/*
   * fs/dcache.c
   *
   * Complete reimplementation
   * (C) 1997 Thomas Schoebel-Theuer,
   * with heavy changes by Linus Torvalds
   */
  
  /*
   * Notes on the allocation strategy:
   *
   * The dcache is a master of the icache - whenever a dcache entry
   * exists, the inode will always exist. "iput()" is done either when
   * the dcache entry is deleted or garbage collected.
   */

  #include <linux/syscalls.h>
  #include <linux/string.h>
  #include <linux/mm.h>
  #include <linux/fs.h>

  #include <linux/fsnotify.h>

  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/smp_lock.h>
  #include <linux/hash.h>
  #include <linux/cache.h>
  #include <linux/module.h>
  #include <linux/mount.h>
  #include <linux/file.h>
  #include <asm/uaccess.h>
  #include <linux/security.h>
  #include <linux/seqlock.h>
  #include <linux/swap.h>
  #include <linux/bootmem.h>

  #include "internal.h"

  int sysctl_vfs_cache_pressure __read_mostly = 100;

  EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
  
   __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lock);

  static __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);

  
  EXPORT_SYMBOL(dcache_lock);

  static struct kmem_cache *dentry_cache __read_mostly;

  
  #define DNAME_INLINE_LEN (sizeof(struct dentry)-offsetof(struct dentry,d_iname))
  
  /*
   * This is the single most critical data structure when it comes
   * to the dcache: the hashtable for lookups. Somebody should try
   * to make this good - I've just made it work.
   *
   * This hash-function tries to avoid losing too many bits of hash
   * information, yet avoid using a prime hash-size or similar.
   */
  #define D_HASHBITS     d_hash_shift
  #define D_HASHMASK     d_hash_mask

  static unsigned int d_hash_mask __read_mostly;
  static unsigned int d_hash_shift __read_mostly;
  static struct hlist_head *dentry_hashtable __read_mostly;

  static LIST_HEAD(dentry_unused);
  
  /* Statistics gathering. */
  struct dentry_stat_t dentry_stat = {
  	.age_limit = 45,
  };

  static void __d_free(struct dentry *dentry)

  {

  	if (dname_external(dentry))
  		kfree(dentry->d_name.name);
  	kmem_cache_free(dentry_cache, dentry); 
  }

  static void d_callback(struct rcu_head *head)
  {
  	struct dentry * dentry = container_of(head, struct dentry, d_u.d_rcu);
  	__d_free(dentry);
  }

  /*
   * no dcache_lock, please.  The caller must decrement dentry_stat.nr_dentry
   * inside dcache_lock.
   */
  static void d_free(struct dentry *dentry)
  {
  	if (dentry->d_op && dentry->d_op->d_release)
  		dentry->d_op->d_release(dentry);

  	/* if dentry was never inserted into hash, immediate free is OK */
  	if (dentry->d_hash.pprev == NULL)
  		__d_free(dentry);
  	else
  		call_rcu(&dentry->d_u.d_rcu, d_callback);

  }
  
  /*
   * Release the dentry's inode, using the filesystem
   * d_iput() operation if defined.
   * Called with dcache_lock and per dentry lock held, drops both.
   */

  static void dentry_iput(struct dentry * dentry)

  {
  	struct inode *inode = dentry->d_inode;
  	if (inode) {
  		dentry->d_inode = NULL;
  		list_del_init(&dentry->d_alias);
  		spin_unlock(&dentry->d_lock);
  		spin_unlock(&dcache_lock);

  		if (!inode->i_nlink)
  			fsnotify_inoderemove(inode);

  		if (dentry->d_op && dentry->d_op->d_iput)
  			dentry->d_op->d_iput(dentry, inode);
  		else
  			iput(inode);
  	} else {
  		spin_unlock(&dentry->d_lock);
  		spin_unlock(&dcache_lock);
  	}
  }
  
  /* 
   * This is dput
   *
   * This is complicated by the fact that we do not want to put
   * dentries that are no longer on any hash chain on the unused
   * list: we'd much rather just get rid of them immediately.
   *
   * However, that implies that we have to traverse the dentry
   * tree upwards to the parents which might _also_ now be
   * scheduled for deletion (it may have been only waiting for
   * its last child to go away).
   *
   * This tail recursion is done by hand as we don't want to depend
   * on the compiler to always get this right (gcc generally doesn't).
   * Real recursion would eat up our stack space.
   */
  
  /*
   * dput - release a dentry
   * @dentry: dentry to release 
   *
   * Release a dentry. This will drop the usage count and if appropriate
   * call the dentry unlink method as well as removing it from the queues and
   * releasing its resources. If the parent dentries were scheduled for release
   * they too may now get deleted.
   *
   * no dcache lock, please.
   */
  
  void dput(struct dentry *dentry)
  {
  	if (!dentry)
  		return;
  
  repeat:
  	if (atomic_read(&dentry->d_count) == 1)
  		might_sleep();
  	if (!atomic_dec_and_lock(&dentry->d_count, &dcache_lock))
  		return;
  
  	spin_lock(&dentry->d_lock);
  	if (atomic_read(&dentry->d_count)) {
  		spin_unlock(&dentry->d_lock);
  		spin_unlock(&dcache_lock);
  		return;
  	}
  
  	/*
  	 * AV: ->d_delete() is _NOT_ allowed to block now.
  	 */
  	if (dentry->d_op && dentry->d_op->d_delete) {
  		if (dentry->d_op->d_delete(dentry))
  			goto unhash_it;
  	}
  	/* Unreachable? Get rid of it */
   	if (d_unhashed(dentry))
  		goto kill_it;
    	if (list_empty(&dentry->d_lru)) {
    		dentry->d_flags |= DCACHE_REFERENCED;
    		list_add(&dentry->d_lru, &dentry_unused);
    		dentry_stat.nr_unused++;
    	}
   	spin_unlock(&dentry->d_lock);
  	spin_unlock(&dcache_lock);
  	return;
  
  unhash_it:
  	__d_drop(dentry);
  
  kill_it: {
  		struct dentry *parent;
  
  		/* If dentry was on d_lru list
  		 * delete it from there
  		 */
    		if (!list_empty(&dentry->d_lru)) {
    			list_del(&dentry->d_lru);
    			dentry_stat.nr_unused--;
    		}

    		list_del(&dentry->d_u.d_child);

  		dentry_stat.nr_dentry--;	/* For d_free, below */
  		/*drops the locks, at that point nobody can reach this dentry */
  		dentry_iput(dentry);
  		parent = dentry->d_parent;
  		d_free(dentry);
  		if (dentry == parent)
  			return;
  		dentry = parent;
  		goto repeat;
  	}
  }
  
  /**
   * d_invalidate - invalidate a dentry
   * @dentry: dentry to invalidate
   *
   * Try to invalidate the dentry if it turns out to be
   * possible. If there are other dentries that can be
   * reached through this one we can't delete it and we
   * return -EBUSY. On success we return 0.
   *
   * no dcache lock.
   */
   
  int d_invalidate(struct dentry * dentry)
  {
  	/*
  	 * If it's already been dropped, return OK.
  	 */
  	spin_lock(&dcache_lock);
  	if (d_unhashed(dentry)) {
  		spin_unlock(&dcache_lock);
  		return 0;
  	}
  	/*
  	 * Check whether to do a partial shrink_dcache
  	 * to get rid of unused child entries.
  	 */
  	if (!list_empty(&dentry->d_subdirs)) {
  		spin_unlock(&dcache_lock);
  		shrink_dcache_parent(dentry);
  		spin_lock(&dcache_lock);
  	}
  
  	/*
  	 * Somebody else still using it?
  	 *
  	 * If it's a directory, we can't drop it
  	 * for fear of somebody re-populating it
  	 * with children (even though dropping it
  	 * would make it unreachable from the root,
  	 * we might still populate it if it was a
  	 * working directory or similar).
  	 */
  	spin_lock(&dentry->d_lock);
  	if (atomic_read(&dentry->d_count) > 1) {
  		if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) {
  			spin_unlock(&dentry->d_lock);
  			spin_unlock(&dcache_lock);
  			return -EBUSY;
  		}
  	}
  
  	__d_drop(dentry);
  	spin_unlock(&dentry->d_lock);
  	spin_unlock(&dcache_lock);
  	return 0;
  }
  
  /* This should be called _only_ with dcache_lock held */
  
  static inline struct dentry * __dget_locked(struct dentry *dentry)
  {
  	atomic_inc(&dentry->d_count);
  	if (!list_empty(&dentry->d_lru)) {
  		dentry_stat.nr_unused--;
  		list_del_init(&dentry->d_lru);
  	}
  	return dentry;
  }
  
  struct dentry * dget_locked(struct dentry *dentry)
  {
  	return __dget_locked(dentry);
  }
  
  /**
   * d_find_alias - grab a hashed alias of inode
   * @inode: inode in question
   * @want_discon:  flag, used by d_splice_alias, to request
   *          that only a DISCONNECTED alias be returned.
   *
   * If inode has a hashed alias, or is a directory and has any alias,
   * acquire the reference to alias and return it. Otherwise return NULL.
   * Notice that if inode is a directory there can be only one alias and
   * it can be unhashed only if it has no children, or if it is the root
   * of a filesystem.
   *

   * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer

   * any other hashed alias over that one unless @want_discon is set,

   * in which case only return an IS_ROOT, DCACHE_DISCONNECTED alias.

