Initial import

1 files changed, 858 insertions, 0 deletions

diff --git a/fs/mbcache.c b/fs/mbcache.c
new file mode 100644
index 000000000..187477ded
--- /dev/null
+++ b/fs/mbcache.c
@@ -0,0 +1,858 @@
+/*
+ * linux/fs/mbcache.c
+ * (C) 2001-2002 Andreas Gruenbacher, <a.gruenbacher@computer.org>
+ */
+
+/*
+ * Filesystem Meta Information Block Cache (mbcache)
+ *
+ * The mbcache caches blocks of block devices that need to be located
+ * by their device/block number, as well as by other criteria (such
+ * as the block's contents).
+ *
+ * There can only be one cache entry in a cache per device and block number.
+ * Additional indexes need not be unique in this sense. The number of
+ * additional indexes (=other criteria) can be hardwired at compile time
+ * or specified at cache create time.
+ *
+ * Each cache entry is of fixed size. An entry may be `valid' or `invalid'
+ * in the cache. A valid entry is in the main hash tables of the cache,
+ * and may also be in the lru list. An invalid entry is not in any hashes
+ * or lists.
+ *
+ * A valid cache entry is only in the lru list if no handles refer to it.
+ * Invalid cache entries will be freed when the last handle to the cache
+ * entry is released. Entries that cannot be freed immediately are put
+ * back on the lru list.
+ */
+
+/*
+ * Lock descriptions and usage:
+ *
+ * Each hash chain of both the block and index hash tables now contains
+ * a built-in lock used to serialize accesses to the hash chain.
+ *
+ * Accesses to global data structures mb_cache_list and mb_cache_lru_list
+ * are serialized via the global spinlock mb_cache_spinlock.
+ *
+ * Each mb_cache_entry contains a spinlock, e_entry_lock, to serialize
+ * accesses to its local data, such as e_used and e_queued.
+ *
+ * Lock ordering:
+ *
+ * Each block hash chain's lock has the highest lock order, followed by an
+ * index hash chain's lock, mb_cache_bg_lock (used to implement mb_cache_entry's
+ * lock), and mb_cach_spinlock, with the lowest order.  While holding
+ * either a block or index hash chain lock, a thread can acquire an
+ * mc_cache_bg_lock, which in turn can also acquire mb_cache_spinlock.
+ *
+ * Synchronization:
+ *
+ * Since both mb_cache_entry_get and mb_cache_entry_find scan the block and
+ * index hash chian, it needs to lock the corresponding hash chain.  For each
+ * mb_cache_entry within the chain, it needs to lock the mb_cache_entry to
+ * prevent either any simultaneous release or free on the entry and also
+ * to serialize accesses to either the e_used or e_queued member of the entry.
+ *
+ * To avoid having a dangling reference to an already freed
+ * mb_cache_entry, an mb_cache_entry is only freed when it is not on a
+ * block hash chain and also no longer being referenced, both e_used,
+ * and e_queued are 0's.  When an mb_cache_entry is explicitly freed it is
+ * first removed from a block hash chain.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+#include <linux/hash.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/list_bl.h>
+#include <linux/mbcache.h>
+#include <linux/init.h>
+#include <linux/blockgroup_lock.h>
+#include <linux/log2.h>
+
+#ifdef MB_CACHE_DEBUG
+# define mb_debug(f...) do { \
+		printk(KERN_DEBUG f); \
+		printk("\n"); \
+	} while (0)
+#define mb_assert(c) do { if (!(c)) \
+		printk(KERN_ERR "assertion " #c " failed\n"); \
+	} while(0)
+#else
+# define mb_debug(f...) do { } while(0)
+# define mb_assert(c) do { } while(0)
+#endif
+#define mb_error(f...) do { \
+		printk(KERN_ERR f); \
+		printk("\n"); \
+	} while(0)
+
+#define MB_CACHE_WRITER ((unsigned short)~0U >> 1)
+
+#define MB_CACHE_ENTRY_LOCK_BITS	ilog2(NR_BG_LOCKS)
+#define	MB_CACHE_ENTRY_LOCK_INDEX(ce)			\
+	(hash_long((unsigned long)ce, MB_CACHE_ENTRY_LOCK_BITS))
+
+static DECLARE_WAIT_QUEUE_HEAD(mb_cache_queue);
+static struct blockgroup_lock *mb_cache_bg_lock;
+static struct kmem_cache *mb_cache_kmem_cache;
+
+MODULE_AUTHOR("Andreas Gruenbacher <a.gruenbacher@computer.org>");
+MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
+MODULE_LICENSE("GPL");
+
+EXPORT_SYMBOL(mb_cache_create);
+EXPORT_SYMBOL(mb_cache_shrink);
+EXPORT_SYMBOL(mb_cache_destroy);
+EXPORT_SYMBOL(mb_cache_entry_alloc);
+EXPORT_SYMBOL(mb_cache_entry_insert);
+EXPORT_SYMBOL(mb_cache_entry_release);
+EXPORT_SYMBOL(mb_cache_entry_free);
+EXPORT_SYMBOL(mb_cache_entry_get);
+#if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0)
+EXPORT_SYMBOL(mb_cache_entry_find_first);
+EXPORT_SYMBOL(mb_cache_entry_find_next);
+#endif
+
+/*
+ * Global data: list of all mbcache's, lru list, and a spinlock for
+ * accessing cache data structures on SMP machines. The lru list is
+ * global across all mbcaches.
