/*
   * linux/fs/inode.c
   *
   * (C) 1997 Linus Torvalds
   */

  #include <linux/fs.h>
  #include <linux/mm.h>
  #include <linux/dcache.h>
  #include <linux/init.h>
  #include <linux/quotaops.h>
  #include <linux/slab.h>
  #include <linux/writeback.h>
  #include <linux/module.h>
  #include <linux/backing-dev.h>
  #include <linux/wait.h>
  #include <linux/hash.h>
  #include <linux/swap.h>
  #include <linux/security.h>
  #include <linux/pagemap.h>
  #include <linux/cdev.h>
  #include <linux/bootmem.h>

  #include <linux/inotify.h>

  #include <linux/mount.h>

  
  /*
   * This is needed for the following functions:
   *  - inode_has_buffers
   *  - invalidate_inode_buffers

   *  - invalidate_bdev
   *
   * FIXME: remove all knowledge of the buffer layer from this file
   */
  #include <linux/buffer_head.h>
  
  /*
   * New inode.c implementation.
   *
   * This implementation has the basic premise of trying
   * to be extremely low-overhead and SMP-safe, yet be
   * simple enough to be "obviously correct".
   *
   * Famous last words.
   */
  
  /* inode dynamic allocation 1999, Andrea Arcangeli <andrea@suse.de> */
  
  /* #define INODE_PARANOIA 1 */
  /* #define INODE_DEBUG 1 */
  
  /*
   * Inode lookup is no longer as critical as it used to be:
   * most of the lookups are going to be through the dcache.
   */
  #define I_HASHBITS	i_hash_shift
  #define I_HASHMASK	i_hash_mask

  static unsigned int i_hash_mask __read_mostly;
  static unsigned int i_hash_shift __read_mostly;

  
  /*
   * Each inode can be on two separate lists. One is
   * the hash list of the inode, used for lookups. The
   * other linked list is the "type" list:
   *  "in_use" - valid inode, i_count > 0, i_nlink > 0
   *  "dirty"  - as "in_use" but also dirty
   *  "unused" - valid inode, i_count = 0
   *
   * A "dirty" list is maintained for each super block,
   * allowing for low-overhead inode sync() operations.
   */
  
  LIST_HEAD(inode_in_use);
  LIST_HEAD(inode_unused);

  static struct hlist_head *inode_hashtable __read_mostly;

  
  /*
   * A simple spinlock to protect the list manipulations.
   *
   * NOTE! You also have to own the lock if you change
   * the i_state of an inode while it is in use..
   */
  DEFINE_SPINLOCK(inode_lock);
  
  /*

   * iprune_mutex provides exclusion between the kswapd or try_to_free_pages

   * icache shrinking path, and the umount path.  Without this exclusion,
   * by the time prune_icache calls iput for the inode whose pages it has
   * been invalidating, or by the time it calls clear_inode & destroy_inode
   * from its final dispose_list, the struct super_block they refer to
   * (for inode->i_sb->s_op) may already have been freed and reused.
   */

  static DEFINE_MUTEX(iprune_mutex);

  
  /*
   * Statistics gathering..
   */
  struct inodes_stat_t inodes_stat;

  static struct kmem_cache * inode_cachep __read_mostly;

  
  static struct inode *alloc_inode(struct super_block *sb)
  {

  	static const struct address_space_operations empty_aops;

  	static struct inode_operations empty_iops;

  	static const struct file_operations empty_fops;

  	struct inode *inode;
  
  	if (sb->s_op->alloc_inode)
  		inode = sb->s_op->alloc_inode(sb);
  	else

  		inode = (struct inode *) kmem_cache_alloc(inode_cachep, GFP_KERNEL);

  
  	if (inode) {
  		struct address_space * const mapping = &inode->i_data;
  
  		inode->i_sb = sb;
  		inode->i_blkbits = sb->s_blocksize_bits;
  		inode->i_flags = 0;
  		atomic_set(&inode->i_count, 1);
  		inode->i_op = &empty_iops;
  		inode->i_fop = &empty_fops;
  		inode->i_nlink = 1;
  		atomic_set(&inode->i_writecount, 0);
  		inode->i_size = 0;
  		inode->i_blocks = 0;
  		inode->i_bytes = 0;
  		inode->i_generation = 0;
  #ifdef CONFIG_QUOTA
  		memset(&inode->i_dquot, 0, sizeof(inode->i_dquot));
  #endif
  		inode->i_pipe = NULL;
  		inode->i_bdev = NULL;
  		inode->i_cdev = NULL;
  		inode->i_rdev = 0;

  		inode->dirtied_when = 0;
  		if (security_inode_alloc(inode)) {
  			if (inode->i_sb->s_op->destroy_inode)
  				inode->i_sb->s_op->destroy_inode(inode);
  			else
  				kmem_cache_free(inode_cachep, (inode));
  			return NULL;
  		}
  
  		mapping->a_ops = &empty_aops;
   		mapping->host = inode;
  		mapping->flags = 0;
  		mapping_set_gfp_mask(mapping, GFP_HIGHUSER);
  		mapping->assoc_mapping = NULL;
  		mapping->backing_dev_info = &default_backing_dev_info;
  
  		/*
  		 * If the block_device provides a backing_dev_info for client
  		 * inodes then use that.  Otherwise the inode share the bdev's
  		 * backing_dev_info.
  		 */
  		if (sb->s_bdev) {
  			struct backing_dev_info *bdi;
  
  			bdi = sb->s_bdev->bd_inode_backing_dev_info;
  			if (!bdi)
  				bdi = sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
  			mapping->backing_dev_info = bdi;
  		}

  		inode->i_private = NULL;

  		inode->i_mapping = mapping;
  	}
  	return inode;
  }
  
  void destroy_inode(struct inode *inode) 
  {

  	BUG_ON(inode_has_buffers(inode));

  	security_inode_free(inode);
  	if (inode->i_sb->s_op->destroy_inode)
  		inode->i_sb->s_op->destroy_inode(inode);
  	else
  		kmem_cache_free(inode_cachep, (inode));
  }
  