   */
  
  static struct dentry * __d_find_alias(struct inode *inode, int want_discon)
  {
  	struct list_head *head, *next, *tmp;
  	struct dentry *alias, *discon_alias=NULL;
  
  	head = &inode->i_dentry;
  	next = inode->i_dentry.next;
  	while (next != head) {
  		tmp = next;
  		next = tmp->next;
  		prefetch(next);
  		alias = list_entry(tmp, struct dentry, d_alias);
   		if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {

  			if (IS_ROOT(alias) &&
  			    (alias->d_flags & DCACHE_DISCONNECTED))

  				discon_alias = alias;
  			else if (!want_discon) {
  				__dget_locked(alias);
  				return alias;
  			}
  		}
  	}
  	if (discon_alias)
  		__dget_locked(discon_alias);
  	return discon_alias;
  }
  
  struct dentry * d_find_alias(struct inode *inode)
  {

  	struct dentry *de = NULL;
  
  	if (!list_empty(&inode->i_dentry)) {
  		spin_lock(&dcache_lock);
  		de = __d_find_alias(inode, 0);
  		spin_unlock(&dcache_lock);
  	}

  	return de;
  }
  
  /*
   *	Try to kill dentries associated with this inode.
   * WARNING: you must own a reference to inode.
   */
  void d_prune_aliases(struct inode *inode)
  {

  	struct dentry *dentry;

  restart:
  	spin_lock(&dcache_lock);

  	list_for_each_entry(dentry, &inode->i_dentry, d_alias) {

  		spin_lock(&dentry->d_lock);
  		if (!atomic_read(&dentry->d_count)) {
  			__dget_locked(dentry);
  			__d_drop(dentry);
  			spin_unlock(&dentry->d_lock);
  			spin_unlock(&dcache_lock);
  			dput(dentry);
  			goto restart;
  		}
  		spin_unlock(&dentry->d_lock);
  	}
  	spin_unlock(&dcache_lock);
  }
  
  /*

   * Throw away a dentry - free the inode, dput the parent.  This requires that
   * the LRU list has already been removed.
   *

   * Called with dcache_lock, drops it and then regains.

   * Called with dentry->d_lock held, drops it.

   */

  static void prune_one_dentry(struct dentry * dentry)

  {
  	struct dentry * parent;
  
  	__d_drop(dentry);

  	list_del(&dentry->d_u.d_child);

  	dentry_stat.nr_dentry--;	/* For d_free, below */
  	dentry_iput(dentry);
  	parent = dentry->d_parent;
  	d_free(dentry);
  	if (parent != dentry)
  		dput(parent);
  	spin_lock(&dcache_lock);
  }
  
  /**
   * prune_dcache - shrink the dcache
   * @count: number of entries to try and free

   * @sb: if given, ignore dentries for other superblocks
   *         which are being unmounted.

   *
   * Shrink the dcache. This is done when we need
   * more memory, or simply when we need to unmount
   * something (at which point we need to unuse
   * all dentries).
   *
   * This function may fail to free any resources if
   * all the dentries are in use.
   */
   

  static void prune_dcache(int count, struct super_block *sb)

  {
  	spin_lock(&dcache_lock);
  	for (; count ; count--) {
  		struct dentry *dentry;
  		struct list_head *tmp;

  		struct rw_semaphore *s_umount;

  
  		cond_resched_lock(&dcache_lock);
  
  		tmp = dentry_unused.prev;

  		if (sb) {

  			/* Try to find a dentry for this sb, but don't try
  			 * too hard, if they aren't near the tail they will
  			 * be moved down again soon
  			 */
  			int skip = count;
  			while (skip && tmp != &dentry_unused &&
  			    list_entry(tmp, struct dentry, d_lru)->d_sb != sb) {
  				skip--;
  				tmp = tmp->prev;
  			}
  		}

  		if (tmp == &dentry_unused)
  			break;
  		list_del_init(tmp);
  		prefetch(dentry_unused.prev);
   		dentry_stat.nr_unused--;
  		dentry = list_entry(tmp, struct dentry, d_lru);
  
   		spin_lock(&dentry->d_lock);
  		/*
  		 * We found an inuse dentry which was not removed from
  		 * dentry_unused because of laziness during lookup.  Do not free
  		 * it - just keep it off the dentry_unused list.
  		 */
   		if (atomic_read(&dentry->d_count)) {
   			spin_unlock(&dentry->d_lock);
  			continue;
  		}
  		/* If the dentry was recently referenced, don't free it. */
  		if (dentry->d_flags & DCACHE_REFERENCED) {
  			dentry->d_flags &= ~DCACHE_REFERENCED;
   			list_add(&dentry->d_lru, &dentry_unused);
   			dentry_stat.nr_unused++;
   			spin_unlock(&dentry->d_lock);
  			continue;
  		}

  		/*
  		 * If the dentry is not DCACHED_REFERENCED, it is time
  		 * to remove it from the dcache, provided the super block is
  		 * NULL (which means we are trying to reclaim memory)
  		 * or this dentry belongs to the same super block that
  		 * we want to shrink.
  		 */
  		/*
  		 * If this dentry is for "my" filesystem, then I can prune it
  		 * without taking the s_umount lock (I already hold it).
  		 */
  		if (sb && dentry->d_sb == sb) {
  			prune_one_dentry(dentry);
  			continue;
  		}
  		/*
  		 * ...otherwise we need to be sure this filesystem isn't being
  		 * unmounted, otherwise we could race with
  		 * generic_shutdown_super(), and end up holding a reference to
  		 * an inode while the filesystem is unmounted.
  		 * So we try to get s_umount, and make sure s_root isn't NULL.
  		 * (Take a local copy of s_umount to avoid a use-after-free of
  		 * `dentry').
  		 */
  		s_umount = &dentry->d_sb->s_umount;
  		if (down_read_trylock(s_umount)) {
  			if (dentry->d_sb->s_root != NULL) {
  				prune_one_dentry(dentry);
  				up_read(s_umount);
  				continue;
  			}
  			up_read(s_umount);
  		}
  		spin_unlock(&dentry->d_lock);

  		/*
  		 * Insert dentry at the head of the list as inserting at the
  		 * tail leads to a cycle.