+ */
+
+static LIST_HEAD(mb_cache_list);
+static LIST_HEAD(mb_cache_lru_list);
+static DEFINE_SPINLOCK(mb_cache_spinlock);
+
+static inline void
+__spin_lock_mb_cache_entry(struct mb_cache_entry *ce)
+{
+	spin_lock(bgl_lock_ptr(mb_cache_bg_lock,
+		MB_CACHE_ENTRY_LOCK_INDEX(ce)));
+}
+
+static inline void
+__spin_unlock_mb_cache_entry(struct mb_cache_entry *ce)
+{
+	spin_unlock(bgl_lock_ptr(mb_cache_bg_lock,
+		MB_CACHE_ENTRY_LOCK_INDEX(ce)));
+}
+
+static inline int
+__mb_cache_entry_is_block_hashed(struct mb_cache_entry *ce)
+{
+	return !hlist_bl_unhashed(&ce->e_block_list);
+}
+
+
+static inline void
+__mb_cache_entry_unhash_block(struct mb_cache_entry *ce)
+{
+	if (__mb_cache_entry_is_block_hashed(ce))
+		hlist_bl_del_init(&ce->e_block_list);
+}
+
+static inline int
+__mb_cache_entry_is_index_hashed(struct mb_cache_entry *ce)
+{
+	return !hlist_bl_unhashed(&ce->e_index.o_list);
+}
+
+static inline void
+__mb_cache_entry_unhash_index(struct mb_cache_entry *ce)
+{
+	if (__mb_cache_entry_is_index_hashed(ce))
+		hlist_bl_del_init(&ce->e_index.o_list);
+}
+
+/*
+ * __mb_cache_entry_unhash_unlock()
+ *
+ * This function is called to unhash both the block and index hash
+ * chain.
+ * It assumes both the block and index hash chain is locked upon entry.
+ * It also unlock both hash chains both exit
+ */
+static inline void
+__mb_cache_entry_unhash_unlock(struct mb_cache_entry *ce)
+{
+	__mb_cache_entry_unhash_index(ce);
+	hlist_bl_unlock(ce->e_index_hash_p);
+	__mb_cache_entry_unhash_block(ce);
+	hlist_bl_unlock(ce->e_block_hash_p);
+}
+
+static void
+__mb_cache_entry_forget(struct mb_cache_entry *ce, gfp_t gfp_mask)
+{
+	struct mb_cache *cache = ce->e_cache;
+
+	mb_assert(!(ce->e_used || ce->e_queued || atomic_read(&ce->e_refcnt)));
+	kmem_cache_free(cache->c_entry_cache, ce);
+	atomic_dec(&cache->c_entry_count);
+}
+
+static void
+__mb_cache_entry_release(struct mb_cache_entry *ce)
+{
+	/* First lock the entry to serialize access to its local data. */
+	__spin_lock_mb_cache_entry(ce);
+	/* Wake up all processes queuing for this cache entry. */
+	if (ce->e_queued)
+		wake_up_all(&mb_cache_queue);
+	if (ce->e_used >= MB_CACHE_WRITER)
+		ce->e_used -= MB_CACHE_WRITER;
+	/*
+	 * Make sure that all cache entries on lru_list have
+	 * both e_used and e_qued of 0s.