  
  /*
   * These are initializations that only need to be done
   * once, because the fields are idempotent across use
   * of the inode, so let the slab aware of that.
   */
  void inode_init_once(struct inode *inode)
  {
  	memset(inode, 0, sizeof(*inode));
  	INIT_HLIST_NODE(&inode->i_hash);
  	INIT_LIST_HEAD(&inode->i_dentry);
  	INIT_LIST_HEAD(&inode->i_devices);

  	mutex_init(&inode->i_mutex);

  	init_rwsem(&inode->i_alloc_sem);
  	INIT_RADIX_TREE(&inode->i_data.page_tree, GFP_ATOMIC);
  	rwlock_init(&inode->i_data.tree_lock);
  	spin_lock_init(&inode->i_data.i_mmap_lock);
  	INIT_LIST_HEAD(&inode->i_data.private_list);
  	spin_lock_init(&inode->i_data.private_lock);
  	INIT_RAW_PRIO_TREE_ROOT(&inode->i_data.i_mmap);
  	INIT_LIST_HEAD(&inode->i_data.i_mmap_nonlinear);
  	spin_lock_init(&inode->i_lock);
  	i_size_ordered_init(inode);

  #ifdef CONFIG_INOTIFY
  	INIT_LIST_HEAD(&inode->inotify_watches);

  	mutex_init(&inode->inotify_mutex);

  #endif

  }
  
  EXPORT_SYMBOL(inode_init_once);

  static void init_once(void * foo, struct kmem_cache * cachep, unsigned long flags)

  {
  	struct inode * inode = (struct inode *) foo;
  
  	if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
  	    SLAB_CTOR_CONSTRUCTOR)
  		inode_init_once(inode);
  }
  
  /*
   * inode_lock must be held
   */
  void __iget(struct inode * inode)
  {
  	if (atomic_read(&inode->i_count)) {
  		atomic_inc(&inode->i_count);
  		return;
  	}
  	atomic_inc(&inode->i_count);
  	if (!(inode->i_state & (I_DIRTY|I_LOCK)))
  		list_move(&inode->i_list, &inode_in_use);
  	inodes_stat.nr_unused--;
  }
  
  /**
   * clear_inode - clear an inode
   * @inode: inode to clear
   *
   * This is called by the filesystem to tell us
   * that the inode is no longer useful. We just
   * terminate it with extreme prejudice.
   */
  void clear_inode(struct inode *inode)
  {
  	might_sleep();
  	invalidate_inode_buffers(inode);
         

  	BUG_ON(inode->i_data.nrpages);
  	BUG_ON(!(inode->i_state & I_FREEING));
  	BUG_ON(inode->i_state & I_CLEAR);

  	wait_on_inode(inode);
  	DQUOT_DROP(inode);
  	if (inode->i_sb && inode->i_sb->s_op->clear_inode)
  		inode->i_sb->s_op->clear_inode(inode);

  	if (S_ISBLK(inode->i_mode) && inode->i_bdev)

  		bd_forget(inode);

  	if (S_ISCHR(inode->i_mode) && inode->i_cdev)

  		cd_forget(inode);
  	inode->i_state = I_CLEAR;
  }
  
  EXPORT_SYMBOL(clear_inode);
  
  /*
   * dispose_list - dispose of the contents of a local list
   * @head: the head of the list to free
   *
   * Dispose-list gets a local list with local inodes in it, so it doesn't
   * need to worry about list corruption and SMP locks.
   */
  static void dispose_list(struct list_head *head)
  {
  	int nr_disposed = 0;
  
  	while (!list_empty(head)) {
  		struct inode *inode;
  
  		inode = list_entry(head->next, struct inode, i_list);
  		list_del(&inode->i_list);
  
  		if (inode->i_data.nrpages)
  			truncate_inode_pages(&inode->i_data, 0);
  		clear_inode(inode);

  
  		spin_lock(&inode_lock);
  		hlist_del_init(&inode->i_hash);
  		list_del_init(&inode->i_sb_list);
  		spin_unlock(&inode_lock);
  
  		wake_up_inode(inode);

  		destroy_inode(inode);
  		nr_disposed++;
  	}
  	spin_lock(&inode_lock);
  	inodes_stat.nr_inodes -= nr_disposed;
  	spin_unlock(&inode_lock);
  }
  
  /*
   * Invalidate all inodes for a device.
   */
  static int invalidate_list(struct list_head *head, struct list_head *dispose)
  {
  	struct list_head *next;
  	int busy = 0, count = 0;
  
  	next = head->next;
  	for (;;) {
  		struct list_head * tmp = next;
  		struct inode * inode;
  
  		/*
  		 * We can reschedule here without worrying about the list's
  		 * consistency because the per-sb list of inodes must not

  		 * change during umount anymore, and because iprune_mutex keeps

  		 * shrink_icache_memory() away.
  		 */
  		cond_resched_lock(&inode_lock);
  
  		next = next->next;
  		if (tmp == head)
  			break;
  		inode = list_entry(tmp, struct inode, i_sb_list);
  		invalidate_inode_buffers(inode);
  		if (!atomic_read(&inode->i_count)) {

  			list_move(&inode->i_list, dispose);
  			inode->i_state |= I_FREEING;
  			count++;
  			continue;
  		}
  		busy = 1;
  	}
  	/* only unused inodes may be cached with i_count zero */
  	inodes_stat.nr_unused -= count;
  	return busy;
  }

