/*
 * 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/export.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 <linux/list_lru.h>
#include "internal.h"
#include "mount.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)
 * dentry->d_sb->s_dentry_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
 *     dentry->d_sb->s_dentry_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);

__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.
 */

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(const struct dentry *parent,
                                        unsigned int hash)
{
        hash += (unsigned long) parent / L1_CACHE_BYTES;
        hash = hash + (hash >> d_hash_shift);
        return dentry_hashtable + (hash & d_hash_mask);
}

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

static DEFINE_PER_CPU(long, nr_dentry);
static DEFINE_PER_CPU(long, nr_dentry_unused);

#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)

/*
 * Here we resort to our own counters instead of using generic per-cpu counters
 * for consistency with what the vfs inode code does. We are expected to harvest
 * better code and performance by having our own specialized counters.
 *
 * Please note that the loop is done over all possible CPUs, not over all online
 * CPUs. The reason for this is that we don't want to play games with CPUs going
 * on and off. If one of them goes off, we will just keep their counters.
 *
 * glommer: See cffbc8a for details, and if you ever intend to change this,
 * please update all vfs counters to match.
 */
static long get_nr_dentry(void)
{
        int i;
        long sum = 0;
        for_each_possible_cpu(i)
                sum += per_cpu(nr_dentry, i);
        return sum < 0 ? 0 : sum;
}

static long get_nr_dentry_unused(void)
{
        int i;
        long sum = 0;
        for_each_possible_cpu(i)
                sum += per_cpu(nr_dentry_unused, 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();
        dentry_stat.nr_unused = get_nr_dentry_unused();
        return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
}
#endif

/*
 * Compare 2 name strings, return 0 if they match, otherwise non-zero.
 * The strings are both count bytes long, and count is non-zero.
 */
#ifdef CONFIG_DCACHE_WORD_ACCESS

#include <asm/word-at-a-time.h>
/*
 * NOTE! 'cs' and 'scount' come from a dentry, so it has a
 * aligned allocation for this particular component. We don't
 * strictly need the load_unaligned_zeropad() safety, but it
 * doesn't hurt either.
 *
 * In contrast, 'ct' and 'tcount' can be from a pathname, and do
 * need the careful unaligned handling.
 */
static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
{
        unsigned long a,b,mask;

        for (;;) {
                a = *(unsigned long *)cs;
                b = load_unaligned_zeropad(ct);
                if (tcount < sizeof(unsigned long))
                        break;
                if (unlikely(a != b))
                        return 1;
                cs += sizeof(unsigned long);
                ct += sizeof(unsigned long);
                tcount -= sizeof(unsigned long);
                if (!tcount)
                        return 0;
        }
        mask = bytemask_from_count(tcount);
        return unlikely(!!((a ^ b) & mask));
}

#else

static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
{
        do {
                if (*cs != *ct)
                        return 1;
                cs++;
                ct++;
                tcount--;
        } while (tcount);
        return 0;
}

#endif

static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
{
        const unsigned char *cs;
        /*
         * Be careful about RCU walk racing with rename:
         * use ACCESS_ONCE to fetch the name pointer.
         *
         * NOTE! Even if a rename will mean that the length
         * was not loaded atomically, we don't care. The
         * RCU walk will check the sequence count eventually,
         * and catch it. And we won't overrun the buffer,
         * because we're reading the name pointer atomically,
         * and a dentry name is guaranteed to be properly
         * terminated with a NUL byte.
         *
         * End result: even if 'len' is wrong, we'll exit
         * early because the data cannot match (there can
         * be no NUL in the ct/tcount data)
         */
        cs = ACCESS_ONCE(dentry->d_name.name);
        smp_read_barrier_depends();
        return dentry_string_cmp(cs, ct, tcount);
}

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

        WARN_ON(!hlist_unhashed(&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((int)dentry->d_lockref.count > 0);
        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;
                hlist_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;
        __d_clear_type(dentry);
        dentry->d_inode = NULL;
        hlist_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);
}