+	 */
+	ce->e_used--;
+	if (!(ce->e_used || ce->e_queued || atomic_read(&ce->e_refcnt))) {
+		if (!__mb_cache_entry_is_block_hashed(ce)) {
+			__spin_unlock_mb_cache_entry(ce);
+			goto forget;
+		}
+		/*
+		 * Need access to lru list, first drop entry lock,
+		 * then reacquire the lock in the proper order.
+		 */
+		spin_lock(&mb_cache_spinlock);
+		if (list_empty(&ce->e_lru_list))
+			list_add_tail(&ce->e_lru_list, &mb_cache_lru_list);
+		spin_unlock(&mb_cache_spinlock);
+	}
+	__spin_unlock_mb_cache_entry(ce);
+	return;
+forget:
+	mb_assert(list_empty(&ce->e_lru_list));
+	__mb_cache_entry_forget(ce, GFP_KERNEL);
+}
+
+/*
+ * mb_cache_shrink_scan()  memory pressure callback
+ *
+ * This function is called by the kernel memory management when memory
+ * gets low.
+ *
+ * @shrink: (ignored)
+ * @sc: shrink_control passed from reclaim
+ *
+ * Returns the number of objects freed.
+ */
+static unsigned long
+mb_cache_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
+{
+	LIST_HEAD(free_list);
+	struct mb_cache_entry *entry, *tmp;
+	int nr_to_scan = sc->nr_to_scan;
+	gfp_t gfp_mask = sc->gfp_mask;
+	unsigned long freed = 0;
+
+	mb_debug("trying to free %d entries", nr_to_scan);
+	spin_lock(&mb_cache_spinlock);
+	while ((nr_to_scan-- > 0) && !list_empty(&mb_cache_lru_list)) {
+		struct mb_cache_entry *ce =
+			list_entry(mb_cache_lru_list.next,
+				struct mb_cache_entry, e_lru_list);
+		list_del_init(&ce->e_lru_list);
+		if (ce->e_used || ce->e_queued || atomic_read(&ce->e_refcnt))
+			continue;
+		spin_unlock(&mb_cache_spinlock);
+		/* Prevent any find or get operation on the entry */
+		hlist_bl_lock(ce->e_block_hash_p);
+		hlist_bl_lock(ce->e_index_hash_p);
+		/* Ignore if it is touched by a find/get */
+		if (ce->e_used || ce->e_queued || atomic_read(&ce->e_refcnt) ||
+			!list_empty(&ce->e_lru_list)) {
+			hlist_bl_unlock(ce->e_index_hash_p);
+			hlist_bl_unlock(ce->e_block_hash_p);
+			spin_lock(&mb_cache_spinlock);
+			continue;
+		}
+		__mb_cache_entry_unhash_unlock(ce);
+		list_add_tail(&ce->e_lru_list, &free_list);
+		spin_lock(&mb_cache_spinlock);
+	}
+	spin_unlock(&mb_cache_spinlock);
+
+	list_for_each_entry_safe(entry, tmp, &free_list, e_lru_list) {
+		__mb_cache_entry_forget(entry, gfp_mask);
+		freed++;
+	}
+	return freed;
+}
+
+static unsigned long
+mb_cache_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
+{
+	struct mb_cache *cache;
+	unsigned long count = 0;
+
+	spin_lock(&mb_cache_spinlock);
+	list_for_each_entry(cache, &mb_cache_list, c_cache_list) {
+		mb_debug("cache %s (%d)", cache->c_name,
+			  atomic_read(&cache->c_entry_count));
+		count += atomic_read(&cache->c_entry_count);
+	}
+	spin_unlock(&mb_cache_spinlock);
+
+	return vfs_pressure_ratio(count);
+}
+
+static struct shrinker mb_cache_shrinker = {
+	.count_objects = mb_cache_shrink_count,
+	.scan_objects = mb_cache_shrink_scan,
+	.seeks = DEFAULT_SEEKS,
+};
+
+/*
+ * mb_cache_create()  create a new cache
+ *
+ * All entries in one cache are equal size. Cache entries may be from
+ * multiple devices. If this is the first mbcache created, registers
+ * the cache with kernel memory management. Returns NULL if no more
+ * memory was available.