  /**
   *	invalidate_inodes	- discard the inodes on a device
   *	@sb: superblock
   *
   *	Discard all of the inodes for a given superblock. If the discard
   *	fails because there are busy inodes then a non zero value is returned.
   *	If the discard is successful all the inodes have been discarded.
   */
  int invalidate_inodes(struct super_block * sb)
  {
  	int busy;
  	LIST_HEAD(throw_away);

  	mutex_lock(&iprune_mutex);

  	spin_lock(&inode_lock);

  	inotify_unmount_inodes(&sb->s_inodes);

  	busy = invalidate_list(&sb->s_inodes, &throw_away);
  	spin_unlock(&inode_lock);
  
  	dispose_list(&throw_away);

  	mutex_unlock(&iprune_mutex);

  
  	return busy;
  }
  
  EXPORT_SYMBOL(invalidate_inodes);

  
  static int can_unuse(struct inode *inode)
  {
  	if (inode->i_state)
  		return 0;
  	if (inode_has_buffers(inode))
  		return 0;
  	if (atomic_read(&inode->i_count))
  		return 0;
  	if (inode->i_data.nrpages)
  		return 0;
  	return 1;
  }
  
  /*
   * Scan `goal' inodes on the unused list for freeable ones. They are moved to
   * a temporary list and then are freed outside inode_lock by dispose_list().
   *
   * Any inodes which are pinned purely because of attached pagecache have their
   * pagecache removed.  We expect the final iput() on that inode to add it to
   * the front of the inode_unused list.  So look for it there and if the
   * inode is still freeable, proceed.  The right inode is found 99.9% of the
   * time in testing on a 4-way.
   *
   * If the inode has metadata buffers attached to mapping->private_list then
   * try to remove them.
   */
  static void prune_icache(int nr_to_scan)
  {
  	LIST_HEAD(freeable);
  	int nr_pruned = 0;
  	int nr_scanned;
  	unsigned long reap = 0;

  	mutex_lock(&iprune_mutex);

  	spin_lock(&inode_lock);
  	for (nr_scanned = 0; nr_scanned < nr_to_scan; nr_scanned++) {
  		struct inode *inode;
  
  		if (list_empty(&inode_unused))
  			break;
  
  		inode = list_entry(inode_unused.prev, struct inode, i_list);
  
  		if (inode->i_state || atomic_read(&inode->i_count)) {
  			list_move(&inode->i_list, &inode_unused);
  			continue;
  		}
  		if (inode_has_buffers(inode) || inode->i_data.nrpages) {
  			__iget(inode);
  			spin_unlock(&inode_lock);
  			if (remove_inode_buffers(inode))

  				reap += invalidate_mapping_pages(&inode->i_data,
  								0, -1);

  			iput(inode);
  			spin_lock(&inode_lock);
  
  			if (inode != list_entry(inode_unused.next,
  						struct inode, i_list))
  				continue;	/* wrong inode or list_empty */
  			if (!can_unuse(inode))
  				continue;
  		}

  		list_move(&inode->i_list, &freeable);
  		inode->i_state |= I_FREEING;
  		nr_pruned++;
  	}
  	inodes_stat.nr_unused -= nr_pruned;

  	if (current_is_kswapd())
  		__count_vm_events(KSWAPD_INODESTEAL, reap);
  	else
  		__count_vm_events(PGINODESTEAL, reap);

  	spin_unlock(&inode_lock);
  
  	dispose_list(&freeable);

  	mutex_unlock(&iprune_mutex);

  }
  
  /*
   * shrink_icache_memory() will attempt to reclaim some unused inodes.  Here,
   * "unused" means that no dentries are referring to the inodes: the files are
   * not open and the dcache references to those inodes have already been
   * reclaimed.
   *
   * This function is passed the number of inodes to scan, and it returns the
   * total number of remaining possibly-reclaimable inodes.
   */

  static int shrink_icache_memory(int nr, gfp_t gfp_mask)

  {
  	if (nr) {
  		/*
  		 * Nasty deadlock avoidance.  We may hold various FS locks,
  		 * and we don't want to recurse into the FS that called us
  		 * in clear_inode() and friends..
  	 	 */
  		if (!(gfp_mask & __GFP_FS))
  			return -1;
  		prune_icache(nr);
  	}
  	return (inodes_stat.nr_unused / 100) * sysctl_vfs_cache_pressure;
  }
  
  static void __wait_on_freeing_inode(struct inode *inode);
  /*
   * Called with the inode lock held.
   * NOTE: we are not increasing the inode-refcount, you must call __iget()
   * by hand after calling find_inode now! This simplifies iunique and won't
   * add any additional branch in the common code.
   */
  static struct inode * find_inode(struct super_block * sb, struct hlist_head *head, int (*test)(struct inode *, void *), void *data)
  {
  	struct hlist_node *node;
  	struct inode * inode = NULL;
  
  repeat:
  	hlist_for_each (node, head) { 
  		inode = hlist_entry(node, struct inode, i_hash);
  		if (inode->i_sb != sb)
  			continue;
  		if (!test(inode, data))
  			continue;

  		if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE)) {

  			__wait_on_freeing_inode(inode);
  			goto repeat;
  		}
  		break;
  	}
  	return node ? inode : NULL;
  }
  
  /*
   * find_inode_fast is the fast path version of find_inode, see the comment at
   * iget_locked for details.
   */
  static struct inode * find_inode_fast(struct super_block * sb, struct hlist_head *head, unsigned long ino)
  {
  	struct hlist_node *node;
  	struct inode * inode = NULL;
  
  repeat:
  	hlist_for_each (node, head) {
  		inode = hlist_entry(node, struct inode, i_hash);
  		if (inode->i_ino != ino)
  			continue;
  		if (inode->i_sb != sb)
  			continue;

  		if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE)) {

  			__wait_on_freeing_inode(inode);
  			goto repeat;
  		}
  		break;
  	}
  	return node ? inode : NULL;
  }
  
  /**
   *	new_inode 	- obtain an inode
   *	@sb: superblock
   *
   *	Allocates a new inode for given superblock.
   */
  struct inode *new_inode(struct super_block *sb)
  {
  	static unsigned long last_ino;
  	struct inode * inode;
  
  	spin_lock_prefetch(&inode_lock);
  	
  	inode = alloc_inode(sb);
  	if (inode) {
  		spin_lock(&inode_lock);
  		inodes_stat.nr_inodes++;
  		list_add(&inode->i_list, &inode_in_use);
  		list_add(&inode->i_sb_list, &sb->s_inodes);
  		inode->i_ino = ++last_ino;
  		inode->i_state = 0;
  		spin_unlock(&inode_lock);
  	}
  	return inode;
  }
  