/*
 * The DCACHE_LRU_LIST bit is set whenever the 'd_lru' entry
 * is in use - which includes both the "real" per-superblock
 * LRU list _and_ the DCACHE_SHRINK_LIST use.
 *
 * The DCACHE_SHRINK_LIST bit is set whenever the dentry is
 * on the shrink list (ie not on the superblock LRU list).
 *
 * The per-cpu "nr_dentry_unused" counters are updated with
 * the DCACHE_LRU_LIST bit.
 *
 * These helper functions make sure we always follow the
 * rules. d_lock must be held by the caller.
 */
#define D_FLAG_VERIFY(dentry,x) WARN_ON_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRINK_LIST)) != (x))
static void d_lru_add(struct dentry *dentry)
{
        D_FLAG_VERIFY(dentry, 0);
        dentry->d_flags |= DCACHE_LRU_LIST;
        this_cpu_inc(nr_dentry_unused);
        WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
}

static void d_lru_del(struct dentry *dentry)
{
        D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
        dentry->d_flags &= ~DCACHE_LRU_LIST;
        this_cpu_dec(nr_dentry_unused);
        WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
}

static void d_shrink_del(struct dentry *dentry)
{
        D_FLAG_VERIFY(dentry, DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
        list_del_init(&dentry->d_lru);
        dentry->d_flags &= ~(DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
        this_cpu_dec(nr_dentry_unused);
}

static void d_shrink_add(struct dentry *dentry, struct list_head *list)
{
        D_FLAG_VERIFY(dentry, 0);
        list_add(&dentry->d_lru, list);
        dentry->d_flags |= DCACHE_SHRINK_LIST | DCACHE_LRU_LIST;
        this_cpu_inc(nr_dentry_unused);
}

/*
 * These can only be called under the global LRU lock, ie during the
 * callback for freeing the LRU list. "isolate" removes it from the
 * LRU lists entirely, while shrink_move moves it to the indicated
 * private list.
 */
static void d_lru_isolate(struct dentry *dentry)
{
        D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
        dentry->d_flags &= ~DCACHE_LRU_LIST;
        this_cpu_dec(nr_dentry_unused);
        list_del_init(&dentry->d_lru);
}

static void d_lru_shrink_move(struct dentry *dentry, struct list_head *list)
{
        D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
        dentry->d_flags |= DCACHE_SHRINK_LIST;
        list_move_tail(&dentry->d_lru, list);
}

/*
 * dentry_lru_(add|del)_list) must be called with d_lock held.
 */
static void dentry_lru_add(struct dentry *dentry)
{
        if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
                d_lru_add(dentry);
}

/*
 * Remove a dentry with references from the LRU.
 *
 * If we are on the shrink list, then we can get to try_prune_one_dentry() and
 * lose our last reference through the parent walk. In this case, we need to
 * remove ourselves from the shrink list, not the LRU.
 */
static void dentry_lru_del(struct dentry *dentry)
{
        if (dentry->d_flags & DCACHE_LRU_LIST) {
                if (dentry->d_flags & DCACHE_SHRINK_LIST)
                        return d_shrink_del(dentry);
                d_lru_del(dentry);
        }
}

/**
 * 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 d_walk() that we are no longer attached to the
         * dentry tree
         */
        dentry->d_flags |= DCACHE_DENTRY_KILLED;
        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;
}

/**
 * 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)) {
                struct hlist_bl_head *b;
                /*
                 * Hashed dentries are normally on the dentry hashtable,
                 * with the exception of those newly allocated by
                 * d_obtain_alias, which are always IS_ROOT:
                 */
                if (unlikely(IS_ROOT(dentry)))
                        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);
                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);

/*
 * 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 struct dentry *
dentry_kill(struct dentry *dentry, int unlock_on_failure)
        __releases(dentry->d_lock)
{
        struct inode *inode;
        struct dentry *parent;

        inode = dentry->d_inode;
        if (inode && !spin_trylock(&inode->i_lock)) {
relock:
                if (unlock_on_failure) {
                        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;
        }

        /*
         * The dentry is now unrecoverably dead to the world.
         */
        lockref_mark_dead(&dentry->d_lockref);