+ *
+ * @name: name of the cache (informal)
+ * @bucket_bits: log2(number of hash buckets)
+ */
+struct mb_cache *
+mb_cache_create(const char *name, int bucket_bits)
+{
+	int n, bucket_count = 1 << bucket_bits;
+	struct mb_cache *cache = NULL;
+
+	if (!mb_cache_bg_lock) {
+		mb_cache_bg_lock = kmalloc(sizeof(struct blockgroup_lock),
+			GFP_KERNEL);
+		if (!mb_cache_bg_lock)
+			return NULL;
+		bgl_lock_init(mb_cache_bg_lock);
+	}
+
+	cache = kmalloc(sizeof(struct mb_cache), GFP_KERNEL);
+	if (!cache)
+		return NULL;
+	cache->c_name = name;
+	atomic_set(&cache->c_entry_count, 0);
+	cache->c_bucket_bits = bucket_bits;
+	cache->c_block_hash = kmalloc(bucket_count *
+		sizeof(struct hlist_bl_head), GFP_KERNEL);
+	if (!cache->c_block_hash)
+		goto fail;
+	for (n=0; n<bucket_count; n++)
+		INIT_HLIST_BL_HEAD(&cache->c_block_hash[n]);
+	cache->c_index_hash = kmalloc(bucket_count *
+		sizeof(struct hlist_bl_head), GFP_KERNEL);
+	if (!cache->c_index_hash)
+		goto fail;
+	for (n=0; n<bucket_count; n++)
+		INIT_HLIST_BL_HEAD(&cache->c_index_hash[n]);
+	if (!mb_cache_kmem_cache) {
+		mb_cache_kmem_cache = kmem_cache_create(name,
+			sizeof(struct mb_cache_entry), 0,
+			SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
+		if (!mb_cache_kmem_cache)
+			goto fail2;
+	}
+	cache->c_entry_cache = mb_cache_kmem_cache;
+
+	/*
+	 * Set an upper limit on the number of cache entries so that the hash
+	 * chains won't grow too long.
+	 */
+	cache->c_max_entries = bucket_count << 4;
+
+	spin_lock(&mb_cache_spinlock);
+	list_add(&cache->c_cache_list, &mb_cache_list);
+	spin_unlock(&mb_cache_spinlock);
+	return cache;
+
+fail2:
+	kfree(cache->c_index_hash);
+
+fail:
+	kfree(cache->c_block_hash);
+	kfree(cache);
+	return NULL;
+}
+
+
+/*
+ * mb_cache_shrink()
+ *
+ * Removes all cache entries of a device from the cache. All cache entries
+ * currently in use cannot be freed, and thus remain in the cache. All others
+ * are freed.
+ *
+ * @bdev: which device's cache entries to shrink
+ */
+void
+mb_cache_shrink(struct block_device *bdev)
+{
+	LIST_HEAD(free_list);
+	struct list_head *l;
+	struct mb_cache_entry *ce, *tmp;
+
+	l = &mb_cache_lru_list;
+	spin_lock(&mb_cache_spinlock);
+	while (!list_is_last(l, &mb_cache_lru_list)) {
+		l = l->next;
+		ce = list_entry(l, struct mb_cache_entry, e_lru_list);
+		if (ce->e_bdev == bdev) {
+			list_del_init(&ce->e_lru_list);
+			if (ce->e_used || ce->e_queued ||
+				atomic_read(&ce->e_refcnt))
+				continue;
+			spin_unlock(&mb_cache_spinlock);
+			/*
+			 * Prevent any find or get operation on the entry.
