/*
 * 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/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 <linux/fs_struct.h>
#include <linux/hardirq.h>
#include <linux/bit_spinlock.h>
#include <linux/rculist_bl.h>
#include <linux/prefetch.h>
#include <linux/ratelimit.h>
#include "internal.h"

/*
 * Usage:
 * dcache->d_inode->i_lock protects:
 *   - i_dentry, d_alias, d_inode of aliases
 * dcache_hash_bucket lock protects:
 *   - the dcache hash table
 * s_anon bl list spinlock protects:
 *   - the s_anon list (see __d_drop)
 * dcache_lru_lock protects:
 *   - the dcache lru lists and counters
 * d_lock protects:
 *   - d_flags
 *   - d_name
 *   - d_lru
 *   - d_count
 *   - d_unhashed()
 *   - d_parent and d_subdirs
 *   - childrens' d_child and d_parent
 *   - d_alias, d_inode
 *
 * Ordering:
 * dentry->d_inode->i_lock
 *   dentry->d_lock
 *     dcache_lru_lock
 *     dcache_hash_bucket lock
 *     s_anon lock
 *
 * If there is an ancestor relationship:
 * dentry->d_parent->...->d_parent->d_lock
 *   ...
 *     dentry->d_parent->d_lock
 *       dentry->d_lock
 *
 * If no ancestor relationship:
 * if (dentry1 < dentry2)
 *   dentry1->d_lock
 *     dentry2->d_lock
 */
int sysctl_vfs_cache_pressure __read_mostly = 100;
EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);

static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lru_lock);
__cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);

EXPORT_SYMBOL(rename_lock);

static struct kmem_cache *dentry_cache __read_mostly;

/*
 * 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_bl_head *dentry_hashtable __read_mostly;

static inline struct hlist_bl_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);
}

/* Statistics gathering. */
struct dentry_stat_t dentry_stat = {
        .age_limit = 45,
};

static DEFINE_PER_CPU(unsigned int, nr_dentry);

#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
static int get_nr_dentry(void)
{
        int i;
        int sum = 0;
        for_each_possible_cpu(i)
                sum += per_cpu(nr_dentry, i);
        return sum < 0 ? 0 : sum;
}

int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,
                   size_t *lenp, loff_t *ppos)
{
        dentry_stat.nr_dentry = get_nr_dentry();
        return proc_dointvec(table, write, buffer, lenp, ppos);
}
#endif

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

        WARN_ON(!list_empty(&dentry->d_alias));
        if (dname_external(dentry))
                kfree(dentry->d_name.name);
        kmem_cache_free(dentry_cache, dentry); 
}

/*
 * no locks, please.
 */
static void d_free(struct dentry *dentry)
{
        BUG_ON(dentry->d_count);
        this_cpu_dec(nr_dentry);
        if (dentry->d_op && dentry->d_op->d_release)
                dentry->d_op->d_release(dentry);

        /* if dentry was never visible to RCU, immediate free is OK */
        if (!(dentry->d_flags & DCACHE_RCUACCESS))
                __d_free(&dentry->d_u.d_rcu);
        else
                call_rcu(&dentry->d_u.d_rcu, __d_free);
}

/**
 * dentry_rcuwalk_barrier - invalidate in-progress rcu-walk lookups
 * @dentry: the target dentry
 * After this call, in-progress rcu-walk path lookup will fail. This
 * should be called after unhashing, and after changing d_inode (if
 * the dentry has not already been unhashed).
 */
static inline void dentry_rcuwalk_barrier(struct dentry *dentry)
{
        assert_spin_locked(&dentry->d_lock);
        /* Go through a barrier */
        write_seqcount_barrier(&dentry->d_seq);
}

/*
 * Release the dentry's inode, using the filesystem
 * d_iput() operation if defined. Dentry has no refcount
 * and is unhashed.
 */
static void dentry_iput(struct dentry * dentry)
        __releases(dentry->d_lock)
        __releases(dentry->d_inode->i_lock)
{
        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(&inode->i_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);
        }
}

/*
 * Release the dentry's inode, using the filesystem
 * d_iput() operation if defined. dentry remains in-use.
 */
static void dentry_unlink_inode(struct dentry * dentry)
        __releases(dentry->d_lock)
        __releases(dentry->d_inode->i_lock)
{
        struct inode *inode = dentry->d_inode;
        dentry->d_inode = NULL;
        list_del_init(&dentry->d_alias);
        dentry_rcuwalk_barrier(dentry);
        spin_unlock(&dentry->d_lock);
        spin_unlock(&inode->i_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);
}

/*
 * dentry_lru_(add|del|prune|move_tail) must be called with d_lock held.
 */
static void dentry_lru_add(struct dentry *dentry)
{
        if (list_empty(&dentry->d_lru)) {
                spin_lock(&dcache_lru_lock);
                list_add(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
                dentry->d_sb->s_nr_dentry_unused++;
                dentry_stat.nr_unused++;
                spin_unlock(&dcache_lru_lock);
        }
}

static void __dentry_lru_del(struct dentry *dentry)
{
        list_del_init(&dentry->d_lru);
        dentry->d_sb->s_nr_dentry_unused--;
        dentry_stat.nr_unused--;
}

/*
 * Remove a dentry with references from the LRU.
 */
static void dentry_lru_del(struct dentry *dentry)
{
        if (!list_empty(&dentry->d_lru)) {
                spin_lock(&dcache_lru_lock);
                __dentry_lru_del(dentry);
                spin_unlock(&dcache_lru_lock);
        }
}