        /*
         * inform the fs via d_prune that this dentry is about to be
         * unhashed and destroyed.
         */
        if ((dentry->d_flags & DCACHE_OP_PRUNE) && !d_unhashed(dentry))
                dentry->d_op->d_prune(dentry);

        dentry_lru_del(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 (unlikely(!dentry))
                return;

repeat:
        if (lockref_put_or_lock(&dentry->d_lockref))
                return;

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

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

        if (!(dentry->d_flags & DCACHE_REFERENCED))
                dentry->d_flags |= DCACHE_REFERENCED;
        dentry_lru_add(dentry);

        dentry->d_lockref.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_lockref.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_lockref.count++;
}

static inline void __dget(struct dentry *dentry)
{
        lockref_get(&dentry->d_lockref);
}

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

        /*
         * Do optimistic parent lookup without any
         * locking.
         */
        rcu_read_lock();
        ret = ACCESS_ONCE(dentry->d_parent);
        gotref = lockref_get_not_zero(&ret->d_lockref);
        rcu_read_unlock();
        if (likely(gotref)) {
                if (likely(ret == ACCESS_ONCE(dentry->d_parent)))
                        return ret;
                dput(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_lockref.count);
        ret->d_lockref.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;
        hlist_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 (!hlist_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);
        hlist_for_each_entry(dentry, &inode->i_dentry, d_alias) {
                spin_lock(&dentry->d_lock);
                if (!dentry->d_lockref.count) {
                        /*
                         * inform the fs via d_prune that this dentry
                         * is about to be unhashed and destroyed.
                         */
                        if ((dentry->d_flags & DCACHE_OP_PRUNE) &&
                            !d_unhashed(dentry))
                                dentry->d_op->d_prune(dentry);

                        __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 struct dentry * 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 NULL;
        if (parent == dentry)
                return dentry;

        /* Prune ancestors. */
        dentry = parent;
        while (dentry) {
                if (lockref_put_or_lock(&dentry->d_lockref))
                        return NULL;
                dentry = dentry_kill(dentry, 1);
        }
        return NULL;
}

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 */

                /*
                 * Get the dentry lock, and re-verify that the dentry is
                 * this on the shrinking list. If it is, we know that
                 * DCACHE_SHRINK_LIST and DCACHE_LRU_LIST are set.
                 */
                spin_lock(&dentry->d_lock);
                if (dentry != list_entry(list->prev, struct dentry, d_lru)) {
                        spin_unlock(&dentry->d_lock);
                        continue;
                }

                /*
                 * The dispose list is isolated and dentries are not accounted
                 * to the LRU here, so we can simply remove it from the list
                 * here regardless of whether it is referenced or not.
                 */
                d_shrink_del(dentry);

                /*
                 * We found an inuse dentry which was not removed from
                 * the LRU because of laziness during lookup. Do not free it.
                 */
                if (dentry->d_lockref.count) {
                        spin_unlock(&dentry->d_lock);
                        continue;
                }
                rcu_read_unlock();

                /*
                 * If 'try_to_prune()' returns a dentry, it will
                 * be the same one we passed in, and d_lock will
                 * have been held the whole time, so it will not
                 * have been added to any other lists. We failed
                 * to get the inode lock.
                 *
                 * We just add it back to the shrink list.
                 */
                dentry = try_prune_one_dentry(dentry);

                rcu_read_lock();
                if (dentry) {
                        d_shrink_add(dentry, list);
                        spin_unlock(&dentry->d_lock);
                }
        }
        rcu_read_unlock();
}

static enum lru_status
dentry_lru_isolate(struct list_head *item, spinlock_t *lru_lock, void *arg)
{
        struct list_head *freeable = arg;
        struct dentry   *dentry = container_of(item, struct dentry, d_lru);


        /*
         * we are inverting the lru lock/dentry->d_lock here,
         * so use a trylock. If we fail to get the lock, just skip
         * it
         */
        if (!spin_trylock(&dentry->d_lock))
                return LRU_SKIP;