+			 */
+			hlist_bl_lock(ce->e_block_hash_p);
+			hlist_bl_lock(ce->e_index_hash_p);
+			/* Ignore if it is touched by a find/get */
+			if (ce->e_used || ce->e_queued ||
+				atomic_read(&ce->e_refcnt) ||
+				!list_empty(&ce->e_lru_list)) {
+				hlist_bl_unlock(ce->e_index_hash_p);
+				hlist_bl_unlock(ce->e_block_hash_p);
+				l = &mb_cache_lru_list;
+				spin_lock(&mb_cache_spinlock);
+				continue;
+			}
+			__mb_cache_entry_unhash_unlock(ce);
+			mb_assert(!(ce->e_used || ce->e_queued ||
+				atomic_read(&ce->e_refcnt)));
+			list_add_tail(&ce->e_lru_list, &free_list);
+			l = &mb_cache_lru_list;
+			spin_lock(&mb_cache_spinlock);
+		}
+	}
+	spin_unlock(&mb_cache_spinlock);
+
+	list_for_each_entry_safe(ce, tmp, &free_list, e_lru_list) {
+		__mb_cache_entry_forget(ce, GFP_KERNEL);
+	}
+}
+
+
+/*
+ * mb_cache_destroy()
+ *
+ * Shrinks the cache to its minimum possible size (hopefully 0 entries),
+ * and then destroys it. If this was the last mbcache, un-registers the
+ * mbcache from kernel memory management.
+ */
+void
+mb_cache_destroy(struct mb_cache *cache)
+{
+	LIST_HEAD(free_list);
+	struct mb_cache_entry *ce, *tmp;
+
+	spin_lock(&mb_cache_spinlock);
+	list_for_each_entry_safe(ce, tmp, &mb_cache_lru_list, e_lru_list) {
+		if (ce->e_cache == cache)
+			list_move_tail(&ce->e_lru_list, &free_list);
+	}
+	list_del(&cache->c_cache_list);
+	spin_unlock(&mb_cache_spinlock);
+
+	list_for_each_entry_safe(ce, tmp, &free_list, e_lru_list) {
+		list_del_init(&ce->e_lru_list);
+		/*
+		 * Prevent any find or get operation on the entry.
+		 */
+		hlist_bl_lock(ce->e_block_hash_p);
+		hlist_bl_lock(ce->e_index_hash_p);
+		mb_assert(!(ce->e_used || ce->e_queued ||
+			atomic_read(&ce->e_refcnt)));
+		__mb_cache_entry_unhash_unlock(ce);
+		__mb_cache_entry_forget(ce, GFP_KERNEL);
+	}
+
+	if (atomic_read(&cache->c_entry_count) > 0) {
+		mb_error("cache %s: %d orphaned entries",
+			  cache->c_name,
+			  atomic_read(&cache->c_entry_count));
+	}
+
+	if (list_empty(&mb_cache_list)) {
+		kmem_cache_destroy(mb_cache_kmem_cache);
+		mb_cache_kmem_cache = NULL;
+	}
+	kfree(cache->c_index_hash);
+	kfree(cache->c_block_hash);
+	kfree(cache);
+}
+
+/*
+ * mb_cache_entry_alloc()
+ *
+ * Allocates a new cache entry. The new entry will not be valid initially,
+ * and thus cannot be looked up yet. It should be filled with data, and
+ * then inserted into the cache using mb_cache_entry_insert(). Returns NULL
+ * if no more memory was available.
+ */
+struct mb_cache_entry *
+mb_cache_entry_alloc(struct mb_cache *cache, gfp_t gfp_flags)
+{
+	struct mb_cache_entry *ce;
+
+	if (atomic_read(&cache->c_entry_count) >= cache->c_max_entries) {
+		struct list_head *l;
+
+		l = &mb_cache_lru_list;
+		spin_lock(&mb_cache_spinlock);
+		while (!list_is_last(l, &mb_cache_lru_list)) {
+			l = l->next;
+			ce = list_entry(l, struct mb_cache_entry, e_lru_list);
+			if (ce->e_cache == cache) {
+				list_del_init(&ce->e_lru_list);
+				if (ce->e_used || ce->e_queued ||
+					atomic_read(&ce->e_refcnt))
+					continue;
+				spin_unlock(&mb_cache_spinlock);
+				/*
+				 * Prevent any find or get operation on the
+				 * entry.