/*
 * Remove a dentry that is unreferenced and about to be pruned
 * (unhashed and destroyed) from the LRU, and inform the file system.
 * This wrapper should be called _prior_ to unhashing a victim dentry.
 */
static void dentry_lru_prune(struct dentry *dentry)
{
        if (!list_empty(&dentry->d_lru)) {
                if (dentry->d_flags & DCACHE_OP_PRUNE)
                        dentry->d_op->d_prune(dentry);

                spin_lock(&dcache_lru_lock);
                __dentry_lru_del(dentry);
                spin_unlock(&dcache_lru_lock);
        }
}

static void dentry_lru_move_tail(struct dentry *dentry)
{
        spin_lock(&dcache_lru_lock);
        if (list_empty(&dentry->d_lru)) {
                list_add_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
                dentry->d_sb->s_nr_dentry_unused++;
                dentry_stat.nr_unused++;
        } else {
                list_move_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
        }
        spin_unlock(&dcache_lru_lock);
}

/**
 * d_kill - kill dentry and return parent
 * @dentry: dentry to kill
 * @parent: parent dentry
 *
 * The dentry must already be unhashed and removed from the LRU.
 *
 * If this is the root of the dentry tree, return NULL.
 *
 * dentry->d_lock and parent->d_lock must be held by caller, and are dropped by
 * d_kill.
 */
static struct dentry *d_kill(struct dentry *dentry, struct dentry *parent)
        __releases(dentry->d_lock)
        __releases(parent->d_lock)
        __releases(dentry->d_inode->i_lock)
{
        list_del(&dentry->d_u.d_child);
        /*
         * Inform try_to_ascend() that we are no longer attached to the
         * dentry tree
         */
        dentry->d_flags |= DCACHE_DISCONNECTED;
        if (parent)
                spin_unlock(&parent->d_lock);
        dentry_iput(dentry);
        /*
         * dentry_iput drops the locks, at which point nobody (except
         * transient RCU lookups) can reach this dentry.
         */
        d_free(dentry);
        return parent;
}

/*
 * Unhash a dentry without inserting an RCU walk barrier or checking that
 * dentry->d_lock is locked.  The caller must take care of that, if
 * appropriate.
 */
static void __d_shrink(struct dentry *dentry)
{
        if (!d_unhashed(dentry)) {
                struct hlist_bl_head *b;
                if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
                        b = &dentry->d_sb->s_anon;
                else
                        b = d_hash(dentry->d_parent, dentry->d_name.hash);

                hlist_bl_lock(b);
                __hlist_bl_del(&dentry->d_hash);
                dentry->d_hash.pprev = NULL;
                hlist_bl_unlock(b);
        }
}

/**
 * d_drop - drop a dentry
 * @dentry: dentry to drop
 *
 * d_drop() unhashes the entry from the parent dentry hashes, so that it won't
 * be found through a VFS lookup any more. Note that this is different from
 * deleting the dentry - d_delete will try to mark the dentry negative if
 * possible, giving a successful _negative_ lookup, while d_drop will
 * just make the cache lookup fail.
 *
 * d_drop() is used mainly for stuff that wants to invalidate a dentry for some
 * reason (NFS timeouts or autofs deletes).
 *
 * __d_drop requires dentry->d_lock.
 */
void __d_drop(struct dentry *dentry)
{
        if (!d_unhashed(dentry)) {
                __d_shrink(dentry);
                dentry_rcuwalk_barrier(dentry);
        }
}
EXPORT_SYMBOL(__d_drop);

void d_drop(struct dentry *dentry)
{
        spin_lock(&dentry->d_lock);
        __d_drop(dentry);
        spin_unlock(&dentry->d_lock);
}
EXPORT_SYMBOL(d_drop);

/*
 * d_clear_need_lookup - drop a dentry from cache and clear the need lookup flag
 * @dentry: dentry to drop
 *
 * This is called when we do a lookup on a placeholder dentry that needed to be
 * looked up.  The dentry should have been hashed in order for it to be found by
 * the lookup code, but now needs to be unhashed while we do the actual lookup
 * and clear the DCACHE_NEED_LOOKUP flag.
 */
void d_clear_need_lookup(struct dentry *dentry)
{
        spin_lock(&dentry->d_lock);
        __d_drop(dentry);
        dentry->d_flags &= ~DCACHE_NEED_LOOKUP;
        spin_unlock(&dentry->d_lock);
}
EXPORT_SYMBOL(d_clear_need_lookup);

/*
 * Finish off a dentry we've decided to kill.
 * dentry->d_lock must be held, returns with it unlocked.
 * If ref is non-zero, then decrement the refcount too.
 * Returns dentry requiring refcount drop, or NULL if we're done.
 */
static inline struct dentry *dentry_kill(struct dentry *dentry, int ref)
        __releases(dentry->d_lock)
{
        struct inode *inode;
        struct dentry *parent;

        inode = dentry->d_inode;
        if (inode && !spin_trylock(&inode->i_lock)) {
relock:
                spin_unlock(&dentry->d_lock);
                cpu_relax();
                return dentry; /* try again with same dentry */
        }
        if (IS_ROOT(dentry))
                parent = NULL;
        else
                parent = dentry->d_parent;
        if (parent && !spin_trylock(&parent->d_lock)) {
                if (inode)
                        spin_unlock(&inode->i_lock);
                goto relock;
        }

        if (ref)
                dentry->d_count--;
        /*
         * if dentry was on the d_lru list delete it from there.
         * inform the fs via d_prune that this dentry is about to be
         * unhashed and destroyed.
         */
        dentry_lru_prune(dentry);
        /* if it was on the hash then remove it */
        __d_drop(dentry);
        return d_kill(dentry, parent);
}

