/*
   * 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.
   */
  
  #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/init.h>
  #include <linux/mbcache.h>
  
  
  #ifdef MB_CACHE_DEBUG
  # define mb_debug(f...) do { \
  		printk(KERN_DEBUG f); \
  		printk("
  "); \
  	} while (0)
  #define mb_assert(c) do { if (!(c)) \
  		printk(KERN_ERR "assertion " #c " failed
  "); \
  	} 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("
  "); \
  	} while(0)
  
  #define MB_CACHE_WRITER ((unsigned short)~0U >> 1)

  static DECLARE_WAIT_QUEUE_HEAD(mb_cache_queue);

  		
  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);

  /*
   * What the mbcache registers as to get shrunk dynamically.
   */

  static int mb_cache_shrink_fn(struct shrinker *shrink,
  			      struct shrink_control *sc);

  static struct shrinker mb_cache_shrinker = {
  	.shrink = mb_cache_shrink_fn,
  	.seeks = DEFAULT_SEEKS,
  };

  
  static inline int
  __mb_cache_entry_is_hashed(struct mb_cache_entry *ce)
  {
  	return !list_empty(&ce->e_block_list);
  }

  static void

  __mb_cache_entry_unhash(struct mb_cache_entry *ce)
  {

  	if (__mb_cache_entry_is_hashed(ce)) {
  		list_del_init(&ce->e_block_list);

  		list_del(&ce->e_index.o_list);

  	}
  }

  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));

  	kmem_cache_free(cache->c_entry_cache, ce);
  	atomic_dec(&cache->c_entry_count);

  }

  static void

  __mb_cache_entry_release_unlock(struct mb_cache_entry *ce)

  	__releases(mb_cache_spinlock)

  {
  	/* 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;
  	ce->e_used--;
  	if (!(ce->e_used || ce->e_queued)) {
  		if (!__mb_cache_entry_is_hashed(ce))
  			goto forget;
  		mb_assert(list_empty(&ce->e_lru_list));
  		list_add_tail(&ce->e_lru_list, &mb_cache_lru_list);
  	}
  	spin_unlock(&mb_cache_spinlock);
  	return;
  forget:
  	spin_unlock(&mb_cache_spinlock);
  	__mb_cache_entry_forget(ce, GFP_KERNEL);
  }
  
  
  /*
   * mb_cache_shrink_fn()  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 which are present in the cache.
   */
  static int

  mb_cache_shrink_fn(struct shrinker *shrink, struct shrink_control *sc)

  {
  	LIST_HEAD(free_list);

  	struct mb_cache *cache;
  	struct mb_cache_entry *entry, *tmp;

  	int count = 0;

  	int nr_to_scan = sc->nr_to_scan;
  	gfp_t gfp_mask = sc->gfp_mask;

  	mb_debug("trying to free %d entries", nr_to_scan);

  	spin_lock(&mb_cache_spinlock);

  	while (nr_to_scan-- && !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_move_tail(&ce->e_lru_list, &free_list);
  		__mb_cache_entry_unhash(ce);
  	}

  	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);

  	list_for_each_entry_safe(entry, tmp, &free_list, e_lru_list) {
  		__mb_cache_entry_forget(entry, gfp_mask);

  	}

  	return (count / 100) * sysctl_vfs_cache_pressure;
  }
  
  
  /*
   * 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;

  	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 list_head),
  	                              GFP_KERNEL);
  	if (!cache->c_block_hash)
  		goto fail;
  	for (n=0; n<bucket_count; n++)
  		INIT_LIST_HEAD(&cache->c_block_hash[n]);

  	cache->c_index_hash = kmalloc(bucket_count * sizeof(struct list_head),
  				      GFP_KERNEL);
  	if (!cache->c_index_hash)
  		goto fail;
  	for (n=0; n<bucket_count; n++)
  		INIT_LIST_HEAD(&cache->c_index_hash[n]);
  	cache->c_entry_cache = kmem_cache_create(name,
  		sizeof(struct mb_cache_entry), 0,

  		SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);

  	if (!cache->c_entry_cache)

  		goto fail2;

  	/*
  	 * 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, *ltmp;
  
  	spin_lock(&mb_cache_spinlock);
  	list_for_each_safe(l, ltmp, &mb_cache_lru_list) {
  		struct mb_cache_entry *ce =
  			list_entry(l, struct mb_cache_entry, e_lru_list);
  		if (ce->e_bdev == bdev) {
  			list_move_tail(&ce->e_lru_list, &free_list);
  			__mb_cache_entry_unhash(ce);
  		}
  	}
  	spin_unlock(&mb_cache_spinlock);
  	list_for_each_safe(l, ltmp, &free_list) {
  		__mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
  						   e_lru_list), 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 list_head *l, *ltmp;

  
  	spin_lock(&mb_cache_spinlock);
  	list_for_each_safe(l, ltmp, &mb_cache_lru_list) {
  		struct mb_cache_entry *ce =
  			list_entry(l, struct mb_cache_entry, e_lru_list);
  		if (ce->e_cache == cache) {
  			list_move_tail(&ce->e_lru_list, &free_list);
  			__mb_cache_entry_unhash(ce);
  		}
  	}
  	list_del(&cache->c_cache_list);
  	spin_unlock(&mb_cache_spinlock);
  
  	list_for_each_safe(l, ltmp, &free_list) {
  		__mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
  						   e_lru_list), 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));
  	}
  
  	kmem_cache_destroy(cache->c_entry_cache);