+				 */
+				hlist_bl_lock(ce->e_block_hash_p);
+				hlist_bl_lock(ce->e_index_hash_p);
+				/* Ignore if it is touched by a find/get */
+				if (ce->e_used || ce->e_queued ||
+					atomic_read(&ce->e_refcnt) ||
+					!list_empty(&ce->e_lru_list)) {
+					hlist_bl_unlock(ce->e_index_hash_p);
+					hlist_bl_unlock(ce->e_block_hash_p);
+					l = &mb_cache_lru_list;
+					spin_lock(&mb_cache_spinlock);
+					continue;
+				}
+				mb_assert(list_empty(&ce->e_lru_list));
+				mb_assert(!(ce->e_used || ce->e_queued ||
+					atomic_read(&ce->e_refcnt)));
+				__mb_cache_entry_unhash_unlock(ce);
+				goto found;
+			}
+		}
+		spin_unlock(&mb_cache_spinlock);
+	}
+
+	ce = kmem_cache_alloc(cache->c_entry_cache, gfp_flags);
+	if (!ce)
+		return NULL;
+	atomic_inc(&cache->c_entry_count);
+	INIT_LIST_HEAD(&ce->e_lru_list);
+	INIT_HLIST_BL_NODE(&ce->e_block_list);
+	INIT_HLIST_BL_NODE(&ce->e_index.o_list);
+	ce->e_cache = cache;
+	ce->e_queued = 0;
+	atomic_set(&ce->e_refcnt, 0);
+found:
+	ce->e_block_hash_p = &cache->c_block_hash[0];
+	ce->e_index_hash_p = &cache->c_index_hash[0];
+	ce->e_used = 1 + MB_CACHE_WRITER;
+	return ce;
+}
+
+
+/*
+ * mb_cache_entry_insert()
+ *
+ * Inserts an entry that was allocated using mb_cache_entry_alloc() into
+ * the cache. After this, the cache entry can be looked up, but is not yet
+ * in the lru list as the caller still holds a handle to it. Returns 0 on
+ * success, or -EBUSY if a cache entry for that device + inode exists
+ * already (this may happen after a failed lookup, but when another process
+ * has inserted the same cache entry in the meantime).
+ *
+ * @bdev: device the cache entry belongs to
+ * @block: block number
+ * @key: lookup key
+ */
+int
+mb_cache_entry_insert(struct mb_cache_entry *ce, struct block_device *bdev,
+		      sector_t block, unsigned int key)
+{
+	struct mb_cache *cache = ce->e_cache;
+	unsigned int bucket;
+	struct hlist_bl_node *l;
+	struct hlist_bl_head *block_hash_p;
+	struct hlist_bl_head *index_hash_p;
+	struct mb_cache_entry *lce;
+
+	mb_assert(ce);
+	bucket = hash_long((unsigned long)bdev + (block & 0xffffffff), 
+			   cache->c_bucket_bits);
+	block_hash_p = &cache->c_block_hash[bucket];
+	hlist_bl_lock(block_hash_p);
+	hlist_bl_for_each_entry(lce, l, block_hash_p, e_block_list) {
+		if (lce->e_bdev == bdev && lce->e_block == block) {
+			hlist_bl_unlock(block_hash_p);
+			return -EBUSY;
+		}
+	}
+	mb_assert(!__mb_cache_entry_is_block_hashed(ce));
+	__mb_cache_entry_unhash_block(ce);
+	__mb_cache_entry_unhash_index(ce);
+	ce->e_bdev = bdev;
+	ce->e_block = block;
+	ce->e_block_hash_p = block_hash_p;
+	ce->e_index.o_key = key;
+	hlist_bl_add_head(&ce->e_block_list, block_hash_p);
+	hlist_bl_unlock(block_hash_p);
+	bucket = hash_long(key, cache->c_bucket_bits);
+	index_hash_p = &cache->c_index_hash[bucket];
+	hlist_bl_lock(index_hash_p);
+	ce->e_index_hash_p = index_hash_p;
+	hlist_bl_add_head(&ce->e_index.o_list, index_hash_p);
+	hlist_bl_unlock(index_hash_p);
+	return 0;
+}
+
+
+/*
+ * mb_cache_entry_release()
+ *
+ * Release a handle to a cache entry. When the last handle to a cache entry
+ * is released it is either freed (if it is invalid) or otherwise inserted
+ * in to the lru list.