/* 
 * 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.
 */
void dput(struct dentry *dentry)
{
        if (!dentry)
                return;

repeat:
        if (dentry->d_count == 1)
                might_sleep();
        spin_lock(&dentry->d_lock);
        BUG_ON(!dentry->d_count);
        if (dentry->d_count > 1) {
                dentry->d_count--;
                spin_unlock(&dentry->d_lock);
                return;
        }

        if (dentry->d_flags & DCACHE_OP_DELETE) {
                if (dentry->d_op->d_delete(dentry))
                        goto kill_it;
        }

        /* Unreachable? Get rid of it */
        if (d_unhashed(dentry))
                goto kill_it;

        /*
         * If this dentry needs lookup, don't set the referenced flag so that it
         * is more likely to be cleaned up by the dcache shrinker in case of
         * memory pressure.
         */
        if (!d_need_lookup(dentry))
                dentry->d_flags |= DCACHE_REFERENCED;
        dentry_lru_add(dentry);

        dentry->d_count--;
        spin_unlock(&dentry->d_lock);
        return;

kill_it:
        dentry = dentry_kill(dentry, 1);
        if (dentry)
                goto repeat;
}
EXPORT_SYMBOL(dput);

/**
 * 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(&dentry->d_lock);
        if (d_unhashed(dentry)) {
                spin_unlock(&dentry->d_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(&dentry->d_lock);
                shrink_dcache_parent(dentry);
                spin_lock(&dentry->d_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).
         * We also need to leave mountpoints alone,
         * directory or not.
         */
        if (dentry->d_count > 1 && dentry->d_inode) {
                if (S_ISDIR(dentry->d_inode->i_mode) || d_mountpoint(dentry)) {
                        spin_unlock(&dentry->d_lock);
                        return -EBUSY;
                }
        }

        __d_drop(dentry);
        spin_unlock(&dentry->d_lock);
        return 0;
}
EXPORT_SYMBOL(d_invalidate);

/* This must be called with d_lock held */
static inline void __dget_dlock(struct dentry *dentry)
{
        dentry->d_count++;
}

static inline void __dget(struct dentry *dentry)
{
        spin_lock(&dentry->d_lock);
        __dget_dlock(dentry);
        spin_unlock(&dentry->d_lock);
}

struct dentry *dget_parent(struct dentry *dentry)
{
        struct dentry *ret;

repeat:
        /*
         * Don't need rcu_dereference because we re-check it was correct under
         * the lock.
         */
        rcu_read_lock();
        ret = dentry->d_parent;
        spin_lock(&ret->d_lock);
        if (unlikely(ret != dentry->d_parent)) {
                spin_unlock(&ret->d_lock);
                rcu_read_unlock();
                goto repeat;
        }
        rcu_read_unlock();
        BUG_ON(!ret->d_count);
        ret->d_count++;
        spin_unlock(&ret->d_lock);
        return ret;
}
EXPORT_SYMBOL(dget_parent);

/**
 * 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 dentry *alias, *discon_alias;

again:
        discon_alias = NULL;
        list_for_each_entry(alias, &inode->i_dentry, d_alias) {
                spin_lock(&alias->d_lock);
                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_dlock(alias);
                                spin_unlock(&alias->d_lock);
                                return alias;
                        }
                }
                spin_unlock(&alias->d_lock);
        }
        if (discon_alias) {
                alias = discon_alias;
                spin_lock(&alias->d_lock);
                if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
                        if (IS_ROOT(alias) &&
                            (alias->d_flags & DCACHE_DISCONNECTED)) {
                                __dget_dlock(alias);
                                spin_unlock(&alias->d_lock);
                                return alias;
                        }
                }
                spin_unlock(&alias->d_lock);
                goto again;
        }
        return NULL;
}

struct dentry *d_find_alias(struct inode *inode)
{
        struct dentry *de = NULL;

        if (!list_empty(&inode->i_dentry)) {
                spin_lock(&inode->i_lock);
                de = __d_find_alias(inode, 0);
                spin_unlock(&inode->i_lock);
        }
        return de;
}
EXPORT_SYMBOL(d_find_alias);

/*
 *      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(&inode->i_lock);
        list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
                spin_lock(&dentry->d_lock);
                if (!dentry->d_count) {
                        __dget_dlock(dentry);
                        __d_drop(dentry);
                        spin_unlock(&dentry->d_lock);
                        spin_unlock(&inode->i_lock);
                        dput(dentry);
                        goto restart;
                }
                spin_unlock(&dentry->d_lock);
        }
        spin_unlock(&inode->i_lock);
}
EXPORT_SYMBOL(d_prune_aliases);

/*
 * Try to throw away a dentry - free the inode, dput the parent.
 * Requires dentry->d_lock is held, and dentry->d_count == 0.
 * Releases dentry->d_lock.
 *
 * This may fail if locks cannot be acquired no problem, just try again.
 */
static void try_prune_one_dentry(struct dentry *dentry)
        __releases(dentry->d_lock)
{
        struct dentry *parent;

        parent = dentry_kill(dentry, 0);
        /*
         * If dentry_kill returns NULL, we have nothing more to do.
         * if it returns the same dentry, trylocks failed. In either
         * case, just loop again.
         *
         * Otherwise, we need to prune ancestors too. This is necessary
         * to prevent quadratic behavior of shrink_dcache_parent(), but
         * is also expected to be beneficial in reducing dentry cache
         * fragmentation.
         */
        if (!parent)
                return;
        if (parent == dentry)
                return;