  		 */

   		list_add(&dentry->d_lru, &dentry_unused);
  		dentry_stat.nr_unused++;

  	}
  	spin_unlock(&dcache_lock);
  }
  
  /*
   * Shrink the dcache for the specified super block.
   * This allows us to unmount a device without disturbing
   * the dcache for the other devices.
   *
   * This implementation makes just two traversals of the
   * unused list.  On the first pass we move the selected
   * dentries to the most recent end, and on the second
   * pass we free them.  The second pass must restart after
   * each dput(), but since the target dentries are all at
   * the end, it's really just a single traversal.
   */
  
  /**
   * shrink_dcache_sb - shrink dcache for a superblock
   * @sb: superblock
   *
   * Shrink the dcache for the specified super block. This
   * is used to free the dcache before unmounting a file
   * system
   */
  
  void shrink_dcache_sb(struct super_block * sb)
  {
  	struct list_head *tmp, *next;
  	struct dentry *dentry;
  
  	/*
  	 * Pass one ... move the dentries for the specified
  	 * superblock to the most recent end of the unused list.
  	 */
  	spin_lock(&dcache_lock);

  	list_for_each_safe(tmp, next, &dentry_unused) {

  		dentry = list_entry(tmp, struct dentry, d_lru);
  		if (dentry->d_sb != sb)
  			continue;

  		list_move(tmp, &dentry_unused);

  	}
  
  	/*
  	 * Pass two ... free the dentries for this superblock.
  	 */
  repeat:

  	list_for_each_safe(tmp, next, &dentry_unused) {

  		dentry = list_entry(tmp, struct dentry, d_lru);
  		if (dentry->d_sb != sb)
  			continue;
  		dentry_stat.nr_unused--;
  		list_del_init(tmp);
  		spin_lock(&dentry->d_lock);
  		if (atomic_read(&dentry->d_count)) {
  			spin_unlock(&dentry->d_lock);
  			continue;
  		}
  		prune_one_dentry(dentry);

  		cond_resched_lock(&dcache_lock);

  		goto repeat;
  	}
  	spin_unlock(&dcache_lock);
  }
  
  /*

   * destroy a single subtree of dentries for unmount
   * - see the comments on shrink_dcache_for_umount() for a description of the
   *   locking
   */
  static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
  {
  	struct dentry *parent;

  	unsigned detached = 0;

  
  	BUG_ON(!IS_ROOT(dentry));
  
  	/* detach this root from the system */
  	spin_lock(&dcache_lock);
  	if (!list_empty(&dentry->d_lru)) {
  		dentry_stat.nr_unused--;
  		list_del_init(&dentry->d_lru);
  	}
  	__d_drop(dentry);
  	spin_unlock(&dcache_lock);
  
  	for (;;) {
  		/* descend to the first leaf in the current subtree */
  		while (!list_empty(&dentry->d_subdirs)) {
  			struct dentry *loop;
  
  			/* this is a branch with children - detach all of them
  			 * from the system in one go */
  			spin_lock(&dcache_lock);
  			list_for_each_entry(loop, &dentry->d_subdirs,
  					    d_u.d_child) {
  				if (!list_empty(&loop->d_lru)) {
  					dentry_stat.nr_unused--;
  					list_del_init(&loop->d_lru);
  				}
  
  				__d_drop(loop);
  				cond_resched_lock(&dcache_lock);
  			}
  			spin_unlock(&dcache_lock);
  
  			/* move to the first child */
  			dentry = list_entry(dentry->d_subdirs.next,
  					    struct dentry, d_u.d_child);
  		}
  
  		/* consume the dentries from this leaf up through its parents
  		 * until we find one with children or run out altogether */
  		do {
  			struct inode *inode;
  
  			if (atomic_read(&dentry->d_count) != 0) {
  				printk(KERN_ERR
  				       "BUG: Dentry %p{i=%lx,n=%s}"
  				       " still in use (%d)"
  				       " [unmount of %s %s]
  ",
  				       dentry,
  				       dentry->d_inode ?
  				       dentry->d_inode->i_ino : 0UL,
  				       dentry->d_name.name,
  				       atomic_read(&dentry->d_count),
  				       dentry->d_sb->s_type->name,
  				       dentry->d_sb->s_id);
  				BUG();
  			}
  
  			parent = dentry->d_parent;
  			if (parent == dentry)
  				parent = NULL;
  			else
  				atomic_dec(&parent->d_count);
  
  			list_del(&dentry->d_u.d_child);

  			detached++;

  
  			inode = dentry->d_inode;
  			if (inode) {
  				dentry->d_inode = NULL;
  				list_del_init(&dentry->d_alias);
  				if (dentry->d_op && dentry->d_op->d_iput)
  					dentry->d_op->d_iput(dentry, inode);
  				else
  					iput(inode);
  			}
  
  			d_free(dentry);
  
  			/* finished when we fall off the top of the tree,
  			 * otherwise we ascend to the parent and move to the
  			 * next sibling if there is one */
  			if (!parent)

  				goto out;

  
  			dentry = parent;
  
  		} while (list_empty(&dentry->d_subdirs));
  
  		dentry = list_entry(dentry->d_subdirs.next,
  				    struct dentry, d_u.d_child);
  	}

  out:
  	/* several dentries were freed, need to correct nr_dentry */
  	spin_lock(&dcache_lock);
  	dentry_stat.nr_dentry -= detached;
  	spin_unlock(&dcache_lock);

  }
  
  /*
   * destroy the dentries attached to a superblock on unmounting
   * - we don't need to use dentry->d_lock, and only need dcache_lock when
   *   removing the dentry from the system lists and hashes because:
   *   - the superblock is detached from all mountings and open files, so the
   *     dentry trees will not be rearranged by the VFS
   *   - s_umount is write-locked, so the memory pressure shrinker will ignore
   *     any dentries belonging to this superblock that it comes across
   *   - the filesystem itself is no longer permitted to rearrange the dentries
   *     in this superblock
   */
  void shrink_dcache_for_umount(struct super_block *sb)
  {
  	struct dentry *dentry;
  
  	if (down_read_trylock(&sb->s_umount))
  		BUG();
  
  	dentry = sb->s_root;
  	sb->s_root = NULL;
  	atomic_dec(&dentry->d_count);
  	shrink_dcache_for_umount_subtree(dentry);
  
  	while (!hlist_empty(&sb->s_anon)) {
  		dentry = hlist_entry(sb->s_anon.first, struct dentry, d_hash);
  		shrink_dcache_for_umount_subtree(dentry);
  	}
  }
  
  /*

   * Search for at least 1 mount point in the dentry's subdirs.
   * We descend to the next level whenever the d_subdirs
   * list is non-empty and continue searching.
   */
   
  /**
   * have_submounts - check for mounts over a dentry
   * @parent: dentry to check.
   *
   * Return true if the parent or its subdirectories contain
   * a mount point
   */
   
  int have_submounts(struct dentry *parent)
  {
  	struct dentry *this_parent = parent;
  	struct list_head *next;
  
  	spin_lock(&dcache_lock);
  	if (d_mountpoint(parent))
  		goto positive;
  repeat:
  	next = this_parent->d_subdirs.next;
  resume:
  	while (next != &this_parent->d_subdirs) {
  		struct list_head *tmp = next;

  		struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);

  		next = tmp->next;
  		/* Have we found a mount point ? */
  		if (d_mountpoint(dentry))
  			goto positive;
  		if (!list_empty(&dentry->d_subdirs)) {
  			this_parent = dentry;
  			goto repeat;
  		}
  	}
  	/*
  	 * All done at this level ... ascend and resume the search.
  	 */
  	if (this_parent != parent) {

  		next = this_parent->d_u.d_child.next;

  		this_parent = this_parent->d_parent;
  		goto resume;
  	}
  	spin_unlock(&dcache_lock);
  	return 0; /* No mount points found in tree */
  positive:
  	spin_unlock(&dcache_lock);
  	return 1;
  }
  
  /*
   * Search the dentry child list for the specified parent,
   * and move any unused dentries to the end of the unused
   * list for prune_dcache(). We descend to the next level
   * whenever the d_subdirs list is non-empty and continue
   * searching.
   *
   * It returns zero iff there are no unused children,
   * otherwise  it returns the number of children moved to
   * the end of the unused list. This may not be the total
   * number of unused children, because select_parent can
   * drop the lock and return early due to latency
   * constraints.
   */
  static int select_parent(struct dentry * parent)
  {
  	struct dentry *this_parent = parent;
  	struct list_head *next;
  	int found = 0;
  
  	spin_lock(&dcache_lock);
  repeat:
  	next = this_parent->d_subdirs.next;
  resume:
  	while (next != &this_parent->d_subdirs) {
  		struct list_head *tmp = next;

  		struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);

  		next = tmp->next;
  
  		if (!list_empty(&dentry->d_lru)) {
  			dentry_stat.nr_unused--;
  			list_del_init(&dentry->d_lru);
  		}
  		/* 
  		 * move only zero ref count dentries to the end 
  		 * of the unused list for prune_dcache
  		 */
  		if (!atomic_read(&dentry->d_count)) {

  			list_add_tail(&dentry->d_lru, &dentry_unused);

  			dentry_stat.nr_unused++;
  			found++;
  		}
  
  		/*
  		 * We can return to the caller if we have found some (this
  		 * ensures forward progress). We'll be coming back to find
  		 * the rest.
  		 */
  		if (found && need_resched())
  			goto out;
  
