_block == block) {
 504                         DEFINE_WAIT(wait);
 505
 506                         if (!list_empty(&ce->e_lru_list))
 507                                 list_del_init(&ce->e_lru_list);
 508
 509                         while (ce->e_used > 0) {
 510                                 ce->e_queued++;
 511                                 prepare_to_wait(&mb_cache_queue, &wait,
 512                                                 TASK_UNINTERRUPTIBLE);
 513                                 spin_unlock(&mb_cache_spinlock);
 514                                 schedule();
 515                                 spin_lock(&mb_cache_spinlock);
 516                                 ce->e_queued--;
 517                         }
 518                         finish_wait(&mb_cache_queue, &wait);
 519                         ce->e_used += 1 + MB_CACHE_WRITER;
 520
 521                         if (!__mb_cache_entry_is_block_hashed(ce)) {
 522                                 __mb_cache_entry_release_unlock(ce);
 523                                 return NULL;
 524                         }
 525                         goto cleanup;
 526                 }
 527         }
 528         ce = NULL;
 529
 530 cleanup:
 531         spin_unlock(&mb_cache_spinlock);
 532         return ce;
 533 }
 534
 535 #if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0)
 536
 537 static struct mb_cache_entry *
 538 __mb_cache_entry_find(struct hlist_bl_node *l, struct hlist_bl_head *head,
 539                       struct block_device *bdev, unsigned int key)
 540 {
 541         while (l != NULL) {
 542                 struct mb_cache_entry *ce =
 543                         hlist_bl_entry(l, struct mb_cache_entry,
 544                                 e_index.o_list);
 545                 mb_assert(ce->e_index_hash_p == head);
 546                 if (ce->e_bdev == bdev && ce->e_index.o_key == key) {
 547                         DEFINE_WAIT(wait);
 548
 549                         if (!list_empty(&ce->e_lru_list))
 550                                 list_del_init(&ce->e_lru_list);
 551
 552                         /* Incrementing before holding the lock gives readers
 553                            priority over writers. */
 554                         ce->e_used++;
 555                         while (ce->e_used >= MB_CACHE_WRITER) {
 556                                 ce->e_queued++;
 557                                 prepare_to_wait(&mb_cache_queue, &wait,
 558                                                 TASK_UNINTERRUPTIBLE);
 559                                 spin_unlock(&mb_cache_spinlock);
 560                                 schedule();
 561                                 spin_lock(&mb_cache_spinlock);
 562                                 ce->e_queued--;
 563                         }
 564                         finish_wait(&mb_cache_queue, &wait);
 565
 566                         if (!__mb_cache_entry_is_block_hashed(ce)) {
 567                                 __mb_cache_entry_release_unlock(ce);
 568                                 spin_lock(&mb_cache_spinlock);
 569                                 return ERR_PTR(-EAGAIN);
 570                         }
 571                         return ce;
 572                 }
 573                 l = l->next;
 574         }
 575         return NULL;
 576 }
 577
 578
 579 /*
 580  * mb_cache_entry_find_first()
 581  *
 582  * Find the first cache entry on a given device with a certain key in
 583  * an additional index. Additional matches can be found with
 584  * mb_cache_entry_find_next(). Returns NULL if no match was found. The
 585  * returned cache entry is locked for shared access ("multiple readers").
 586  *
 587  * @cache: the cache to search
 588  * @bdev: the device the cache entry should belong to
 589  * @key: the key in the index
 590  */
 591 struct mb_cache_entry *
 592 mb_cache_entry_find_first(struct mb_cache *cache, struct block_device *bdev,
 593                           unsigned int key)
 594 {
 595         unsigned int bucket = hash_long(key, cache->c_bucket_bits);
 596         struct hlist_bl_node *l;
 597         struct mb_cache_entry *ce = NULL;
 598         struct hlist_bl_head *index_hash_p;
 599
 600         index_hash_p = &cache->c_index_hash[bucket];
 601         spin_lock(&mb_cache_spinlock);
 602         if (!hlist_bl_empty(index_hash_p)) {
 603                 l = hlist_bl_first(index_hash_p);
 604                 ce = __mb_cache_entry_find(l, index_hash_p, bdev, key);
 605         }
 606         spin_unlock(&mb_cache_spinlock);
 607         return ce;
 608 }
 609
 610
 611 /*
 612  * mb_cache_entry_find_next()
 613  *
 614  * Find the next cache entry on a given device with a certain key in an
 615  * additional index. Returns NULL if no match could be found. The previous
 616  * entry is atomatically released, so that mb_cache_entry_find_next() can
 617  * be called like this:
 618  *
 619  * entry = mb_cache_entry_find_first();
 620  * while (entry) {
 621  *      ...
 622  *      entry = mb_cache_entry_find_next(entry, ...);
 623  * }
 624  *
 625  * @prev: The previous match
 626  * @bdev: the device the cache entry should belong to
 627  * @key: the key in the index
 628  */
 629 struct mb_cache_entry *
 630 mb_cache_entry_find_next(struct mb_cache_entry *prev,
 631                          struct block_device *bdev, unsigned int key)
 632 {
 633         struct mb_cache *cache = prev->e_cache;
 634         unsigned int bucket = hash_long(key, cache->c_bucket_bits);
 635         struct hlist_bl_node *l;
 636         struct mb_cache_entry *ce;
 637         struct hlist_bl_head *index_hash_p;
 638
 639         index_hash_p = &cache->c_index_hash[bucket];
 640         mb_assert(prev->e_index_hash_p == index_hash_p);
 641         spin_lock(&mb_cache_spinlock);
 642         mb_assert(!hlist_bl_empty(index_hash_p));
 643         l = prev->e_index.o_list.next;
 644         ce = __mb_cache_entry_find(l, index_hash_p, bdev, key);
 645         __mb_cache_entry_release_unlock(prev);
 646         return ce;
 647 }
 648
 649 #endif  /* !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0) */
 650
 651 static int __init init_mbcache(void)
 652 {
 653         register_shrinker(&mb_cache_shrinker);
 654         return 0;
 655 }
 656
 657 static void __exit exit_mbcache(void)
 658 {
 659         unregister_shrinker(&mb_cache_shrinker);
 660 }
 661
 662 module_init(init_mbcache)
 663 module_exit(exit_mbcache)
 664