  EXPORT_SYMBOL(new_inode);
  
  void unlock_new_inode(struct inode *inode)
  {
  	/*
  	 * This is special!  We do not need the spinlock
  	 * when clearing I_LOCK, because we're guaranteed
  	 * that nobody else tries to do anything about the
  	 * state of the inode when it is locked, as we
  	 * just created it (so there can be no old holders
  	 * that haven't tested I_LOCK).
  	 */
  	inode->i_state &= ~(I_LOCK|I_NEW);
  	wake_up_inode(inode);
  }
  
  EXPORT_SYMBOL(unlock_new_inode);
  
  /*
   * This is called without the inode lock held.. Be careful.
   *
   * We no longer cache the sb_flags in i_flags - see fs.h
   *	-- rmk@arm.uk.linux.org
   */
  static struct inode * get_new_inode(struct super_block *sb, struct hlist_head *head, int (*test)(struct inode *, void *), int (*set)(struct inode *, void *), void *data)
  {
  	struct inode * inode;
  
  	inode = alloc_inode(sb);
  	if (inode) {
  		struct inode * old;
  
  		spin_lock(&inode_lock);
  		/* We released the lock, so.. */
  		old = find_inode(sb, head, test, data);
  		if (!old) {
  			if (set(inode, data))
  				goto set_failed;
  
  			inodes_stat.nr_inodes++;
  			list_add(&inode->i_list, &inode_in_use);
  			list_add(&inode->i_sb_list, &sb->s_inodes);
  			hlist_add_head(&inode->i_hash, head);
  			inode->i_state = I_LOCK|I_NEW;
  			spin_unlock(&inode_lock);
  
  			/* Return the locked inode with I_NEW set, the
  			 * caller is responsible for filling in the contents
  			 */
  			return inode;
  		}
  
  		/*
  		 * Uhhuh, somebody else created the same inode under
  		 * us. Use the old inode instead of the one we just
  		 * allocated.
  		 */
  		__iget(old);
  		spin_unlock(&inode_lock);
  		destroy_inode(inode);
  		inode = old;
  		wait_on_inode(inode);
  	}
  	return inode;
  
  set_failed:
  	spin_unlock(&inode_lock);
  	destroy_inode(inode);
  	return NULL;
  }
  
  /*
   * get_new_inode_fast is the fast path version of get_new_inode, see the
   * comment at iget_locked for details.
   */
  static struct inode * get_new_inode_fast(struct super_block *sb, struct hlist_head *head, unsigned long ino)
  {
  	struct inode * inode;
  
  	inode = alloc_inode(sb);
  	if (inode) {
  		struct inode * old;
  
  		spin_lock(&inode_lock);
  		/* We released the lock, so.. */
  		old = find_inode_fast(sb, head, ino);
  		if (!old) {
  			inode->i_ino = ino;
  			inodes_stat.nr_inodes++;
  			list_add(&inode->i_list, &inode_in_use);
  			list_add(&inode->i_sb_list, &sb->s_inodes);
  			hlist_add_head(&inode->i_hash, head);
  			inode->i_state = I_LOCK|I_NEW;
  			spin_unlock(&inode_lock);
  
  			/* Return the locked inode with I_NEW set, the
  			 * caller is responsible for filling in the contents
  			 */
  			return inode;
  		}
  
  		/*
  		 * Uhhuh, somebody else created the same inode under
  		 * us. Use the old inode instead of the one we just
  		 * allocated.
  		 */
  		__iget(old);
  		spin_unlock(&inode_lock);
  		destroy_inode(inode);
  		inode = old;
  		wait_on_inode(inode);
  	}
  	return inode;
  }

  static unsigned long hash(struct super_block *sb, unsigned long hashval)

  {
  	unsigned long tmp;
  
  	tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) /
  			L1_CACHE_BYTES;
  	tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> I_HASHBITS);
  	return tmp & I_HASHMASK;
  }
  
  /**
   *	iunique - get a unique inode number
   *	@sb: superblock
   *	@max_reserved: highest reserved inode number
   *
   *	Obtain an inode number that is unique on the system for a given
   *	superblock. This is used by file systems that have no natural
   *	permanent inode numbering system. An inode number is returned that
   *	is higher than the reserved limit but unique.
   *
   *	BUGS:
   *	With a large number of inodes live on the file system this function
   *	currently becomes quite slow.
   */
  ino_t iunique(struct super_block *sb, ino_t max_reserved)
  {
  	static ino_t counter;
  	struct inode *inode;
  	struct hlist_head * head;
  	ino_t res;
  	spin_lock(&inode_lock);
  retry:
  	if (counter > max_reserved) {
  		head = inode_hashtable + hash(sb,counter);
  		res = counter++;
  		inode = find_inode_fast(sb, head, res);
  		if (!inode) {
  			spin_unlock(&inode_lock);
  			return res;
  		}
  	} else {
  		counter = max_reserved + 1;
  	}
  	goto retry;
  	
  }
  
  EXPORT_SYMBOL(iunique);
  
  struct inode *igrab(struct inode *inode)
  {
  	spin_lock(&inode_lock);

  	if (!(inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE)))