        /* Prune ancestors. */
        dentry = parent;
        while (dentry) {
                spin_lock(&dentry->d_lock);
                if (dentry->d_count > 1) {
                        dentry->d_count--;
                        spin_unlock(&dentry->d_lock);
                        return;
                }
                dentry = dentry_kill(dentry, 1);
        }
}

static void shrink_dentry_list(struct list_head *list)
{
        struct dentry *dentry;

        rcu_read_lock();
        for (;;) {
                dentry = list_entry_rcu(list->prev, struct dentry, d_lru);
                if (&dentry->d_lru == list)
                        break; /* empty */
                spin_lock(&dentry->d_lock);
                if (dentry != list_entry(list->prev, struct dentry, d_lru)) {
                        spin_unlock(&dentry->d_lock);
                        continue;
                }

                /*
                 * We found an inuse dentry which was not removed from
                 * the LRU because of laziness during lookup.  Do not free
                 * it - just keep it off the LRU list.
                 */
                if (dentry->d_count) {
                        dentry_lru_del(dentry);
                        spin_unlock(&dentry->d_lock);
                        continue;
                }

                rcu_read_unlock();

                try_prune_one_dentry(dentry);

                rcu_read_lock();
        }
        rcu_read_unlock();
}

/**
 * __shrink_dcache_sb - shrink the dentry LRU on a given superblock
 * @sb:         superblock to shrink dentry LRU.
 * @count:      number of entries to prune
 * @flags:      flags to control the dentry processing
 *
 * If flags contains DCACHE_REFERENCED reference dentries will not be pruned.
 */
static void __shrink_dcache_sb(struct super_block *sb, int count, int flags)
{
        struct dentry *dentry;
        LIST_HEAD(referenced);
        LIST_HEAD(tmp);

relock:
        spin_lock(&dcache_lru_lock);
        while (!list_empty(&sb->s_dentry_lru)) {
                dentry = list_entry(sb->s_dentry_lru.prev,
                                struct dentry, d_lru);
                BUG_ON(dentry->d_sb != sb);

                if (!spin_trylock(&dentry->d_lock)) {
                        spin_unlock(&dcache_lru_lock);
                        cpu_relax();
                        goto relock;
                }

                /*
                 * If we are honouring the DCACHE_REFERENCED flag and the
                 * dentry has this flag set, don't free it.  Clear the flag
                 * and put it back on the LRU.
                 */
                if (flags & DCACHE_REFERENCED &&
                                dentry->d_flags & DCACHE_REFERENCED) {
                        dentry->d_flags &= ~DCACHE_REFERENCED;
                        list_move(&dentry->d_lru, &referenced);
                        spin_unlock(&dentry->d_lock);
                } else {
                        list_move_tail(&dentry->d_lru, &tmp);
                        spin_unlock(&dentry->d_lock);
                        if (!--count)
                                break;
                }
                cond_resched_lock(&dcache_lru_lock);
        }
        if (!list_empty(&referenced))
                list_splice(&referenced, &sb->s_dentry_lru);
        spin_unlock(&dcache_lru_lock);

        shrink_dentry_list(&tmp);
}

/**
 * prune_dcache_sb - shrink the dcache
 * @sb: superblock
 * @nr_to_scan: number of entries to try to free
 *
 * Attempt to shrink the superblock dcache LRU by @nr_to_scan entries. This is
 * done when we need more memory an called from the superblock shrinker
 * function.
 *
 * This function may fail to free any resources if all the dentries are in
 * use.
 */
void prune_dcache_sb(struct super_block *sb, int nr_to_scan)
{
        __shrink_dcache_sb(sb, nr_to_scan, DCACHE_REFERENCED);
}

/**
 * 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)
{
        LIST_HEAD(tmp);

        spin_lock(&dcache_lru_lock);
        while (!list_empty(&sb->s_dentry_lru)) {
                list_splice_init(&sb->s_dentry_lru, &tmp);
                spin_unlock(&dcache_lru_lock);
                shrink_dentry_list(&tmp);
                spin_lock(&dcache_lru_lock);
        }
        spin_unlock(&dcache_lru_lock);
}
EXPORT_SYMBOL(shrink_dcache_sb);

/*
 * 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;

        BUG_ON(!IS_ROOT(dentry));

        for (;;) {
                /* descend to the first leaf in the current subtree */
                while (!list_empty(&dentry->d_subdirs))
                        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;

                        /*
                         * remove the dentry from the lru, and inform
                         * the fs that this dentry is about to be
                         * unhashed and destroyed.
                         */
                        dentry_lru_prune(dentry);
                        __d_shrink(dentry);

                        if (dentry->d_count != 0) {
                                printk(KERN_ERR
                                       "BUG: Dentry %p{i=%lx,n=%s}"
                                       " still in use (%d)"
                                       " [unmount of %s %s]\n",
                                       dentry,
                                       dentry->d_inode ?
                                       dentry->d_inode->i_ino : 0UL,
                                       dentry->d_name.name,
                                       dentry->d_count,
                                       dentry->d_sb->s_type->name,
                                       dentry->d_sb->s_id);
                                BUG();
                        }

                        if (IS_ROOT(dentry)) {
                                parent = NULL;
                                list_del(&dentry->d_u.d_child);
                        } else {
                                parent = dentry->d_parent;
                                parent->d_count--;
                                list_del(&dentry->d_u.d_child);
                        }

                        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)
                                return;
                        dentry = parent;
                } while (list_empty(&dentry->d_subdirs));