        /*
         * Referenced dentries are still in use. If they have active
         * counts, just remove them from the LRU. Otherwise give them
         * another pass through the LRU.
         */
        if (dentry->d_lockref.count) {
                d_lru_isolate(dentry);
                spin_unlock(&dentry->d_lock);
                return LRU_REMOVED;
        }

        if (dentry->d_flags & DCACHE_REFERENCED) {
                dentry->d_flags &= ~DCACHE_REFERENCED;
                spin_unlock(&dentry->d_lock);

                /*
                 * The list move itself will be made by the common LRU code. At
                 * this point, we've dropped the dentry->d_lock but keep the
                 * lru lock. This is safe to do, since every list movement is
                 * protected by the lru lock even if both locks are held.
                 *
                 * This is guaranteed by the fact that all LRU management
                 * functions are intermediated by the LRU API calls like
                 * list_lru_add and list_lru_del. List movement in this file
                 * only ever occur through this functions or through callbacks
                 * like this one, that are called from the LRU API.
                 *
                 * The only exceptions to this are functions like
                 * shrink_dentry_list, and code that first checks for the
                 * DCACHE_SHRINK_LIST flag.  Those are guaranteed to be
                 * operating only with stack provided lists after they are
                 * properly isolated from the main list.  It is thus, always a
                 * local access.
                 */
                return LRU_ROTATE;
        }

        d_lru_shrink_move(dentry, freeable);
        spin_unlock(&dentry->d_lock);

        return LRU_REMOVED;
}

/**
 * prune_dcache_sb - shrink the dcache
 * @sb: superblock
 * @nr_to_scan : number of entries to try to free
 * @nid: which node to scan for freeable entities
 *
 * 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.
 */
long prune_dcache_sb(struct super_block *sb, unsigned long nr_to_scan,
                     int nid)
{
        LIST_HEAD(dispose);
        long freed;

        freed = list_lru_walk_node(&sb->s_dentry_lru, nid, dentry_lru_isolate,
                                       &dispose, &nr_to_scan);
        shrink_dentry_list(&dispose);
        return freed;
}

static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
                                                spinlock_t *lru_lock, void *arg)
{
        struct list_head *freeable = arg;

        struct dentry   *dentry = container_of(item, struct dentry, d_lru);

        /*
         * we are inverting the lru lock/dentry->d_lock here,
         * so use a trylock. If we fail to get the lock, just skip
         * it
         */
        if (!spin_trylock(&dentry->d_lock))
                return LRU_SKIP;

        d_lru_shrink_move(dentry, freeable);
        spin_unlock(&dentry->d_lock);

        return LRU_REMOVED;
}


/**
 * 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)
{
        long freed;

        do {
                LIST_HEAD(dispose);

                freed = list_lru_walk(&sb->s_dentry_lru,
                        dentry_lru_isolate_shrink, &dispose, UINT_MAX);

                this_cpu_sub(nr_dentry_unused, freed);
                shrink_dentry_list(&dispose);
        } while (freed > 0);
}
EXPORT_SYMBOL(shrink_dcache_sb);

/**
 * enum d_walk_ret - action to talke during tree walk
 * @D_WALK_CONTINUE:    contrinue walk
 * @D_WALK_QUIT:        quit walk
 * @D_WALK_NORETRY:     quit when retry is needed
 * @D_WALK_SKIP:        skip this dentry and its children
 */
enum d_walk_ret {
        D_WALK_CONTINUE,
        D_WALK_QUIT,
        D_WALK_NORETRY,
        D_WALK_SKIP,
};

/**
 * d_walk - walk the dentry tree
 * @parent:     start of walk
 * @data:       data passed to @enter() and @finish()
 * @enter:      callback when first entering the dentry
 * @finish:     callback when successfully finished the walk
 *
 * The @enter() and @finish() callbacks are called with d_lock held.
 */
static void d_walk(struct dentry *parent, void *data,
                   enum d_walk_ret (*enter)(void *, struct dentry *),
                   void (*finish)(void *))
{
        struct dentry *this_parent;
        struct list_head *next;
        unsigned seq = 0;
        enum d_walk_ret ret;
        bool retry = true;

again:
        read_seqbegin_or_lock(&rename_lock, &seq);
        this_parent = parent;
        spin_lock(&this_parent->d_lock);