  		__iget(inode);
  	else
  		/*
  		 * Handle the case where s_op->clear_inode is not been
  		 * called yet, and somebody is calling igrab
  		 * while the inode is getting freed.
  		 */
  		inode = NULL;
  	spin_unlock(&inode_lock);
  	return inode;
  }
  
  EXPORT_SYMBOL(igrab);
  
  /**
   * ifind - internal function, you want ilookup5() or iget5().
   * @sb:		super block of file system to search
   * @head:       the head of the list to search
   * @test:	callback used for comparisons between inodes
   * @data:	opaque data pointer to pass to @test

   * @wait:	if true wait for the inode to be unlocked, if false do not

   *
   * ifind() searches for the inode specified by @data in the inode
   * cache. This is a generalized version of ifind_fast() for file systems where
   * the inode number is not sufficient for unique identification of an inode.
   *
   * If the inode is in the cache, the inode is returned with an incremented
   * reference count.
   *
   * Otherwise NULL is returned.
   *
   * Note, @test is called with the inode_lock held, so can't sleep.
   */

  static struct inode *ifind(struct super_block *sb,

  		struct hlist_head *head, int (*test)(struct inode *, void *),

  		void *data, const int wait)

  {
  	struct inode *inode;
  
  	spin_lock(&inode_lock);
  	inode = find_inode(sb, head, test, data);
  	if (inode) {
  		__iget(inode);
  		spin_unlock(&inode_lock);

  		if (likely(wait))
  			wait_on_inode(inode);

  		return inode;
  	}
  	spin_unlock(&inode_lock);
  	return NULL;
  }
  
  /**
   * ifind_fast - internal function, you want ilookup() or iget().
   * @sb:		super block of file system to search
   * @head:       head of the list to search
   * @ino:	inode number to search for
   *
   * ifind_fast() searches for the inode @ino in the inode cache. This is for
   * file systems where the inode number is sufficient for unique identification
   * of an inode.
   *
   * If the inode is in the cache, the inode is returned with an incremented
   * reference count.
   *
   * Otherwise NULL is returned.
   */

  static struct inode *ifind_fast(struct super_block *sb,

  		struct hlist_head *head, unsigned long ino)
  {
  	struct inode *inode;
  
  	spin_lock(&inode_lock);
  	inode = find_inode_fast(sb, head, ino);
  	if (inode) {
  		__iget(inode);
  		spin_unlock(&inode_lock);
  		wait_on_inode(inode);
  		return inode;
  	}
  	spin_unlock(&inode_lock);
  	return NULL;
  }
  
  /**

   * ilookup5_nowait - search for an inode in the inode cache

   * @sb:		super block of file system to search
   * @hashval:	hash value (usually inode number) to search for
   * @test:	callback used for comparisons between inodes
   * @data:	opaque data pointer to pass to @test
   *
   * ilookup5() uses ifind() to search for the inode specified by @hashval and
   * @data in the inode cache. This is a generalized version of ilookup() for
   * file systems where the inode number is not sufficient for unique
   * identification of an inode.
   *
   * If the inode is in the cache, the inode is returned with an incremented

   * reference count.  Note, the inode lock is not waited upon so you have to be
   * very careful what you do with the returned inode.  You probably should be
   * using ilookup5() instead.
   *
   * Otherwise NULL is returned.
   *
   * Note, @test is called with the inode_lock held, so can't sleep.
   */
  struct inode *ilookup5_nowait(struct super_block *sb, unsigned long hashval,
  		int (*test)(struct inode *, void *), void *data)
  {
  	struct hlist_head *head = inode_hashtable + hash(sb, hashval);
  
  	return ifind(sb, head, test, data, 0);
  }
  
  EXPORT_SYMBOL(ilookup5_nowait);
  
  /**
   * ilookup5 - search for an inode in the inode cache
   * @sb:		super block of file system to search
   * @hashval:	hash value (usually inode number) to search for
   * @test:	callback used for comparisons between inodes
   * @data:	opaque data pointer to pass to @test
   *
   * ilookup5() uses ifind() to search for the inode specified by @hashval and
   * @data in the inode cache. This is a generalized version of ilookup() for
   * file systems where the inode number is not sufficient for unique
   * identification of an inode.
   *
   * If the inode is in the cache, the inode lock is waited upon and the inode is
   * returned with an incremented reference count.

   *
   * Otherwise NULL is returned.
   *
   * Note, @test is called with the inode_lock held, so can't sleep.
   */
  struct inode *ilookup5(struct super_block *sb, unsigned long hashval,
  		int (*test)(struct inode *, void *), void *data)
  {
  	struct hlist_head *head = inode_hashtable + hash(sb, hashval);

  	return ifind(sb, head, test, data, 1);

  }
  
  EXPORT_SYMBOL(ilookup5);
  
  /**
   * ilookup - search for an inode in the inode cache
   * @sb:		super block of file system to search
   * @ino:	inode number to search for
   *
   * ilookup() uses ifind_fast() to search for the inode @ino in the inode cache.
   * This is for file systems where the inode number is sufficient for unique
   * identification of an inode.
   *
   * If the inode is in the cache, the inode is returned with an incremented
   * reference count.
   *
   * Otherwise NULL is returned.
   */
  struct inode *ilookup(struct super_block *sb, unsigned long ino)
  {
  	struct hlist_head *head = inode_hashtable + hash(sb, ino);
  
  	return ifind_fast(sb, head, ino);
  }
  
  EXPORT_SYMBOL(ilookup);
  