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

/*
 * destroy the dentries attached to a superblock on unmounting
 * - we don't need to use dentry->d_lock 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;
        dentry->d_count--;
        shrink_dcache_for_umount_subtree(dentry);

        while (!hlist_bl_empty(&sb->s_anon)) {
                dentry = hlist_bl_entry(hlist_bl_first(&sb->s_anon), struct dentry, d_hash);
                shrink_dcache_for_umount_subtree(dentry);
        }
}

/*
 * This tries to ascend one level of parenthood, but
 * we can race with renaming, so we need to re-check
 * the parenthood after dropping the lock and check
 * that the sequence number still matches.
 */
static struct dentry *try_to_ascend(struct dentry *old, int locked, unsigned seq)
{
        struct dentry *new = old->d_parent;

        rcu_read_lock();
        spin_unlock(&old->d_lock);
        spin_lock(&new->d_lock);

        /*
         * might go back up the wrong parent if we have had a rename
         * or deletion
         */
        if (new != old->d_parent ||
                 (old->d_flags & DCACHE_DISCONNECTED) ||
                 (!locked && read_seqretry(&rename_lock, seq))) {
                spin_unlock(&new->d_lock);
                new = NULL;
        }
        rcu_read_unlock();
        return new;
}


/*
 * 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;
        struct list_head *next;
        unsigned seq;
        int locked = 0;

        seq = read_seqbegin(&rename_lock);
again:
        this_parent = parent;

        if (d_mountpoint(parent))
                goto positive;
        spin_lock(&this_parent->d_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;

                spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
                /* Have we found a mount point ? */
                if (d_mountpoint(dentry)) {
                        spin_unlock(&dentry->d_lock);
                        spin_unlock(&this_parent->d_lock);
                        goto positive;
                }
                if (!list_empty(&dentry->d_subdirs)) {
                        spin_unlock(&this_parent->d_lock);
                        spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
                        this_parent = dentry;
                        spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
                        goto repeat;
                }
                spin_unlock(&dentry->d_lock);
        }
        /*
         * All done at this level ... ascend and resume the search.
         */
        if (this_parent != parent) {
                struct dentry *child = this_parent;
                this_parent = try_to_ascend(this_parent, locked, seq);
                if (!this_parent)
                        goto rename_retry;
                next = child->d_u.d_child.next;
                goto resume;
        }
        spin_unlock(&this_parent->d_lock);
        if (!locked && read_seqretry(&rename_lock, seq))
                goto rename_retry;
        if (locked)
                write_sequnlock(&rename_lock);
        return 0; /* No mount points found in tree */
positive:
        if (!locked && read_seqretry(&rename_lock, seq))
                goto rename_retry;
        if (locked)
                write_sequnlock(&rename_lock);
        return 1;

rename_retry:
        locked = 1;
        write_seqlock(&rename_lock);
        goto again;
}
EXPORT_SYMBOL(have_submounts);

/*
 * 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;
        struct list_head *next;
        unsigned seq;
        int found = 0;
        int locked = 0;

        seq = read_seqbegin(&rename_lock);
again:
        this_parent = parent;
        spin_lock(&this_parent->d_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;

                spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);

                /* 
                 * move only zero ref count dentries to the end 
                 * of the unused list for prune_dcache
                 */
                if (!dentry->d_count) {
                        dentry_lru_move_tail(dentry);
                        found++;
                } else {
                        dentry_lru_del(dentry);
                }

                /*
                 * 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()) {
                        spin_unlock(&dentry->d_lock);
                        goto out;
                }

                /*
                 * Descend a level if the d_subdirs list is non-empty.
                 */
                if (!list_empty(&dentry->d_subdirs)) {
                        spin_unlock(&this_parent->d_lock);
                        spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
                        this_parent = dentry;
                        spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
                        goto repeat;
                }

                spin_unlock(&dentry->d_lock);
        }
        /*
         * All done at this level ... ascend and resume the search.
         */
        if (this_parent != parent) {
                struct dentry *child = this_parent;
                this_parent = try_to_ascend(this_parent, locked, seq);
                if (!this_parent)
                        goto rename_retry;
                next = child->d_u.d_child.next;
                goto resume;
        }
out:
        spin_unlock(&this_parent->d_lock);
        if (!locked && read_seqretry(&rename_lock, seq))
                goto rename_retry;
        if (locked)
                write_sequnlock(&rename_lock);
        return found;

rename_retry:
        if (found)
                return found;
        locked = 1;
        write_seqlock(&rename_lock);
        goto again;
}

/**
 * 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)
{
        struct super_block *sb = parent->d_sb;
        int found;

        while ((found = select_parent(parent)) != 0)
                __shrink_dcache_sb(sb, found, 0);
}
EXPORT_SYMBOL(shrink_dcache_parent);

/**
 * __d_alloc    -       allocate a dcache entry
 * @sb: filesystem it will belong to
 * @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 super_block *sb, 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;

        dentry->d_count = 1;
        dentry->d_flags = 0;
        spin_lock_init(&dentry->d_lock);
        seqcount_init(&dentry->d_seq);
        dentry->d_inode = NULL;
        dentry->d_parent = dentry;
        dentry->d_sb = sb;
        dentry->d_op = NULL;
        dentry->d_fsdata = NULL;
        INIT_HLIST_BL_NODE(&dentry->d_hash);
        INIT_LIST_HEAD(&dentry->d_lru);
        INIT_LIST_HEAD(&dentry->d_subdirs);
        INIT_LIST_HEAD(&dentry->d_alias);
        INIT_LIST_HEAD(&dentry->d_u.d_child);
        d_set_d_op(dentry, dentry->d_sb->s_d_op);

        this_cpu_inc(nr_dentry);

        return dentry;
}

/**
 * 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 = __d_alloc(parent->d_sb, name);
        if (!dentry)
                return NULL;

        spin_lock(&parent->d_lock);
        /*
         * don't need child lock because it is not subject
         * to concurrency here
         */
        __dget_dlock(parent);
        dentry->d_parent = parent;
        list_add(&dentry->d_u.d_child, &parent->d_subdirs);
        spin_unlock(&parent->d_lock);

        return dentry;
}
EXPORT_SYMBOL(d_alloc);

struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
{
        struct dentry *dentry = __d_alloc(sb, name);
        if (dentry)
                dentry->d_flags |= DCACHE_DISCONNECTED;
        return dentry;
}
EXPORT_SYMBOL(d_alloc_pseudo);