+ */
+void
+mb_cache_entry_release(struct mb_cache_entry *ce)
+{
+	__mb_cache_entry_release(ce);
+}
+
+
+/*
+ * mb_cache_entry_free()
+ *
+ */
+void
+mb_cache_entry_free(struct mb_cache_entry *ce)
+{
+	mb_assert(ce);
+	mb_assert(list_empty(&ce->e_lru_list));
+	hlist_bl_lock(ce->e_index_hash_p);
+	__mb_cache_entry_unhash_index(ce);
+	hlist_bl_unlock(ce->e_index_hash_p);
+	hlist_bl_lock(ce->e_block_hash_p);
+	__mb_cache_entry_unhash_block(ce);
+	hlist_bl_unlock(ce->e_block_hash_p);
+	__mb_cache_entry_release(ce);
+}
+
+
+/*
+ * mb_cache_entry_get()
+ *
+ * Get a cache entry  by device / block number. (There can only be one entry
+ * in the cache per device and block.) Returns NULL if no such cache entry
+ * exists. The returned cache entry is locked for exclusive access ("single
+ * writer").
+ */
+struct mb_cache_entry *
+mb_cache_entry_get(struct mb_cache *cache, struct block_device *bdev,
+		   sector_t block)
+{
+	unsigned int bucket;
+	struct hlist_bl_node *l;
+	struct mb_cache_entry *ce;
+	struct hlist_bl_head *block_hash_p;
+
+	bucket = hash_long((unsigned long)bdev + (block & 0xffffffff),
+			   cache->c_bucket_bits);
+	block_hash_p = &cache->c_block_hash[bucket];
+	/* First serialize access to the block corresponding hash chain. */
+	hlist_bl_lock(block_hash_p);
+	hlist_bl_for_each_entry(ce, l, block_hash_p, e_block_list) {
+		mb_assert(ce->e_block_hash_p == block_hash_p);
+		if (ce->e_bdev == bdev && ce->e_block == block) {
+			/*
+			 * Prevent a free from removing the entry.
+			 */
+			atomic_inc(&ce->e_refcnt);
+			hlist_bl_unlock(block_hash_p);
+			__spin_lock_mb_cache_entry(ce);
+			atomic_dec(&ce->e_refcnt);
+			if (ce->e_used > 0) {
+				DEFINE_WAIT(wait);
+				while (ce->e_used > 0) {
+					ce->e_queued++;
+					prepare_to_wait(&mb_cache_queue, &wait,
+							TASK_UNINTERRUPTIBLE);
+					__spin_unlock_mb_cache_entry(ce);
+					schedule();
+					__spin_lock_mb_cache_entry(ce);
+					ce->e_queued--;
+				}
+				finish_wait(&mb_cache_queue, &wait);
+			}
+			ce->e_used += 1 + MB_CACHE_WRITER;
+			__spin_unlock_mb_cache_entry(ce);
+
+			if (!list_empty(&ce->e_lru_list)) {
+				spin_lock(&mb_cache_spinlock);
+				list_del_init(&ce->e_lru_list);
+				spin_unlock(&mb_cache_spinlock);
+			}
+			if (!__mb_cache_entry_is_block_hashed(ce)) {
+				__mb_cache_entry_release(ce);
+				return NULL;
+			}
+			return ce;
+		}
+	}
+	hlist_bl_unlock(block_hash_p);
+	return NULL;
+}
+
+#if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0)
+
+static struct mb_cache_entry *
+__mb_cache_entry_find(struct hlist_bl_node *l, struct hlist_bl_head *head,
+		      struct block_device *bdev, unsigned int key)
+{
+
+	/* The index hash chain is alredy acquire by caller. */
+	while (l != NULL) {
+		struct mb_cache_entry *ce =
+			hlist_bl_entry(l, struct mb_cache_entry,
+				e_index.o_list);
+		mb_assert(ce->e_index_hash_p == head);
+		if (ce->e_bdev == bdev && ce->e_index.o_key == key) {
+			/*
+			 * Prevent a free from removing the entry.