  /**
   * iget5_locked - obtain an inode from a mounted file system
   * @sb:		super block of file system
   * @hashval:	hash value (usually inode number) to get
   * @test:	callback used for comparisons between inodes
   * @set:	callback used to initialize a new struct inode
   * @data:	opaque data pointer to pass to @test and @set
   *
   * This is iget() without the read_inode() portion of get_new_inode().
   *
   * iget5_locked() uses ifind() to search for the inode specified by @hashval
   * and @data in the inode cache and if present it is returned with an increased
   * reference count. This is a generalized version of iget_locked() for file
   * systems where the inode number is not sufficient for unique identification
   * of an inode.
   *
   * If the inode is not in cache, get_new_inode() is called to allocate a new
   * inode and this is returned locked, hashed, and with the I_NEW flag set. The
   * file system gets to fill it in before unlocking it via unlock_new_inode().
   *
   * Note both @test and @set are called with the inode_lock held, so can't sleep.
   */
  struct inode *iget5_locked(struct super_block *sb, unsigned long hashval,
  		int (*test)(struct inode *, void *),
  		int (*set)(struct inode *, void *), void *data)
  {
  	struct hlist_head *head = inode_hashtable + hash(sb, hashval);
  	struct inode *inode;

  	inode = ifind(sb, head, test, data, 1);

  	if (inode)
  		return inode;
  	/*
  	 * get_new_inode() will do the right thing, re-trying the search
  	 * in case it had to block at any point.
  	 */
  	return get_new_inode(sb, head, test, set, data);
  }
  
  EXPORT_SYMBOL(iget5_locked);
  
  /**
   * iget_locked - obtain an inode from a mounted file system
   * @sb:		super block of file system
   * @ino:	inode number to get
   *
   * This is iget() without the read_inode() portion of get_new_inode_fast().
   *
   * iget_locked() uses ifind_fast() to search for the inode specified by @ino in
   * the inode cache and if present it is returned with an increased reference
   * count. This is for file systems where the inode number is sufficient for
   * unique identification of an inode.
   *
   * If the inode is not in cache, get_new_inode_fast() is called to allocate a
   * new inode and this is returned locked, hashed, and with the I_NEW flag set.
   * The file system gets to fill it in before unlocking it via
   * unlock_new_inode().
   */
  struct inode *iget_locked(struct super_block *sb, unsigned long ino)
  {
  	struct hlist_head *head = inode_hashtable + hash(sb, ino);
  	struct inode *inode;
  
  	inode = ifind_fast(sb, head, ino);
  	if (inode)
  		return inode;
  	/*
  	 * get_new_inode_fast() will do the right thing, re-trying the search
  	 * in case it had to block at any point.
  	 */
  	return get_new_inode_fast(sb, head, ino);
  }
  
  EXPORT_SYMBOL(iget_locked);
  
  /**
   *	__insert_inode_hash - hash an inode
   *	@inode: unhashed inode
   *	@hashval: unsigned long value used to locate this object in the
   *		inode_hashtable.
   *
   *	Add an inode to the inode hash for this superblock.
   */
  void __insert_inode_hash(struct inode *inode, unsigned long hashval)
  {
  	struct hlist_head *head = inode_hashtable + hash(inode->i_sb, hashval);
  	spin_lock(&inode_lock);
  	hlist_add_head(&inode->i_hash, head);
  	spin_unlock(&inode_lock);
  }
  
  EXPORT_SYMBOL(__insert_inode_hash);
  
  /**
   *	remove_inode_hash - remove an inode from the hash
   *	@inode: inode to unhash
   *
   *	Remove an inode from the superblock.
   */
  void remove_inode_hash(struct inode *inode)
  {
  	spin_lock(&inode_lock);
  	hlist_del_init(&inode->i_hash);
  	spin_unlock(&inode_lock);
  }
  
  EXPORT_SYMBOL(remove_inode_hash);
  
  /*
   * Tell the filesystem that this inode is no longer of any interest and should
   * be completely destroyed.
   *
   * We leave the inode in the inode hash table until *after* the filesystem's
   * ->delete_inode completes.  This ensures that an iget (such as nfsd might
   * instigate) will always find up-to-date information either in the hash or on
   * disk.
   *
   * I_FREEING is set so that no-one will take a new reference to the inode while
   * it is being deleted.
   */
  void generic_delete_inode(struct inode *inode)
  {

  	const struct super_operations *op = inode->i_sb->s_op;

  
  	list_del_init(&inode->i_list);
  	list_del_init(&inode->i_sb_list);

  	inode->i_state |= I_FREEING;

  	inodes_stat.nr_inodes--;
  	spin_unlock(&inode_lock);

  	security_inode_delete(inode);
  
  	if (op->delete_inode) {
  		void (*delete)(struct inode *) = op->delete_inode;
  		if (!is_bad_inode(inode))
  			DQUOT_INIT(inode);

  		/* Filesystems implementing their own
  		 * s_op->delete_inode are required to call
  		 * truncate_inode_pages and clear_inode()
  		 * internally */

  		delete(inode);

  	} else {
  		truncate_inode_pages(&inode->i_data, 0);

  		clear_inode(inode);

  	}

  	spin_lock(&inode_lock);
  	hlist_del_init(&inode->i_hash);
  	spin_unlock(&inode_lock);
  	wake_up_inode(inode);

  	BUG_ON(inode->i_state != I_CLEAR);

  	destroy_inode(inode);
  }
  
  EXPORT_SYMBOL(generic_delete_inode);
  
  static void generic_forget_inode(struct inode *inode)
  {
  	struct super_block *sb = inode->i_sb;
  
  	if (!hlist_unhashed(&inode->i_hash)) {
  		if (!(inode->i_state & (I_DIRTY|I_LOCK)))
  			list_move(&inode->i_list, &inode_unused);
  		inodes_stat.nr_unused++;

  		if (!sb || (sb->s_flags & MS_ACTIVE)) {
  			spin_unlock(&inode_lock);

  			return;