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);
}
EXPORT_SYMBOL(d_alloc_name);

void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
{
        WARN_ON_ONCE(dentry->d_op);
        WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH  |
                                DCACHE_OP_COMPARE       |
                                DCACHE_OP_REVALIDATE    |
                                DCACHE_OP_DELETE ));
        dentry->d_op = op;
        if (!op)
                return;
        if (op->d_hash)
                dentry->d_flags |= DCACHE_OP_HASH;
        if (op->d_compare)
                dentry->d_flags |= DCACHE_OP_COMPARE;
        if (op->d_revalidate)
                dentry->d_flags |= DCACHE_OP_REVALIDATE;
        if (op->d_delete)
                dentry->d_flags |= DCACHE_OP_DELETE;
        if (op->d_prune)
                dentry->d_flags |= DCACHE_OP_PRUNE;

}
EXPORT_SYMBOL(d_set_d_op);

static void __d_instantiate(struct dentry *dentry, struct inode *inode)
{
        spin_lock(&dentry->d_lock);
        if (inode) {
                if (unlikely(IS_AUTOMOUNT(inode)))
                        dentry->d_flags |= DCACHE_NEED_AUTOMOUNT;
                list_add(&dentry->d_alias, &inode->i_dentry);
        }
        dentry->d_inode = inode;
        dentry_rcuwalk_barrier(dentry);
        spin_unlock(&dentry->d_lock);
        fsnotify_d_instantiate(dentry, inode);
}

/**
 * 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));
        if (inode)
                spin_lock(&inode->i_lock);
        __d_instantiate(entry, inode);
        if (inode)
                spin_unlock(&inode->i_lock);
        security_d_instantiate(entry, inode);
}
EXPORT_SYMBOL(d_instantiate);

/**
 * 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) {
                __d_instantiate(entry, NULL);
                return NULL;
        }

        list_for_each_entry(alias, &inode->i_dentry, d_alias) {
                struct qstr *qstr = &alias->d_name;

                /*
                 * Don't need alias->d_lock here, because aliases with
                 * d_parent == entry->d_parent are not subject to name or
                 * parent changes, because the parent inode i_mutex is held.
                 */
                if (qstr->hash != hash)
                        continue;
                if (alias->d_parent != entry->d_parent)
                        continue;
                if (dentry_cmp(qstr->name, qstr->len, name, len))
                        continue;
                __dget(alias);
                return alias;
        }

        __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));

        if (inode)
                spin_lock(&inode->i_lock);
        result = __d_instantiate_unique(entry, inode);
        if (inode)
                spin_unlock(&inode->i_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(root_inode->i_sb, &name);
                if (res)
                        d_instantiate(res, root_inode);
        }
        return res;
}
EXPORT_SYMBOL(d_alloc_root);

static struct dentry * __d_find_any_alias(struct inode *inode)
{
        struct dentry *alias;

        if (list_empty(&inode->i_dentry))
                return NULL;
        alias = list_first_entry(&inode->i_dentry, struct dentry, d_alias);
        __dget(alias);
        return alias;
}

static struct dentry * d_find_any_alias(struct inode *inode)
{
        struct dentry *de;

        spin_lock(&inode->i_lock);
        de = __d_find_any_alias(inode);
        spin_unlock(&inode->i_lock);
        return de;
}


/**
 * d_obtain_alias - find or allocate a dentry for a given inode
 * @inode: inode to allocate the dentry for
 *
 * Obtain a dentry for an inode resulting from NFS filehandle conversion or
 * similar open by handle operations.  The returned dentry may be anonymous,
 * or may have a full name (if the inode was already in the cache).
 *
 * 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.  In case of an error the reference on the inode is released.
 * To make it easier to use in export operations a %NULL or IS_ERR inode may
 * be passed in and will be the error will be propagate to the return value,
 * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
 */
struct dentry *d_obtain_alias(struct inode *inode)
{
        static const struct qstr anonstring = { .name = "" };
        struct dentry *tmp;
        struct dentry *res;

        if (!inode)
                return ERR_PTR(-ESTALE);
        if (IS_ERR(inode))
                return ERR_CAST(inode);

        res = d_find_any_alias(inode);
        if (res)
                goto out_iput;

        tmp = __d_alloc(inode->i_sb, &anonstring);
        if (!tmp) {
                res = ERR_PTR(-ENOMEM);
                goto out_iput;
        }

        spin_lock(&inode->i_lock);
        res = __d_find_any_alias(inode);
        if (res) {
                spin_unlock(&inode->i_lock);
                dput(tmp);
                goto out_iput;
        }