  		/*
  		 * Descend a level if the d_subdirs list is non-empty.
  		 */
  		if (!list_empty(&dentry->d_subdirs)) {
  			this_parent = dentry;

  			goto repeat;
  		}
  	}
  	/*
  	 * All done at this level ... ascend and resume the search.
  	 */
  	if (this_parent != parent) {

  		next = this_parent->d_u.d_child.next;

  		this_parent = this_parent->d_parent;

  		goto resume;
  	}
  out:
  	spin_unlock(&dcache_lock);
  	return found;
  }
  
  /**
   * shrink_dcache_parent - prune dcache
   * @parent: parent of entries to prune
   *
   * Prune the dcache to remove unused children of the parent dentry.
   */
   
  void shrink_dcache_parent(struct dentry * parent)
  {
  	int found;
  
  	while ((found = select_parent(parent)) != 0)

  		prune_dcache(found, parent->d_sb);

  }

  /*
   * Scan `nr' dentries and return the number which remain.
   *
   * We need to avoid reentering the filesystem if the caller is performing a
   * GFP_NOFS allocation attempt.  One example deadlock is:
   *
   * ext2_new_block->getblk->GFP->shrink_dcache_memory->prune_dcache->
   * prune_one_dentry->dput->dentry_iput->iput->inode->i_sb->s_op->put_inode->
   * ext2_discard_prealloc->ext2_free_blocks->lock_super->DEADLOCK.
   *
   * In this case we return -1 to tell the caller that we baled.
   */

  static int shrink_dcache_memory(int nr, gfp_t gfp_mask)

  {
  	if (nr) {
  		if (!(gfp_mask & __GFP_FS))
  			return -1;

  		prune_dcache(nr, NULL);

  	}
  	return (dentry_stat.nr_unused / 100) * sysctl_vfs_cache_pressure;
  }
  
  /**
   * d_alloc	-	allocate a dcache entry
   * @parent: parent of entry to allocate
   * @name: qstr of the name
   *
   * Allocates a dentry. It returns %NULL if there is insufficient memory
   * available. On a success the dentry is returned. The name passed in is
   * copied and the copy passed in may be reused after this call.
   */
   
  struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
  {
  	struct dentry *dentry;
  	char *dname;
  
  	dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL); 
  	if (!dentry)
  		return NULL;
  
  	if (name->len > DNAME_INLINE_LEN-1) {
  		dname = kmalloc(name->len + 1, GFP_KERNEL);
  		if (!dname) {
  			kmem_cache_free(dentry_cache, dentry); 
  			return NULL;
  		}
  	} else  {
  		dname = dentry->d_iname;
  	}	
  	dentry->d_name.name = dname;
  
  	dentry->d_name.len = name->len;
  	dentry->d_name.hash = name->hash;
  	memcpy(dname, name->name, name->len);
  	dname[name->len] = 0;
  
  	atomic_set(&dentry->d_count, 1);
  	dentry->d_flags = DCACHE_UNHASHED;
  	spin_lock_init(&dentry->d_lock);
  	dentry->d_inode = NULL;
  	dentry->d_parent = NULL;
  	dentry->d_sb = NULL;
  	dentry->d_op = NULL;
  	dentry->d_fsdata = NULL;
  	dentry->d_mounted = 0;

  #ifdef CONFIG_PROFILING

  	dentry->d_cookie = NULL;

  #endif

  	INIT_HLIST_NODE(&dentry->d_hash);
  	INIT_LIST_HEAD(&dentry->d_lru);
  	INIT_LIST_HEAD(&dentry->d_subdirs);
  	INIT_LIST_HEAD(&dentry->d_alias);
  
  	if (parent) {
  		dentry->d_parent = dget(parent);
  		dentry->d_sb = parent->d_sb;
  	} else {

  		INIT_LIST_HEAD(&dentry->d_u.d_child);

  	}
  
  	spin_lock(&dcache_lock);
  	if (parent)

  		list_add(&dentry->d_u.d_child, &parent->d_subdirs);

  	dentry_stat.nr_dentry++;
  	spin_unlock(&dcache_lock);
  
  	return dentry;
  }
  
  struct dentry *d_alloc_name(struct dentry *parent, const char *name)
  {
  	struct qstr q;
  
  	q.name = name;
  	q.len = strlen(name);
  	q.hash = full_name_hash(q.name, q.len);
  	return d_alloc(parent, &q);
  }
  
  /**
   * d_instantiate - fill in inode information for a dentry
   * @entry: dentry to complete
   * @inode: inode to attach to this dentry
   *
   * Fill in inode information in the entry.
   *
   * This turns negative dentries into productive full members
   * of society.
   *
   * NOTE! This assumes that the inode count has been incremented
   * (or otherwise set) by the caller to indicate that it is now
   * in use by the dcache.
   */
   
  void d_instantiate(struct dentry *entry, struct inode * inode)
  {

  	BUG_ON(!list_empty(&entry->d_alias));

  	spin_lock(&dcache_lock);
  	if (inode)
  		list_add(&entry->d_alias, &inode->i_dentry);
  	entry->d_inode = inode;

  	fsnotify_d_instantiate(entry, inode);

  	spin_unlock(&dcache_lock);
  	security_d_instantiate(entry, inode);
  }
  
  /**
   * d_instantiate_unique - instantiate a non-aliased dentry
   * @entry: dentry to instantiate
   * @inode: inode to attach to this dentry
   *
   * Fill in inode information in the entry. On success, it returns NULL.
   * If an unhashed alias of "entry" already exists, then we return the

   * aliased dentry instead and drop one reference to inode.

   *
   * Note that in order to avoid conflicts with rename() etc, the caller
   * had better be holding the parent directory semaphore.

   *
   * This also assumes that the inode count has been incremented
   * (or otherwise set) by the caller to indicate that it is now
   * in use by the dcache.

   */

  static struct dentry *__d_instantiate_unique(struct dentry *entry,
  					     struct inode *inode)

  {
  	struct dentry *alias;
  	int len = entry->d_name.len;
  	const char *name = entry->d_name.name;
  	unsigned int hash = entry->d_name.hash;

  	if (!inode) {
  		entry->d_inode = NULL;
  		return NULL;
  	}

  	list_for_each_entry(alias, &inode->i_dentry, d_alias) {
  		struct qstr *qstr = &alias->d_name;
  
  		if (qstr->hash != hash)
  			continue;
  		if (alias->d_parent != entry->d_parent)
  			continue;
  		if (qstr->len != len)
  			continue;
  		if (memcmp(qstr->name, name, len))
  			continue;
  		dget_locked(alias);

  		return alias;
  	}

  	list_add(&entry->d_alias, &inode->i_dentry);

  	entry->d_inode = inode;

  	fsnotify_d_instantiate(entry, inode);

  	return NULL;
  }

  
  struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
  {
  	struct dentry *result;
  
  	BUG_ON(!list_empty(&entry->d_alias));
  
  	spin_lock(&dcache_lock);
  	result = __d_instantiate_unique(entry, inode);
  	spin_unlock(&dcache_lock);
  
  	if (!result) {
  		security_d_instantiate(entry, inode);
  		return NULL;
  	}
  
  	BUG_ON(!d_unhashed(result));
  	iput(inode);
  	return result;
  }

  EXPORT_SYMBOL(d_instantiate_unique);
  
  /**
   * d_alloc_root - allocate root dentry
   * @root_inode: inode to allocate the root for
   *
   * Allocate a root ("/") dentry for the inode given. The inode is
   * instantiated and returned. %NULL is returned if there is insufficient
   * memory or the inode passed is %NULL.
   */
   
  struct dentry * d_alloc_root(struct inode * root_inode)
  {
  	struct dentry *res = NULL;
  
  	if (root_inode) {
  		static const struct qstr name = { .name = "/", .len = 1 };
  
  		res = d_alloc(NULL, &name);
  		if (res) {
  			res->d_sb = root_inode->i_sb;
  			res->d_parent = res;
  			d_instantiate(res, root_inode);
  		}
  	}
  	return res;
  }
  
  static inline struct hlist_head *d_hash(struct dentry *parent,
  					unsigned long hash)
  {
  	hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES;
  	hash = hash ^ ((hash ^ GOLDEN_RATIO_PRIME) >> D_HASHBITS);
  	return dentry_hashtable + (hash & D_HASHMASK);
  }
  