        ret = enter(data, this_parent);
        switch (ret) {
        case D_WALK_CONTINUE:
                break;
        case D_WALK_QUIT:
        case D_WALK_SKIP:
                goto out_unlock;
        case D_WALK_NORETRY:
                retry = false;
                break;
        }
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);

                ret = enter(data, dentry);
                switch (ret) {
                case D_WALK_CONTINUE:
                        break;
                case D_WALK_QUIT:
                        spin_unlock(&dentry->d_lock);
                        goto out_unlock;
                case D_WALK_NORETRY:
                        retry = false;
                        break;
                case D_WALK_SKIP:
                        spin_unlock(&dentry->d_lock);
                        continue;
                }

                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 = child->d_parent;

                rcu_read_lock();
                spin_unlock(&child->d_lock);
                spin_lock(&this_parent->d_lock);

                /*
                 * might go back up the wrong parent if we have had a rename
                 * or deletion
                 */
                if (this_parent != child->d_parent ||
                         (child->d_flags & DCACHE_DENTRY_KILLED) ||
                         need_seqretry(&rename_lock, seq)) {
                        spin_unlock(&this_parent->d_lock);
                        rcu_read_unlock();
                        goto rename_retry;
                }
                rcu_read_unlock();
                next = child->d_u.d_child.next;
                goto resume;
        }
        if (need_seqretry(&rename_lock, seq)) {
                spin_unlock(&this_parent->d_lock);
                goto rename_retry;
        }
        if (finish)
                finish(data);

out_unlock:
        spin_unlock(&this_parent->d_lock);
        done_seqretry(&rename_lock, seq);
        return;

rename_retry:
        if (!retry)
                return;
        seq = 1;
        goto again;
}

/*
 * 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.
 */

static enum d_walk_ret check_mount(void *data, struct dentry *dentry)
{
        int *ret = data;
        if (d_mountpoint(dentry)) {
                *ret = 1;
                return D_WALK_QUIT;
        }
        return D_WALK_CONTINUE;
}

/**
 * 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)
{
        int ret = 0;

        d_walk(parent, &ret, check_mount, NULL);

        return ret;
}
EXPORT_SYMBOL(have_submounts);

/*
 * Called by mount code to set a mountpoint and check if the mountpoint is
 * reachable (e.g. NFS can unhash a directory dentry and then the complete
 * subtree can become unreachable).
 *
 * Only one of check_submounts_and_drop() and d_set_mounted() must succeed.  For
 * this reason take rename_lock and d_lock on dentry and ancestors.
 */
int d_set_mounted(struct dentry *dentry)
{
        struct dentry *p;
        int ret = -ENOENT;
        write_seqlock(&rename_lock);
        for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
                /* Need exclusion wrt. check_submounts_and_drop() */
                spin_lock(&p->d_lock);
                if (unlikely(d_unhashed(p))) {
                        spin_unlock(&p->d_lock);
                        goto out;
                }
                spin_unlock(&p->d_lock);
        }
        spin_lock(&dentry->d_lock);
        if (!d_unlinked(dentry)) {
                dentry->d_flags |= DCACHE_MOUNTED;
                ret = 0;
        }
        spin_unlock(&dentry->d_lock);
out:
        write_sequnlock(&rename_lock);
        return ret;
}

/*
 * Search the dentry child list of 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.
 */

struct select_data {
        struct dentry *start;
        struct list_head dispose;
        int found;
};

static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
{
        struct select_data *data = _data;
        enum d_walk_ret ret = D_WALK_CONTINUE;

        if (data->start == dentry)
                goto out;

        /*
         * move only zero ref count dentries to the dispose list.
         *
         * Those which are presently on the shrink list, being processed
         * by shrink_dentry_list(), shouldn't be moved.  Otherwise the
         * loop in shrink_dcache_parent() might not make any progress
         * and loop forever.
         */
        if (dentry->d_lockref.count) {
                dentry_lru_del(dentry);
        } else if (!(dentry->d_flags & DCACHE_SHRINK_LIST)) {
                /*
                 * We can't use d_lru_shrink_move() because we
                 * need to get the global LRU lock and do the
                 * LRU accounting.
                 */
                d_lru_del(dentry);
                d_shrink_add(dentry, &data->dispose);
                data->found++;
                ret = D_WALK_NORETRY;
        }
        /*
         * 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 (data->found && need_resched())
                ret = D_WALK_QUIT;
out:
        return ret;
}