  	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 = NULL;
  
  	if (atomic_read(&cache->c_entry_count) >= cache->c_max_entries) {
  		spin_lock(&mb_cache_spinlock);
  		if (!list_empty(&mb_cache_lru_list)) {
  			ce = list_entry(mb_cache_lru_list.next,
  					struct mb_cache_entry, e_lru_list);
  			list_del_init(&ce->e_lru_list);
  			__mb_cache_entry_unhash(ce);
  		}
  		spin_unlock(&mb_cache_spinlock);
  	}
  	if (!ce) {
  		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_LIST_HEAD(&ce->e_block_list);
  		ce->e_cache = cache;

  		ce->e_queued = 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 list_head *l;

  	int error = -EBUSY;

  
  	bucket = hash_long((unsigned long)bdev + (block & 0xffffffff), 
  			   cache->c_bucket_bits);
  	spin_lock(&mb_cache_spinlock);
  	list_for_each_prev(l, &cache->c_block_hash[bucket]) {
  		struct mb_cache_entry *ce =
  			list_entry(l, struct mb_cache_entry, e_block_list);
  		if (ce->e_bdev == bdev && ce->e_block == block)
  			goto out;
  	}
  	__mb_cache_entry_unhash(ce);
  	ce->e_bdev = bdev;
  	ce->e_block = block;
  	list_add(&ce->e_block_list, &cache->c_block_hash[bucket]);

  	ce->e_index.o_key = key;
  	bucket = hash_long(key, cache->c_bucket_bits);
  	list_add(&ce->e_index.o_list, &cache->c_index_hash[bucket]);

  	error = 0;
  out:
  	spin_unlock(&mb_cache_spinlock);
  	return error;
  }
  
  
  /*
   * 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)
  {
  	spin_lock(&mb_cache_spinlock);
  	__mb_cache_entry_release_unlock(ce);
  }
  
  
  /*
   * mb_cache_entry_free()
   *
   * This is equivalent to the sequence mb_cache_entry_takeout() --
   * mb_cache_entry_release().
   */
  void
  mb_cache_entry_free(struct mb_cache_entry *ce)
  {
  	spin_lock(&mb_cache_spinlock);
  	mb_assert(list_empty(&ce->e_lru_list));
  	__mb_cache_entry_unhash(ce);
  	__mb_cache_entry_release_unlock(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 list_head *l;
  	struct mb_cache_entry *ce;
  
  	bucket = hash_long((unsigned long)bdev + (block & 0xffffffff),
  			   cache->c_bucket_bits);
  	spin_lock(&mb_cache_spinlock);
  	list_for_each(l, &cache->c_block_hash[bucket]) {
  		ce = list_entry(l, struct mb_cache_entry, e_block_list);
  		if (ce->e_bdev == bdev && ce->e_block == block) {
  			DEFINE_WAIT(wait);
  
  			if (!list_empty(&ce->e_lru_list))
  				list_del_init(&ce->e_lru_list);
  
  			while (ce->e_used > 0) {
  				ce->e_queued++;
  				prepare_to_wait(&mb_cache_queue, &wait,
  						TASK_UNINTERRUPTIBLE);
  				spin_unlock(&mb_cache_spinlock);
  				schedule();
  				spin_lock(&mb_cache_spinlock);
  				ce->e_queued--;
  			}
  			finish_wait(&mb_cache_queue, &wait);
  			ce->e_used += 1 + MB_CACHE_WRITER;
  
  			if (!__mb_cache_entry_is_hashed(ce)) {
  				__mb_cache_entry_release_unlock(ce);
  				return NULL;
  			}
  			goto cleanup;
  		}
  	}
  	ce = NULL;
  
  cleanup:
  	spin_unlock(&mb_cache_spinlock);
  	return ce;
  }
  
  #if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0)
  
  static struct mb_cache_entry *
  __mb_cache_entry_find(struct list_head *l, struct list_head *head,

  		      struct block_device *bdev, unsigned int key)

  {
  	while (l != head) {
  		struct mb_cache_entry *ce =

  			list_entry(l, struct mb_cache_entry, e_index.o_list);
  		if (ce->e_bdev == bdev && ce->e_index.o_key == key) {

  			DEFINE_WAIT(wait);
  
  			if (!list_empty(&ce->e_lru_list))
  				list_del_init(&ce->e_lru_list);
  
  			/* Incrementing before holding the lock gives readers
  			   priority over writers. */
  			ce->e_used++;
  			while (ce->e_used >= MB_CACHE_WRITER) {
  				ce->e_queued++;
  				prepare_to_wait(&mb_cache_queue, &wait,
  						TASK_UNINTERRUPTIBLE);
  				spin_unlock(&mb_cache_spinlock);
  				schedule();
  				spin_lock(&mb_cache_spinlock);
  				ce->e_queued--;
  			}
  			finish_wait(&mb_cache_queue, &wait);
  
  			if (!__mb_cache_entry_is_hashed(ce)) {
  				__mb_cache_entry_release_unlock(ce);
  				spin_lock(&mb_cache_spinlock);
  				return ERR_PTR(-EAGAIN);
  			}
  			return ce;
  		}
  		l = l->next;
  	}
  	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 list_head *l;
  	struct mb_cache_entry *ce;

  	spin_lock(&mb_cache_spinlock);

  	l = cache->c_index_hash[bucket].next;
  	ce = __mb_cache_entry_find(l, &cache->c_index_hash[bucket], bdev, key);

  	spin_unlock(&mb_cache_spinlock);
  	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 list_head *l;
  	struct mb_cache_entry *ce;

  	spin_lock(&mb_cache_spinlock);

  	l = prev->e_index.o_list.next;
  	ce = __mb_cache_entry_find(l, &cache->c_index_hash[bucket], bdev, key);

  	__mb_cache_entry_release_unlock(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)