  /**
   * d_alloc_anon - allocate an anonymous dentry
   * @inode: inode to allocate the dentry for
   *
   * This is similar to d_alloc_root.  It is used by filesystems when
   * creating a dentry for a given inode, often in the process of 
   * mapping a filehandle to a dentry.  The returned dentry may be
   * anonymous, or may have a full name (if the inode was already
   * in the cache).  The file system may need to make further
   * efforts to connect this dentry into the dcache properly.
   *
   * When called on a directory inode, we must ensure that
   * the inode only ever has one dentry.  If a dentry is
   * found, that is returned instead of allocating a new one.
   *
   * On successful return, the reference to the inode has been transferred
   * to the dentry.  If %NULL is returned (indicating kmalloc failure),
   * the reference on the inode has not been released.
   */
  
  struct dentry * d_alloc_anon(struct inode *inode)
  {
  	static const struct qstr anonstring = { .name = "" };
  	struct dentry *tmp;
  	struct dentry *res;
  
  	if ((res = d_find_alias(inode))) {
  		iput(inode);
  		return res;
  	}
  
  	tmp = d_alloc(NULL, &anonstring);
  	if (!tmp)
  		return NULL;
  
  	tmp->d_parent = tmp; /* make sure dput doesn't croak */
  	
  	spin_lock(&dcache_lock);
  	res = __d_find_alias(inode, 0);
  	if (!res) {
  		/* attach a disconnected dentry */
  		res = tmp;
  		tmp = NULL;
  		spin_lock(&res->d_lock);
  		res->d_sb = inode->i_sb;
  		res->d_parent = res;
  		res->d_inode = inode;
  		res->d_flags |= DCACHE_DISCONNECTED;
  		res->d_flags &= ~DCACHE_UNHASHED;
  		list_add(&res->d_alias, &inode->i_dentry);
  		hlist_add_head(&res->d_hash, &inode->i_sb->s_anon);
  		spin_unlock(&res->d_lock);
  
  		inode = NULL; /* don't drop reference */
  	}
  	spin_unlock(&dcache_lock);
  
  	if (inode)
  		iput(inode);
  	if (tmp)
  		dput(tmp);
  	return res;
  }
  
  
  /**
   * d_splice_alias - splice a disconnected dentry into the tree if one exists
   * @inode:  the inode which may have a disconnected dentry
   * @dentry: a negative dentry which we want to point to the inode.
   *
   * If inode is a directory and has a 'disconnected' dentry (i.e. IS_ROOT and
   * DCACHE_DISCONNECTED), then d_move that in place of the given dentry
   * and return it, else simply d_add the inode to the dentry and return NULL.
   *
   * This is needed in the lookup routine of any filesystem that is exportable
   * (via knfsd) so that we can build dcache paths to directories effectively.
   *
   * If a dentry was found and moved, then it is returned.  Otherwise NULL
   * is returned.  This matches the expected return value of ->lookup.
   *
   */
  struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
  {
  	struct dentry *new = NULL;

  	if (inode && S_ISDIR(inode->i_mode)) {

  		spin_lock(&dcache_lock);
  		new = __d_find_alias(inode, 1);
  		if (new) {
  			BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));

  			fsnotify_d_instantiate(new, inode);

  			spin_unlock(&dcache_lock);
  			security_d_instantiate(new, inode);
  			d_rehash(dentry);
  			d_move(new, dentry);
  			iput(inode);
  		} else {
  			/* d_instantiate takes dcache_lock, so we do it by hand */
  			list_add(&dentry->d_alias, &inode->i_dentry);
  			dentry->d_inode = inode;

  			fsnotify_d_instantiate(dentry, inode);

  			spin_unlock(&dcache_lock);
  			security_d_instantiate(dentry, inode);
  			d_rehash(dentry);
  		}
  	} else
  		d_add(dentry, inode);
  	return new;
  }
  
  
  /**
   * d_lookup - search for a dentry
   * @parent: parent dentry
   * @name: qstr of name we wish to find
   *
   * Searches the children of the parent dentry for the name in question. If
   * the dentry is found its reference count is incremented and the dentry
   * is returned. The caller must use d_put to free the entry when it has
   * finished using it. %NULL is returned on failure.
   *
   * __d_lookup is dcache_lock free. The hash list is protected using RCU.
   * Memory barriers are used while updating and doing lockless traversal. 
   * To avoid races with d_move while rename is happening, d_lock is used.
   *
   * Overflows in memcmp(), while d_move, are avoided by keeping the length
   * and name pointer in one structure pointed by d_qstr.
   *
   * rcu_read_lock() and rcu_read_unlock() are used to disable preemption while
   * lookup is going on.
   *
   * dentry_unused list is not updated even if lookup finds the required dentry
   * in there. It is updated in places such as prune_dcache, shrink_dcache_sb,
   * select_parent and __dget_locked. This laziness saves lookup from dcache_lock
   * acquisition.
   *
   * d_lookup() is protected against the concurrent renames in some unrelated
   * directory using the seqlockt_t rename_lock.
   */
  
  struct dentry * d_lookup(struct dentry * parent, struct qstr * name)
  {
  	struct dentry * dentry = NULL;
  	unsigned long seq;
  
          do {
                  seq = read_seqbegin(&rename_lock);
                  dentry = __d_lookup(parent, name);
                  if (dentry)
  			break;
  	} while (read_seqretry(&rename_lock, seq));
  	return dentry;
  }
  
  struct dentry * __d_lookup(struct dentry * parent, struct qstr * name)
  {
  	unsigned int len = name->len;
  	unsigned int hash = name->hash;
  	const unsigned char *str = name->name;
  	struct hlist_head *head = d_hash(parent,hash);
  	struct dentry *found = NULL;
  	struct hlist_node *node;

  	struct dentry *dentry;

  
  	rcu_read_lock();
  	

  	hlist_for_each_entry_rcu(dentry, node, head, d_hash) {

  		struct qstr *qstr;

  		if (dentry->d_name.hash != hash)
  			continue;
  		if (dentry->d_parent != parent)
  			continue;
  
  		spin_lock(&dentry->d_lock);
  
  		/*
  		 * Recheck the dentry after taking the lock - d_move may have
  		 * changed things.  Don't bother checking the hash because we're
  		 * about to compare the whole name anyway.
  		 */
  		if (dentry->d_parent != parent)
  			goto next;
  
  		/*
  		 * It is safe to compare names since d_move() cannot
  		 * change the qstr (protected by d_lock).
  		 */
  		qstr = &dentry->d_name;
  		if (parent->d_op && parent->d_op->d_compare) {
  			if (parent->d_op->d_compare(parent, qstr, name))
  				goto next;
  		} else {
  			if (qstr->len != len)
  				goto next;
  			if (memcmp(qstr->name, str, len))
  				goto next;
  		}
  
  		if (!d_unhashed(dentry)) {
  			atomic_inc(&dentry->d_count);
  			found = dentry;
  		}
  		spin_unlock(&dentry->d_lock);
  		break;
  next:
  		spin_unlock(&dentry->d_lock);
   	}
   	rcu_read_unlock();
  
   	return found;
  }
  
  /**

   * d_hash_and_lookup - hash the qstr then search for a dentry
   * @dir: Directory to search in
   * @name: qstr of name we wish to find
   *
   * On hash failure or on lookup failure NULL is returned.
   */
  struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
  {
  	struct dentry *dentry = NULL;
  
  	/*
  	 * Check for a fs-specific hash function. Note that we must
  	 * calculate the standard hash first, as the d_op->d_hash()
  	 * routine may choose to leave the hash value unchanged.
  	 */
  	name->hash = full_name_hash(name->name, name->len);
  	if (dir->d_op && dir->d_op->d_hash) {
  		if (dir->d_op->d_hash(dir, name) < 0)
  			goto out;
  	}
  	dentry = d_lookup(dir, name);
  out:
  	return dentry;
  }
  
  /**

   * d_validate - verify dentry provided from insecure source
   * @dentry: The dentry alleged to be valid child of @dparent
   * @dparent: The parent dentry (known to be valid)
   * @hash: Hash of the dentry
   * @len: Length of the name
   *
   * An insecure source has sent us a dentry, here we verify it and dget() it.
   * This is used by ncpfs in its readdir implementation.
   * Zero is returned in the dentry is invalid.
   */
   
  int d_validate(struct dentry *dentry, struct dentry *dparent)
  {
  	struct hlist_head *base;
  	struct hlist_node *lhp;
  