        /* attach a disconnected dentry */
        spin_lock(&tmp->d_lock);
        tmp->d_inode = inode;
        tmp->d_flags |= DCACHE_DISCONNECTED;
        list_add(&tmp->d_alias, &inode->i_dentry);
        hlist_bl_lock(&tmp->d_sb->s_anon);
        hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon);
        hlist_bl_unlock(&tmp->d_sb->s_anon);
        spin_unlock(&tmp->d_lock);
        spin_unlock(&inode->i_lock);
        security_d_instantiate(tmp, inode);

        return tmp;

 out_iput:
        if (res && !IS_ERR(res))
                security_d_instantiate(res, inode);
        iput(inode);
        return res;
}
EXPORT_SYMBOL(d_obtain_alias);

/**
 * 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 (IS_ERR(inode))
                return ERR_CAST(inode);

        if (inode && S_ISDIR(inode->i_mode)) {
                spin_lock(&inode->i_lock);
                new = __d_find_alias(inode, 1);
                if (new) {
                        BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));
                        spin_unlock(&inode->i_lock);
                        security_d_instantiate(new, inode);
                        d_move(new, dentry);
                        iput(inode);
                } else {
                        /* already taking inode->i_lock, so d_add() by hand */
                        __d_instantiate(dentry, inode);
                        spin_unlock(&inode->i_lock);
                        security_d_instantiate(dentry, inode);
                        d_rehash(dentry);
                }
        } else
                d_add(dentry, inode);
        return new;
}
EXPORT_SYMBOL(d_splice_alias);

/**
 * d_add_ci - lookup or allocate new dentry with case-exact name
 * @inode:  the inode case-insensitive lookup has found
 * @dentry: the negative dentry that was passed to the parent's lookup func
 * @name:   the case-exact name to be associated with the returned dentry
 *
 * This is to avoid filling the dcache with case-insensitive names to the
 * same inode, only the actual correct case is stored in the dcache for
 * case-insensitive filesystems.
 *
 * For a case-insensitive lookup match and if the the case-exact dentry
 * already exists in in the dcache, use it and return it.
 *
 * If no entry exists with the exact case name, allocate new dentry with
 * the exact case, and return the spliced entry.
 */
struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
                        struct qstr *name)
{
        int error;
        struct dentry *found;
        struct dentry *new;

        /*
         * First check if a dentry matching the name already exists,
         * if not go ahead and create it now.
         */
        found = d_hash_and_lookup(dentry->d_parent, name);
        if (!found) {
                new = d_alloc(dentry->d_parent, name);
                if (!new) {
                        error = -ENOMEM;
                        goto err_out;
                }

                found = d_splice_alias(inode, new);
                if (found) {
                        dput(new);
                        return found;
                }
                return new;
        }

        /*
         * If a matching dentry exists, and it's not negative use it.
         *
         * Decrement the reference count to balance the iget() done
         * earlier on.
         */
        if (found->d_inode) {
                if (unlikely(found->d_inode != inode)) {
                        /* This can't happen because bad inodes are unhashed. */
                        BUG_ON(!is_bad_inode(inode));
                        BUG_ON(!is_bad_inode(found->d_inode));
                }
                iput(inode);
                return found;
        }

        /*
         * We are going to instantiate this dentry, unhash it and clear the
         * lookup flag so we can do that.
         */
        if (unlikely(d_need_lookup(found)))
                d_clear_need_lookup(found);

        /*
         * Negative dentry: instantiate it unless the inode is a directory and
         * already has a dentry.
         */
        new = d_splice_alias(inode, found);
        if (new) {
                dput(found);
                found = new;
        }
        return found;

err_out:
        iput(inode);
        return ERR_PTR(error);
}
EXPORT_SYMBOL(d_add_ci);

/**
 * __d_lookup_rcu - search for a dentry (racy, store-free)
 * @parent: parent dentry
 * @name: qstr of name we wish to find
 * @seq: returns d_seq value at the point where the dentry was found
 * @inode: returns dentry->d_inode when the inode was found valid.
 * Returns: dentry, or NULL
 *
 * __d_lookup_rcu is the dcache lookup function for rcu-walk name
 * resolution (store-free path walking) design described in
 * Documentation/filesystems/path-lookup.txt.
 *
 * This is not to be used outside core vfs.
 *
 * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
 * held, and rcu_read_lock held. The returned dentry must not be stored into
 * without taking d_lock and checking d_seq sequence count against @seq
 * returned here.
 *
 * A refcount may be taken on the found dentry with the __d_rcu_to_refcount
 * function.
 *
 * Alternatively, __d_lookup_rcu may be called again to look up the child of
 * the returned dentry, so long as its parent's seqlock is checked after the
 * child is looked up. Thus, an interlocking stepping of sequence lock checks
 * is formed, giving integrity down the path walk.
 */
struct dentry *__d_lookup_rcu(struct dentry *parent, struct qstr *name,
                                unsigned *seq, struct inode **inode)
{
        unsigned int len = name->len;
        unsigned int hash = name->hash;
        const unsigned char *str = name->name;
        struct hlist_bl_head *b = d_hash(parent, hash);
        struct hlist_bl_node *node;
        struct dentry *dentry;

        /*
         * Note: There is significant duplication with __d_lookup_rcu which is
         * required to prevent single threaded performance regressions
         * especially on architectures where smp_rmb (in seqcounts) are costly.
         * Keep the two functions in sync.
         */