  		}
  		inode->i_state |= I_WILL_FREE;
  		spin_unlock(&inode_lock);

  		write_inode_now(inode, 1);
  		spin_lock(&inode_lock);

  		inode->i_state &= ~I_WILL_FREE;

  		inodes_stat.nr_unused--;
  		hlist_del_init(&inode->i_hash);
  	}
  	list_del_init(&inode->i_list);
  	list_del_init(&inode->i_sb_list);

  	inode->i_state |= I_FREEING;

  	inodes_stat.nr_inodes--;
  	spin_unlock(&inode_lock);
  	if (inode->i_data.nrpages)
  		truncate_inode_pages(&inode->i_data, 0);
  	clear_inode(inode);

  	wake_up_inode(inode);

  	destroy_inode(inode);
  }
  
  /*
   * Normal UNIX filesystem behaviour: delete the
   * inode when the usage count drops to zero, and
   * i_nlink is zero.
   */

  void generic_drop_inode(struct inode *inode)

  {
  	if (!inode->i_nlink)
  		generic_delete_inode(inode);
  	else
  		generic_forget_inode(inode);
  }

  EXPORT_SYMBOL_GPL(generic_drop_inode);

  /*
   * Called when we're dropping the last reference
   * to an inode. 
   *
   * Call the FS "drop()" function, defaulting to
   * the legacy UNIX filesystem behaviour..
   *
   * NOTE! NOTE! NOTE! We're called with the inode lock
   * held, and the drop function is supposed to release
   * the lock!
   */
  static inline void iput_final(struct inode *inode)
  {

  	const struct super_operations *op = inode->i_sb->s_op;

  	void (*drop)(struct inode *) = generic_drop_inode;
  
  	if (op && op->drop_inode)
  		drop = op->drop_inode;
  	drop(inode);
  }
  
  /**
   *	iput	- put an inode 
   *	@inode: inode to put
   *
   *	Puts an inode, dropping its usage count. If the inode use count hits
   *	zero, the inode is then freed and may also be destroyed.
   *
   *	Consequently, iput() can sleep.
   */
  void iput(struct inode *inode)
  {
  	if (inode) {

  		const struct super_operations *op = inode->i_sb->s_op;

  
  		BUG_ON(inode->i_state == I_CLEAR);
  
  		if (op && op->put_inode)
  			op->put_inode(inode);
  
  		if (atomic_dec_and_lock(&inode->i_count, &inode_lock))
  			iput_final(inode);
  	}
  }
  
  EXPORT_SYMBOL(iput);
  
  /**
   *	bmap	- find a block number in a file
   *	@inode: inode of file
   *	@block: block to find
   *
   *	Returns the block number on the device holding the inode that
   *	is the disk block number for the block of the file requested.
   *	That is, asked for block 4 of inode 1 the function will return the
   *	disk block relative to the disk start that holds that block of the 
   *	file.
   */
  sector_t bmap(struct inode * inode, sector_t block)
  {
  	sector_t res = 0;
  	if (inode->i_mapping->a_ops->bmap)
  		res = inode->i_mapping->a_ops->bmap(inode->i_mapping, block);
  	return res;
  }

  EXPORT_SYMBOL(bmap);
  
  /**

   *	touch_atime	-	update the access time
   *	@mnt: mount the inode is accessed on

   *	@dentry: dentry accessed

   *
   *	Update the accessed time on an inode and mark it for writeback.
   *	This function automatically handles read only file systems and media,
   *	as well as the "noatime" flag and inode specific "noatime" markers.
   */

  void touch_atime(struct vfsmount *mnt, struct dentry *dentry)

  {

  	struct inode *inode = dentry->d_inode;

  	struct timespec now;

  	if (inode->i_flags & S_NOATIME)
  		return;

  	if (IS_NOATIME(inode))

  		return;
  	if ((inode->i_sb->s_flags & MS_NODIRATIME) && S_ISDIR(inode->i_mode))

  		return;

  
  	/*
  	 * We may have a NULL vfsmount when coming from NFSD
  	 */

  	if (mnt) {
  		if (mnt->mnt_flags & MNT_NOATIME)
  			return;
  		if ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode))
  			return;

  
  		if (mnt->mnt_flags & MNT_RELATIME) {
  			/*
  			 * With relative atime, only update atime if the
  			 * previous atime is earlier than either the ctime or
  			 * mtime.
  			 */
  			if (timespec_compare(&inode->i_mtime,
  						&inode->i_atime) < 0 &&
  			    timespec_compare(&inode->i_ctime,
  						&inode->i_atime) < 0)
  				return;
  		}

  	}

  
  	now = current_fs_time(inode->i_sb);

  	if (timespec_equal(&inode->i_atime, &now))
  		return;
  
  	inode->i_atime = now;
  	mark_inode_dirty_sync(inode);

  }

  EXPORT_SYMBOL(touch_atime);

  
  /**

   *	file_update_time	-	update mtime and ctime time
   *	@file: file accessed

   *

   *	Update the mtime and ctime members of an inode and mark the inode
   *	for writeback.  Note that this function is meant exclusively for
   *	usage in the file write path of filesystems, and filesystems may
   *	choose to explicitly ignore update via this function with the
   *	S_NOCTIME inode flag, e.g. for network filesystem where these
   *	timestamps are handled by the server.