  	/* Check whether the ptr might be valid at all.. */
  	if (!kmem_ptr_validate(dentry_cache, dentry))
  		goto out;
  
  	if (dentry->d_parent != dparent)
  		goto out;
  
  	spin_lock(&dcache_lock);
  	base = d_hash(dparent, dentry->d_name.hash);
  	hlist_for_each(lhp,base) { 

  		/* hlist_for_each_entry_rcu() not required for d_hash list

  		 * as it is parsed under dcache_lock
  		 */
  		if (dentry == hlist_entry(lhp, struct dentry, d_hash)) {
  			__dget_locked(dentry);
  			spin_unlock(&dcache_lock);
  			return 1;
  		}
  	}
  	spin_unlock(&dcache_lock);
  out:
  	return 0;
  }
  
  /*
   * When a file is deleted, we have two options:
   * - turn this dentry into a negative dentry
   * - unhash this dentry and free it.
   *
   * Usually, we want to just turn this into
   * a negative dentry, but if anybody else is
   * currently using the dentry or the inode
   * we can't do that and we fall back on removing
   * it from the hash queues and waiting for
   * it to be deleted later when it has no users
   */
   
  /**
   * d_delete - delete a dentry
   * @dentry: The dentry to delete
   *
   * Turn the dentry into a negative dentry if possible, otherwise
   * remove it from the hash queues so it can be deleted later
   */
   
  void d_delete(struct dentry * dentry)
  {

  	int isdir = 0;

  	/*
  	 * Are we the only user?
  	 */
  	spin_lock(&dcache_lock);
  	spin_lock(&dentry->d_lock);

  	isdir = S_ISDIR(dentry->d_inode->i_mode);

  	if (atomic_read(&dentry->d_count) == 1) {
  		dentry_iput(dentry);

  		fsnotify_nameremove(dentry, isdir);

  
  		/* remove this and other inotify debug checks after 2.6.18 */
  		dentry->d_flags &= ~DCACHE_INOTIFY_PARENT_WATCHED;

  		return;
  	}
  
  	if (!d_unhashed(dentry))
  		__d_drop(dentry);
  
  	spin_unlock(&dentry->d_lock);
  	spin_unlock(&dcache_lock);

  
  	fsnotify_nameremove(dentry, isdir);

  }
  
  static void __d_rehash(struct dentry * entry, struct hlist_head *list)
  {
  
   	entry->d_flags &= ~DCACHE_UNHASHED;
   	hlist_add_head_rcu(&entry->d_hash, list);
  }

  static void _d_rehash(struct dentry * entry)
  {
  	__d_rehash(entry, d_hash(entry->d_parent, entry->d_name.hash));
  }

  /**
   * d_rehash	- add an entry back to the hash
   * @entry: dentry to add to the hash
   *
   * Adds a dentry to the hash according to its name.
   */
   
  void d_rehash(struct dentry * entry)
  {

  	spin_lock(&dcache_lock);
  	spin_lock(&entry->d_lock);

  	_d_rehash(entry);

  	spin_unlock(&entry->d_lock);
  	spin_unlock(&dcache_lock);
  }
  
  #define do_switch(x,y) do { \
  	__typeof__ (x) __tmp = x; \
  	x = y; y = __tmp; } while (0)
  
  /*
   * When switching names, the actual string doesn't strictly have to
   * be preserved in the target - because we're dropping the target
   * anyway. As such, we can just do a simple memcpy() to copy over
   * the new name before we switch.
   *
   * Note that we have to be a lot more careful about getting the hash
   * switched - we have to switch the hash value properly even if it
   * then no longer matches the actual (corrupted) string of the target.
   * The hash value has to match the hash queue that the dentry is on..
   */
  static void switch_names(struct dentry *dentry, struct dentry *target)
  {
  	if (dname_external(target)) {
  		if (dname_external(dentry)) {
  			/*
  			 * Both external: swap the pointers
  			 */
  			do_switch(target->d_name.name, dentry->d_name.name);
  		} else {
  			/*
  			 * dentry:internal, target:external.  Steal target's
  			 * storage and make target internal.
  			 */
  			dentry->d_name.name = target->d_name.name;
  			target->d_name.name = target->d_iname;
  		}
  	} else {
  		if (dname_external(dentry)) {
  			/*
  			 * dentry:external, target:internal.  Give dentry's
  			 * storage to target and make dentry internal
  			 */
  			memcpy(dentry->d_iname, target->d_name.name,
  					target->d_name.len + 1);
  			target->d_name.name = dentry->d_name.name;
  			dentry->d_name.name = dentry->d_iname;
  		} else {
  			/*
  			 * Both are internal.  Just copy target to dentry
  			 */
  			memcpy(dentry->d_iname, target->d_name.name,
  					target->d_name.len + 1);
  		}
  	}
  }
  
  /*
   * We cannibalize "target" when moving dentry on top of it,
   * because it's going to be thrown away anyway. We could be more
   * polite about it, though.
   *
   * This forceful removal will result in ugly /proc output if
   * somebody holds a file open that got deleted due to a rename.
   * We could be nicer about the deleted file, and let it show
   * up under the name it got deleted rather than the name that
   * deleted it.
   */
   

  /*
   * d_move_locked - move a dentry

   * @dentry: entry to move
   * @target: new dentry
   *
   * Update the dcache to reflect the move of a file name. Negative
   * dcache entries should not be moved in this way.
   */

  static void d_move_locked(struct dentry * dentry, struct dentry * target)

  {
  	struct hlist_head *list;
  
  	if (!dentry->d_inode)
  		printk(KERN_WARNING "VFS: moving negative dcache entry
  ");

  	write_seqlock(&rename_lock);
  	/*
  	 * XXXX: do we really need to take target->d_lock?
  	 */
  	if (target < dentry) {
  		spin_lock(&target->d_lock);

  		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);

  	} else {
  		spin_lock(&dentry->d_lock);

  		spin_lock_nested(&target->d_lock, DENTRY_D_LOCK_NESTED);

  	}
  
  	/* Move the dentry to the target hash queue, if on different bucket */
  	if (dentry->d_flags & DCACHE_UNHASHED)
  		goto already_unhashed;
  
  	hlist_del_rcu(&dentry->d_hash);
  
  already_unhashed:
  	list = d_hash(target->d_parent, target->d_name.hash);
  	__d_rehash(dentry, list);
  
  	/* Unhash the target: dput() will then get rid of it */
  	__d_drop(target);

  	list_del(&dentry->d_u.d_child);
  	list_del(&target->d_u.d_child);

  
  	/* Switch the names.. */
  	switch_names(dentry, target);
  	do_switch(dentry->d_name.len, target->d_name.len);
  	do_switch(dentry->d_name.hash, target->d_name.hash);
  
  	/* ... and switch the parents */
  	if (IS_ROOT(dentry)) {
  		dentry->d_parent = target->d_parent;
  		target->d_parent = target;

  		INIT_LIST_HEAD(&target->d_u.d_child);

  	} else {
  		do_switch(dentry->d_parent, target->d_parent);
  
  		/* And add them back to the (new) parent lists */

  		list_add(&target->d_u.d_child, &target->d_parent->d_subdirs);

  	}

  	list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);

  	spin_unlock(&target->d_lock);

  	fsnotify_d_move(dentry);

  	spin_unlock(&dentry->d_lock);
  	write_sequnlock(&rename_lock);

  }
  
  /**
   * d_move - move a dentry
   * @dentry: entry to move
   * @target: new dentry
   *
   * Update the dcache to reflect the move of a file name. Negative
   * dcache entries should not be moved in this way.
   */
  
  void d_move(struct dentry * dentry, struct dentry * target)
  {
  	spin_lock(&dcache_lock);
  	d_move_locked(dentry, target);

  	spin_unlock(&dcache_lock);
  }

  /*

   * Helper that returns 1 if p1 is a parent of p2, else 0
   */
  static int d_isparent(struct dentry *p1, struct dentry *p2)
  {
  	struct dentry *p;
  
  	for (p = p2; p->d_parent != p; p = p->d_parent) {
  		if (p->d_parent == p1)
  			return 1;
  	}
  	return 0;
  }
  