        /*
         * The hash list is protected using RCU.
         *
         * Carefully use d_seq when comparing a candidate dentry, to avoid
         * races with d_move().
         *
         * It is possible that concurrent renames can mess up our list
         * walk here and result in missing our dentry, resulting in the
         * false-negative result. d_lookup() protects against concurrent
         * renames using rename_lock seqlock.
         *
         * See Documentation/filesystems/path-lookup.txt for more details.
         */
        hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
                struct inode *i;
                const char *tname;
                int tlen;

                if (dentry->d_name.hash != hash)
                        continue;

seqretry:
                *seq = read_seqcount_begin(&dentry->d_seq);
                if (dentry->d_parent != parent)
                        continue;
                if (d_unhashed(dentry))
                        continue;
                tlen = dentry->d_name.len;
                tname = dentry->d_name.name;
                i = dentry->d_inode;
                prefetch(tname);
                /*
                 * This seqcount check is required to ensure name and
                 * len are loaded atomically, so as not to walk off the
                 * edge of memory when walking. If we could load this
                 * atomically some other way, we could drop this check.
                 */
                if (read_seqcount_retry(&dentry->d_seq, *seq))
                        goto seqretry;
                if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
                        if (parent->d_op->d_compare(parent, *inode,
                                                dentry, i,
                                                tlen, tname, name))
                                continue;
                } else {
                        if (dentry_cmp(tname, tlen, str, len))
                                continue;
                }
                /*
                 * No extra seqcount check is required after the name
                 * compare. The caller must perform a seqcount check in
                 * order to do anything useful with the returned dentry
                 * anyway.
                 */
                *inode = i;
                return dentry;
        }
        return NULL;
}

/**
 * d_lookup - search for a dentry
 * @parent: parent dentry
 * @name: qstr of name we wish to find
 * Returns: dentry, or NULL
 *
 * d_lookup 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 dput to free the entry when it has
 * finished using it. %NULL is returned if the dentry does not exist.
 */
struct dentry *d_lookup(struct dentry *parent, struct qstr *name)
{
        struct dentry *dentry;
        unsigned seq;

        do {
                seq = read_seqbegin(&rename_lock);
                dentry = __d_lookup(parent, name);
                if (dentry)
                        break;
        } while (read_seqretry(&rename_lock, seq));
        return dentry;
}
EXPORT_SYMBOL(d_lookup);

/**
 * __d_lookup - search for a dentry (racy)
 * @parent: parent dentry
 * @name: qstr of name we wish to find
 * Returns: dentry, or NULL
 *
 * __d_lookup is like d_lookup, however it may (rarely) return a
 * false-negative result due to unrelated rename activity.
 *
 * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
 * however it must be used carefully, eg. with a following d_lookup in
 * the case of failure.
 *
 * __d_lookup callers must be commented.
 */
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_bl_head *b = d_hash(parent, hash);
        struct hlist_bl_node *node;
        struct dentry *found = NULL;
        struct dentry *dentry;

        /*
         * Note: There is significant duplication with __d_lookup_rcu which is
         * required to prevent single threaded performance regressions
         * especially on architectures where smp_rmb (in seqcounts) are costly.
         * Keep the two functions in sync.
         */

        /*
         * The hash list is protected using RCU.
         *
         * Take d_lock when comparing a candidate dentry, to avoid races
         * with d_move().
         *
         * It is possible that concurrent renames can mess up our list
         * walk here and result in missing our dentry, resulting in the
         * false-negative result. d_lookup() protects against concurrent
         * renames using rename_lock seqlock.
         *
         * See Documentation/filesystems/path-lookup.txt for more details.
         */
        rcu_read_lock();
        
        hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
                const char *tname;
                int tlen;

                if (dentry->d_name.hash != hash)
                        continue;

                spin_lock(&dentry->d_lock);
                if (dentry->d_parent != parent)
                        goto next;
                if (d_unhashed(dentry))
                        goto next;

                /*
                 * It is safe to compare names since d_move() cannot
                 * change the qstr (protected by d_lock).
                 */
                tlen = dentry->d_name.len;
                tname = dentry->d_name.name;
                if (parent->d_flags & DCACHE_OP_COMPARE) {
                        if (parent->d_op->d_compare(parent, parent->d_inode,
                                                dentry, dentry->d_inode,
                                                tlen, tname, name))
                                goto next;
                } else {
                        if (dentry_cmp(tname, tlen, str, len))
                                goto next;
                }

                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_flags & DCACHE_OP_HASH) {
                if (dir->d_op->d_hash(dir, dir->d_inode, name) < 0)
                        goto out;
        }
        dentry = d_lookup(dir, name);
out:
        return dentry;
}

/**
 * d_validate - verify dentry provided from insecure source (deprecated)
 * @dentry: The dentry alleged to be valid child of @dparent
 * @dparent: The parent dentry (known to be valid)
 *
 * 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.
 *
 * This function is slow for big directories, and deprecated, do not use it.
 */
int d_validate(struct dentry *dentry, struct dentry *dparent)
{
        struct dentry *child;

        spin_lock(&dparent->d_lock);
        list_for_each_entry(child, &dparent->d_subdirs, d_u.d_child) {
                if (dentry == child) {
                        spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
                        __dget_dlock(dentry);
                        spin_unlock(&dentry->d_lock);
                        spin_unlock(&dparent->d_lock);
                        return 1;
                }
        }
        spin_unlock(&dparent->d_lock);

        return 0;
}
EXPORT_SYMBOL(d_validate);

/*
 * 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)
{
        struct inode *inode;
        int isdir = 0;
        /*
         * Are we the only user?
         */
again:
        spin_lock(&dentry->d_lock);
        inode = dentry->d_inode;
        isdir = S_ISDIR(inode->i_mode);
        if (dentry->d_count == 1) {
                if (inode && !spin_trylock(&inode->i_lock)) {
                        spin_unlock(&dentry->d_lock);
                        cpu_relax();
                        goto again;
                }
                dentry->d_flags &= ~DCACHE_CANT_MOUNT;
                dentry_unlink_inode(dentry);
                fsnotify_nameremove(dentry, isdir);
                return;
        }