   */

  void file_update_time(struct file *file)

  {

  	struct inode *inode = file->f_path.dentry->d_inode;

  	struct timespec now;
  	int sync_it = 0;
  
  	if (IS_NOCMTIME(inode))
  		return;
  	if (IS_RDONLY(inode))
  		return;
  
  	now = current_fs_time(inode->i_sb);

  	if (!timespec_equal(&inode->i_mtime, &now)) {
  		inode->i_mtime = now;

  		sync_it = 1;

  	}

  	if (!timespec_equal(&inode->i_ctime, &now)) {
  		inode->i_ctime = now;

  		sync_it = 1;

  	}

  	if (sync_it)
  		mark_inode_dirty_sync(inode);
  }

  EXPORT_SYMBOL(file_update_time);

  
  int inode_needs_sync(struct inode *inode)
  {
  	if (IS_SYNC(inode))
  		return 1;
  	if (S_ISDIR(inode->i_mode) && IS_DIRSYNC(inode))
  		return 1;
  	return 0;
  }
  
  EXPORT_SYMBOL(inode_needs_sync);

  int inode_wait(void *word)
  {
  	schedule();
  	return 0;
  }
  
  /*

   * If we try to find an inode in the inode hash while it is being
   * deleted, we have to wait until the filesystem completes its
   * deletion before reporting that it isn't found.  This function waits
   * until the deletion _might_ have completed.  Callers are responsible
   * to recheck inode state.
   *
   * It doesn't matter if I_LOCK is not set initially, a call to
   * wake_up_inode() after removing from the hash list will DTRT.
   *

   * This is called with inode_lock held.
   */
  static void __wait_on_freeing_inode(struct inode *inode)
  {
  	wait_queue_head_t *wq;
  	DEFINE_WAIT_BIT(wait, &inode->i_state, __I_LOCK);

  	wq = bit_waitqueue(&inode->i_state, __I_LOCK);
  	prepare_to_wait(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
  	spin_unlock(&inode_lock);
  	schedule();
  	finish_wait(wq, &wait.wait);
  	spin_lock(&inode_lock);
  }
  
  void wake_up_inode(struct inode *inode)
  {
  	/*
  	 * Prevent speculative execution through spin_unlock(&inode_lock);
  	 */
  	smp_mb();
  	wake_up_bit(&inode->i_state, __I_LOCK);
  }

  /*
   * We rarely want to lock two inodes that do not have a parent/child
   * relationship (such as directory, child inode) simultaneously. The
   * vast majority of file systems should be able to get along fine
   * without this. Do not use these functions except as a last resort.
   */
  void inode_double_lock(struct inode *inode1, struct inode *inode2)
  {
  	if (inode1 == NULL || inode2 == NULL || inode1 == inode2) {
  		if (inode1)
  			mutex_lock(&inode1->i_mutex);
  		else if (inode2)
  			mutex_lock(&inode2->i_mutex);
  		return;
  	}
  
  	if (inode1 < inode2) {
  		mutex_lock_nested(&inode1->i_mutex, I_MUTEX_PARENT);
  		mutex_lock_nested(&inode2->i_mutex, I_MUTEX_CHILD);
  	} else {
  		mutex_lock_nested(&inode2->i_mutex, I_MUTEX_PARENT);
  		mutex_lock_nested(&inode1->i_mutex, I_MUTEX_CHILD);
  	}
  }
  EXPORT_SYMBOL(inode_double_lock);
  
  void inode_double_unlock(struct inode *inode1, struct inode *inode2)
  {
  	if (inode1)
  		mutex_unlock(&inode1->i_mutex);
  
  	if (inode2 && inode2 != inode1)
  		mutex_unlock(&inode2->i_mutex);
  }
  EXPORT_SYMBOL(inode_double_unlock);

  static __initdata unsigned long ihash_entries;
  static int __init set_ihash_entries(char *str)
  {
  	if (!str)
  		return 0;
  	ihash_entries = simple_strtoul(str, &str, 0);
  	return 1;
  }
  __setup("ihash_entries=", set_ihash_entries);
  
  /*
   * Initialize the waitqueues and inode hash table.
   */
  void __init inode_init_early(void)
  {
  	int loop;
  
  	/* If hashes are distributed across NUMA nodes, defer
  	 * hash allocation until vmalloc space is available.
  	 */
  	if (hashdist)
  		return;
  
  	inode_hashtable =
  		alloc_large_system_hash("Inode-cache",
  					sizeof(struct hlist_head),
  					ihash_entries,
  					14,
  					HASH_EARLY,
  					&i_hash_shift,
  					&i_hash_mask,
  					0);
  
  	for (loop = 0; loop < (1 << i_hash_shift); loop++)
  		INIT_HLIST_HEAD(&inode_hashtable[loop]);
  }
  
  void __init inode_init(unsigned long mempages)
  {
  	int loop;
  
  	/* inode slab cache */

  	inode_cachep = kmem_cache_create("inode_cache",
  					 sizeof(struct inode),
  					 0,
  					 (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
  					 SLAB_MEM_SPREAD),
  					 init_once,
  					 NULL);

  	set_shrinker(DEFAULT_SEEKS, shrink_icache_memory);
  
  	/* Hash may have been set up in inode_init_early */
  	if (!hashdist)
  		return;
  
  	inode_hashtable =
  		alloc_large_system_hash("Inode-cache",
  					sizeof(struct hlist_head),
  					ihash_entries,
  					14,
  					0,
  					&i_hash_shift,
  					&i_hash_mask,
  					0);
  
  	for (loop = 0; loop < (1 << i_hash_shift); loop++)
  		INIT_HLIST_HEAD(&inode_hashtable[loop]);
  }
  
  void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev)
  {
  	inode->i_mode = mode;
  	if (S_ISCHR(mode)) {
  		inode->i_fop = &def_chr_fops;
  		inode->i_rdev = rdev;
  	} else if (S_ISBLK(mode)) {
  		inode->i_fop = &def_blk_fops;
  		inode->i_rdev = rdev;
  	} else if (S_ISFIFO(mode))
  		inode->i_fop = &def_fifo_fops;
  	else if (S_ISSOCK(mode))
  		inode->i_fop = &bad_sock_fops;
  	else
  		printk(KERN_DEBUG "init_special_inode: bogus i_mode (%o)
  ",
  		       mode);
  }
  EXPORT_SYMBOL(init_special_inode);