  /*
   * This helper attempts to cope with remotely renamed directories
   *
   * It assumes that the caller is already holding
   * dentry->d_parent->d_inode->i_mutex and the dcache_lock
   *
   * Note: If ever the locking in lock_rename() changes, then please
   * remember to update this too...
   *
   * On return, dcache_lock will have been unlocked.
   */
  static struct dentry *__d_unalias(struct dentry *dentry, struct dentry *alias)
  {
  	struct mutex *m1 = NULL, *m2 = NULL;
  	struct dentry *ret;
  
  	/* If alias and dentry share a parent, then no extra locks required */
  	if (alias->d_parent == dentry->d_parent)
  		goto out_unalias;
  
  	/* Check for loops */
  	ret = ERR_PTR(-ELOOP);
  	if (d_isparent(alias, dentry))
  		goto out_err;
  
  	/* See lock_rename() */
  	ret = ERR_PTR(-EBUSY);
  	if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
  		goto out_err;
  	m1 = &dentry->d_sb->s_vfs_rename_mutex;
  	if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex))
  		goto out_err;
  	m2 = &alias->d_parent->d_inode->i_mutex;
  out_unalias:
  	d_move_locked(alias, dentry);
  	ret = alias;
  out_err:
  	spin_unlock(&dcache_lock);
  	if (m2)
  		mutex_unlock(m2);
  	if (m1)
  		mutex_unlock(m1);
  	return ret;
  }
  
  /*

   * Prepare an anonymous dentry for life in the superblock's dentry tree as a
   * named dentry in place of the dentry to be replaced.
   */
  static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
  {
  	struct dentry *dparent, *aparent;
  
  	switch_names(dentry, anon);
  	do_switch(dentry->d_name.len, anon->d_name.len);
  	do_switch(dentry->d_name.hash, anon->d_name.hash);
  
  	dparent = dentry->d_parent;
  	aparent = anon->d_parent;
  
  	dentry->d_parent = (aparent == anon) ? dentry : aparent;
  	list_del(&dentry->d_u.d_child);
  	if (!IS_ROOT(dentry))
  		list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
  	else
  		INIT_LIST_HEAD(&dentry->d_u.d_child);
  
  	anon->d_parent = (dparent == dentry) ? anon : dparent;
  	list_del(&anon->d_u.d_child);
  	if (!IS_ROOT(anon))
  		list_add(&anon->d_u.d_child, &anon->d_parent->d_subdirs);
  	else
  		INIT_LIST_HEAD(&anon->d_u.d_child);
  
  	anon->d_flags &= ~DCACHE_DISCONNECTED;
  }
  
  /**
   * d_materialise_unique - introduce an inode into the tree
   * @dentry: candidate dentry
   * @inode: inode to bind to the dentry, to which aliases may be attached
   *
   * Introduces an dentry into the tree, substituting an extant disconnected
   * root directory alias in its place if there is one
   */
  struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
  {

  	struct dentry *actual;

  
  	BUG_ON(!d_unhashed(dentry));
  
  	spin_lock(&dcache_lock);
  
  	if (!inode) {
  		actual = dentry;
  		dentry->d_inode = NULL;
  		goto found_lock;
  	}

  	if (S_ISDIR(inode->i_mode)) {
  		struct dentry *alias;
  
  		/* Does an aliased dentry already exist? */
  		alias = __d_find_alias(inode, 0);
  		if (alias) {
  			actual = alias;
  			/* Is this an anonymous mountpoint that we could splice
  			 * into our tree? */
  			if (IS_ROOT(alias)) {
  				spin_lock(&alias->d_lock);
  				__d_materialise_dentry(dentry, alias);
  				__d_drop(alias);
  				goto found;
  			}
  			/* Nope, but we must(!) avoid directory aliasing */
  			actual = __d_unalias(dentry, alias);
  			if (IS_ERR(actual))
  				dput(alias);
  			goto out_nolock;
  		}

  	}
  
  	/* Add a unique reference */
  	actual = __d_instantiate_unique(dentry, inode);
  	if (!actual)
  		actual = dentry;
  	else if (unlikely(!d_unhashed(actual)))
  		goto shouldnt_be_hashed;
  
  found_lock:
  	spin_lock(&actual->d_lock);
  found:
  	_d_rehash(actual);
  	spin_unlock(&actual->d_lock);
  	spin_unlock(&dcache_lock);

  out_nolock:

  	if (actual == dentry) {
  		security_d_instantiate(dentry, inode);
  		return NULL;
  	}
  
  	iput(inode);
  	return actual;

  shouldnt_be_hashed:
  	spin_unlock(&dcache_lock);
  	BUG();
  	goto shouldnt_be_hashed;
  }

  /**
   * d_path - return the path of a dentry
   * @dentry: dentry to report
   * @vfsmnt: vfsmnt to which the dentry belongs
   * @root: root dentry
   * @rootmnt: vfsmnt to which the root dentry belongs
   * @buffer: buffer to return value in
   * @buflen: buffer length
   *

   * Convert a dentry into an ASCII path name. If the entry has been deleted
   * the string " (deleted)" is appended. Note that this is ambiguous.

   *

   * Returns the buffer or an error code if the path was too long.
   *
   * "buflen" should be positive. Caller holds the dcache_lock.

   */

  static char * __d_path( struct dentry *dentry, struct vfsmount *vfsmnt,
  			struct dentry *root, struct vfsmount *rootmnt,
  			char *buffer, int buflen)

  {

  	char * end = buffer+buflen;
  	char * retval;
  	int namelen;

  	*--end = '\0';
  	buflen--;

  	if (!IS_ROOT(dentry) && d_unhashed(dentry)) {

  		buflen -= 10;

  		end -= 10;
  		if (buflen < 0)
  			goto Elong;
  		memcpy(end, " (deleted)", 10);

  	}

  
  	if (buflen < 1)
  		goto Elong;
  	/* Get '/' right */
  	retval = end-1;
  	*retval = '/';
  
  	for (;;) {

  		struct dentry * parent;

  		if (dentry == root && vfsmnt == rootmnt)
  			break;

  		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {

  			/* Global root? */

  			spin_lock(&vfsmount_lock);
  			if (vfsmnt->mnt_parent == vfsmnt) {
  				spin_unlock(&vfsmount_lock);
  				goto global_root;
  			}
  			dentry = vfsmnt->mnt_mountpoint;
  			vfsmnt = vfsmnt->mnt_parent;
  			spin_unlock(&vfsmount_lock);
  			continue;
  		}
  		parent = dentry->d_parent;
  		prefetch(parent);
  		namelen = dentry->d_name.len;

  		buflen -= namelen + 1;

  		if (buflen < 0)
  			goto Elong;
  		end -= namelen;
  		memcpy(end, dentry->d_name.name, namelen);
  		*--end = '/';
  		retval = end;

  		dentry = parent;
  	}

  	return retval;

  
  global_root:
  	namelen = dentry->d_name.len;

  	buflen -= namelen;
  	if (buflen < 0)

  		goto Elong;

  	retval -= namelen-1;	/* hit the slash */
  	memcpy(retval, dentry->d_name.name, namelen);
  	return retval;

  Elong:

  	return ERR_PTR(-ENAMETOOLONG);

  }
  
  /* write full pathname into buffer and return start of pathname */

  char * d_path(struct dentry *dentry, struct vfsmount *vfsmnt,
  				char *buf, int buflen)

  {
  	char *res;
  	struct vfsmount *rootmnt;
  	struct dentry *root;
  
  	read_lock(&current->fs->lock);
  	rootmnt = mntget(current->fs->rootmnt);
  	root = dget(current->fs->root);
  	read_unlock(&current->fs->lock);

  	spin_lock(&dcache_lock);
  	res = __d_path(dentry, vfsmnt, root, rootmnt, buf, buflen);
  	spin_unlock(&dcache_lock);

  	dput(root);
  	mntput(rootmnt);
  	return res;
  }
  
  /*
   * NOTE! The user-level library version returns a
   * character pointer. The kernel system call just
   * returns the length of the buffer filled (which
   * includes the ending '\0' character), or a negative
   * error value. So libc would do something like
   *
   *	char *getcwd(char * buf, size_t size)
   *	{
   *		int retval;
   *
   *		retval = sys_getcwd(buf, size);
   *		if (retval >= 0)
   *			return buf;
   *		errno = -retval;
   *		return NULL;
   *	}
   */
  asmlinkage long sys_getcwd(char __user *buf, unsigned long size)
  {

  	int error;

  	struct vfsmount *pwdmnt, *rootmnt;
  	struct dentry *pwd, *root;

  	char *page = (char *) __get_free_page(GFP_USER);