+			 */
+			atomic_inc(&ce->e_refcnt);
+			hlist_bl_unlock(head);
+			__spin_lock_mb_cache_entry(ce);
+			atomic_dec(&ce->e_refcnt);
+			ce->e_used++;
+			/* Incrementing before holding the lock gives readers
+			   priority over writers. */
+			if (ce->e_used >= MB_CACHE_WRITER) {
+				DEFINE_WAIT(wait);
+
+				while (ce->e_used >= MB_CACHE_WRITER) {
+					ce->e_queued++;
+					prepare_to_wait(&mb_cache_queue, &wait,
+							TASK_UNINTERRUPTIBLE);
+					__spin_unlock_mb_cache_entry(ce);
+					schedule();
+					__spin_lock_mb_cache_entry(ce);
+					ce->e_queued--;
+				}
+				finish_wait(&mb_cache_queue, &wait);
+			}
+			__spin_unlock_mb_cache_entry(ce);
+			if (!list_empty(&ce->e_lru_list)) {
+				spin_lock(&mb_cache_spinlock);
+				list_del_init(&ce->e_lru_list);
+				spin_unlock(&mb_cache_spinlock);
+			}
+			if (!__mb_cache_entry_is_block_hashed(ce)) {
+				__mb_cache_entry_release(ce);
+				return ERR_PTR(-EAGAIN);
+			}
+			return ce;
+		}
+		l = l->next;
+	}
+	hlist_bl_unlock(head);
+	return NULL;
+}
+
+
+/*
+ * mb_cache_entry_find_first()
+ *
+ * Find the first cache entry on a given device with a certain key in
+ * an additional index. Additional matches can be found with
+ * mb_cache_entry_find_next(). Returns NULL if no match was found. The
+ * returned cache entry is locked for shared access ("multiple readers").
+ *
+ * @cache: the cache to search
+ * @bdev: the device the cache entry should belong to
+ * @key: the key in the index
+ */
+struct mb_cache_entry *
+mb_cache_entry_find_first(struct mb_cache *cache, struct block_device *bdev,
+			  unsigned int key)
+{
+	unsigned int bucket = hash_long(key, cache->c_bucket_bits);
+	struct hlist_bl_node *l;
+	struct mb_cache_entry *ce = NULL;
+	struct hlist_bl_head *index_hash_p;
+
+	index_hash_p = &cache->c_index_hash[bucket];
+	hlist_bl_lock(index_hash_p);
+	if (!hlist_bl_empty(index_hash_p)) {
+		l = hlist_bl_first(index_hash_p);
+		ce = __mb_cache_entry_find(l, index_hash_p, bdev, key);
+	} else
+		hlist_bl_unlock(index_hash_p);
+	return ce;
+}
+
+
+/*
+ * mb_cache_entry_find_next()
+ *
+ * Find the next cache entry on a given device with a certain key in an
+ * additional index. Returns NULL if no match could be found. The previous
+ * entry is atomatically released, so that mb_cache_entry_find_next() can
+ * be called like this:
+ *
+ * entry = mb_cache_entry_find_first();
+ * while (entry) {
+ * 	...
+ *	entry = mb_cache_entry_find_next(entry, ...);
+ * }
+ *
+ * @prev: The previous match
+ * @bdev: the device the cache entry should belong to
+ * @key: the key in the index
+ */
+struct mb_cache_entry *
+mb_cache_entry_find_next(struct mb_cache_entry *prev,
+			 struct block_device *bdev, unsigned int key)
+{
+	struct mb_cache *cache = prev->e_cache;
+	unsigned int bucket = hash_long(key, cache->c_bucket_bits);
+	struct hlist_bl_node *l;
+	struct mb_cache_entry *ce;
+	struct hlist_bl_head *index_hash_p;
+
+	index_hash_p = &cache->c_index_hash[bucket];
+	mb_assert(prev->e_index_hash_p == index_hash_p);
+	hlist_bl_lock(index_hash_p);
+	mb_assert(!hlist_bl_empty(index_hash_p));
+	l = prev->e_index.o_list.next;
+	ce = __mb_cache_entry_find(l, index_hash_p, bdev, key);
+	__mb_cache_entry_release(prev);
+	return ce;
+}
+
+#endif  /* !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0) */
+
+static int __init init_mbcache(void)
+{
+	register_shrinker(&mb_cache_shrinker);
+	return 0;
+}
+
+static void __exit exit_mbcache(void)
+{
+	unregister_shrinker(&mb_cache_shrinker);
+}
+
+module_init(init_mbcache)
+module_exit(exit_mbcache)
+