  
  	if (!page)
  		return -ENOMEM;
  
  	read_lock(&current->fs->lock);
  	pwdmnt = mntget(current->fs->pwdmnt);
  	pwd = dget(current->fs->pwd);
  	rootmnt = mntget(current->fs->rootmnt);
  	root = dget(current->fs->root);
  	read_unlock(&current->fs->lock);

  	error = -ENOENT;
  	/* Has the current directory has been unlinked? */
  	spin_lock(&dcache_lock);
  	if (pwd->d_parent == pwd || !d_unhashed(pwd)) {
  		unsigned long len;
  		char * cwd;

  		cwd = __d_path(pwd, pwdmnt, root, rootmnt, page, PAGE_SIZE);
  		spin_unlock(&dcache_lock);
  
  		error = PTR_ERR(cwd);
  		if (IS_ERR(cwd))
  			goto out;
  
  		error = -ERANGE;
  		len = PAGE_SIZE + page - cwd;
  		if (len <= size) {
  			error = len;
  			if (copy_to_user(buf, cwd, len))
  				error = -EFAULT;
  		}
  	} else
  		spin_unlock(&dcache_lock);

  
  out:
  	dput(pwd);
  	mntput(pwdmnt);
  	dput(root);
  	mntput(rootmnt);
  	free_page((unsigned long) page);
  	return error;
  }
  
  /*
   * Test whether new_dentry is a subdirectory of old_dentry.
   *
   * Trivially implemented using the dcache structure
   */
  
  /**
   * is_subdir - is new dentry a subdirectory of old_dentry
   * @new_dentry: new dentry
   * @old_dentry: old dentry
   *
   * Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
   * Returns 0 otherwise.
   * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
   */
    
  int is_subdir(struct dentry * new_dentry, struct dentry * old_dentry)
  {
  	int result;
  	struct dentry * saved = new_dentry;
  	unsigned long seq;
  
  	/* need rcu_readlock to protect against the d_parent trashing due to
  	 * d_move
  	 */
  	rcu_read_lock();
          do {
  		/* for restarting inner loop in case of seq retry */
  		new_dentry = saved;
  		result = 0;
  		seq = read_seqbegin(&rename_lock);
  		for (;;) {
  			if (new_dentry != old_dentry) {
  				struct dentry * parent = new_dentry->d_parent;
  				if (parent == new_dentry)
  					break;
  				new_dentry = parent;
  				continue;
  			}
  			result = 1;
  			break;
  		}
  	} while (read_seqretry(&rename_lock, seq));
  	rcu_read_unlock();
  
  	return result;
  }
  
  void d_genocide(struct dentry *root)
  {
  	struct dentry *this_parent = root;
  	struct list_head *next;
  
  	spin_lock(&dcache_lock);
  repeat:
  	next = this_parent->d_subdirs.next;
  resume:
  	while (next != &this_parent->d_subdirs) {
  		struct list_head *tmp = next;

  		struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);

  		next = tmp->next;
  		if (d_unhashed(dentry)||!dentry->d_inode)
  			continue;
  		if (!list_empty(&dentry->d_subdirs)) {
  			this_parent = dentry;
  			goto repeat;
  		}
  		atomic_dec(&dentry->d_count);
  	}
  	if (this_parent != root) {

  		next = this_parent->d_u.d_child.next;

  		atomic_dec(&this_parent->d_count);
  		this_parent = this_parent->d_parent;
  		goto resume;
  	}
  	spin_unlock(&dcache_lock);
  }
  
  /**
   * find_inode_number - check for dentry with name
   * @dir: directory to check
   * @name: Name to find.
   *
   * Check whether a dentry already exists for the given name,
   * and return the inode number if it has an inode. Otherwise
   * 0 is returned.
   *
   * This routine is used to post-process directory listings for
   * filesystems using synthetic inode numbers, and is necessary
   * to keep getcwd() working.
   */
   
  ino_t find_inode_number(struct dentry *dir, struct qstr *name)
  {
  	struct dentry * dentry;
  	ino_t ino = 0;

  	dentry = d_hash_and_lookup(dir, name);
  	if (dentry) {

  		if (dentry->d_inode)
  			ino = dentry->d_inode->i_ino;
  		dput(dentry);
  	}

  	return ino;
  }
  
  static __initdata unsigned long dhash_entries;
  static int __init set_dhash_entries(char *str)
  {
  	if (!str)
  		return 0;
  	dhash_entries = simple_strtoul(str, &str, 0);
  	return 1;
  }
  __setup("dhash_entries=", set_dhash_entries);
  
  static void __init dcache_init_early(void)
  {
  	int loop;
  
  	/* If hashes are distributed across NUMA nodes, defer
  	 * hash allocation until vmalloc space is available.
  	 */
  	if (hashdist)
  		return;
  
  	dentry_hashtable =
  		alloc_large_system_hash("Dentry cache",
  					sizeof(struct hlist_head),
  					dhash_entries,
  					13,
  					HASH_EARLY,
  					&d_hash_shift,
  					&d_hash_mask,
  					0);
  
  	for (loop = 0; loop < (1 << d_hash_shift); loop++)
  		INIT_HLIST_HEAD(&dentry_hashtable[loop]);
  }
  
  static void __init dcache_init(unsigned long mempages)
  {
  	int loop;
  
  	/* 
  	 * A constructor could be added for stable state like the lists,
  	 * but it is probably not worth it because of the cache nature
  	 * of the dcache. 
  	 */
  	dentry_cache = kmem_cache_create("dentry_cache",
  					 sizeof(struct dentry),
  					 0,

  					 (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
  					 SLAB_MEM_SPREAD),

  					 NULL, NULL);
  	
  	set_shrinker(DEFAULT_SEEKS, shrink_dcache_memory);
  
  	/* Hash may have been set up in dcache_init_early */
  	if (!hashdist)
  		return;
  
  	dentry_hashtable =
  		alloc_large_system_hash("Dentry cache",
  					sizeof(struct hlist_head),
  					dhash_entries,
  					13,
  					0,
  					&d_hash_shift,
  					&d_hash_mask,
  					0);
  
  	for (loop = 0; loop < (1 << d_hash_shift); loop++)
  		INIT_HLIST_HEAD(&dentry_hashtable[loop]);
  }
  
  /* SLAB cache for __getname() consumers */

  struct kmem_cache *names_cachep __read_mostly;

  
  /* SLAB cache for file structures */

  struct kmem_cache *filp_cachep __read_mostly;

  
  EXPORT_SYMBOL(d_genocide);

  void __init vfs_caches_init_early(void)
  {
  	dcache_init_early();
  	inode_init_early();
  }
  
  void __init vfs_caches_init(unsigned long mempages)
  {
  	unsigned long reserve;
  
  	/* Base hash sizes on available memory, with a reserve equal to
             150% of current kernel size */
  
  	reserve = min((mempages - nr_free_pages()) * 3/2, mempages - 1);
  	mempages -= reserve;
  
  	names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
  			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
  
  	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,

  			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);

  
  	dcache_init(mempages);
  	inode_init(mempages);
  	files_init(mempages);
  	mnt_init(mempages);
  	bdev_cache_init();
  	chrdev_init();
  }
  
  EXPORT_SYMBOL(d_alloc);
  EXPORT_SYMBOL(d_alloc_anon);
  EXPORT_SYMBOL(d_alloc_root);
  EXPORT_SYMBOL(d_delete);
  EXPORT_SYMBOL(d_find_alias);
  EXPORT_SYMBOL(d_instantiate);
  EXPORT_SYMBOL(d_invalidate);
  EXPORT_SYMBOL(d_lookup);
  EXPORT_SYMBOL(d_move);

  EXPORT_SYMBOL_GPL(d_materialise_unique);

  EXPORT_SYMBOL(d_path);
  EXPORT_SYMBOL(d_prune_aliases);
  EXPORT_SYMBOL(d_rehash);
  EXPORT_SYMBOL(d_splice_alias);
  EXPORT_SYMBOL(d_validate);
  EXPORT_SYMBOL(dget_locked);
  EXPORT_SYMBOL(dput);
  EXPORT_SYMBOL(find_inode_number);
  EXPORT_SYMBOL(have_submounts);
  EXPORT_SYMBOL(names_cachep);
  EXPORT_SYMBOL(shrink_dcache_parent);
  EXPORT_SYMBOL(shrink_dcache_sb);