/**
 * 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)
{
        for (;;) {
                struct select_data data;

                INIT_LIST_HEAD(&data.dispose);
                data.start = parent;
                data.found = 0;

                d_walk(parent, &data, select_collect, NULL);
                if (!data.found)
                        break;

                shrink_dentry_list(&data.dispose);
                cond_resched();
        }
}
EXPORT_SYMBOL(shrink_dcache_parent);

static enum d_walk_ret umount_collect(void *_data, struct dentry *dentry)
{
        struct select_data *data = _data;
        enum d_walk_ret ret = D_WALK_CONTINUE;

        if (dentry->d_lockref.count) {
                dentry_lru_del(dentry);
                if (likely(!list_empty(&dentry->d_subdirs)))
                        goto out;
                if (dentry == data->start && dentry->d_lockref.count == 1)
                        goto out;
                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_lockref.count,
                       dentry->d_sb->s_type->name,
                       dentry->d_sb->s_id);
                BUG();
        } else if (!(dentry->d_flags & DCACHE_SHRINK_LIST)) {
                /*
                 * We can't use d_lru_shrink_move() because we
                 * need to get the global LRU lock and do the
                 * LRU accounting.
                 */
                if (dentry->d_flags & DCACHE_LRU_LIST)
                        d_lru_del(dentry);
                d_shrink_add(dentry, &data->dispose);
                data->found++;
                ret = D_WALK_NORETRY;
        }
out:
        if (data->found && need_resched())
                ret = D_WALK_QUIT;
        return ret;
}

/*
 * destroy the dentries attached to a superblock on unmounting
 */
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;
        for (;;) {
                struct select_data data;

                INIT_LIST_HEAD(&data.dispose);
                data.start = dentry;
                data.found = 0;

                d_walk(dentry, &data, umount_collect, NULL);
                if (!data.found)
                        break;

                shrink_dentry_list(&data.dispose);
                cond_resched();
        }
        d_drop(dentry);
        dput(dentry);

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

                INIT_LIST_HEAD(&data.dispose);
                data.start = NULL;
                data.found = 0;

                d_walk(dentry, &data, umount_collect, NULL);
                if (data.found)
                        shrink_dentry_list(&data.dispose);
                cond_resched();
        }
}

static enum d_walk_ret check_and_collect(void *_data, struct dentry *dentry)
{
        struct select_data *data = _data;

        if (d_mountpoint(dentry)) {
                data->found = -EBUSY;
                return D_WALK_QUIT;
        }

        return select_collect(_data, dentry);
}

static void check_and_drop(void *_data)
{
        struct select_data *data = _data;

        if (d_mountpoint(data->start))
                data->found = -EBUSY;
        if (!data->found)
                __d_drop(data->start);
}

/**
 * check_submounts_and_drop - prune dcache, check for submounts and drop
 *
 * All done as a single atomic operation relative to has_unlinked_ancestor().
 * Returns 0 if successfully unhashed @parent.  If there were submounts then
 * return -EBUSY.
 *
 * @dentry: dentry to prune and drop
 */
int check_submounts_and_drop(struct dentry *dentry)
{
        int ret = 0;

        /* Negative dentries can be dropped without further checks */
        if (!dentry->d_inode) {
                d_drop(dentry);
                goto out;
        }

        for (;;) {
                struct select_data data;

                INIT_LIST_HEAD(&data.dispose);
                data.start = dentry;
                data.found = 0;

                d_walk(dentry, &data, check_and_collect, check_and_drop);
                ret = data.found;

                if (!list_empty(&data.dispose))
                        shrink_dentry_list(&data.dispose);

                if (ret <= 0)
                        break;

                cond_resched();
        }

out:
        return ret;
}
EXPORT_SYMBOL(check_submounts_and_drop);

/**
 * __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;

        /*
         * We guarantee that the inline name is always NUL-terminated.
         * This way the memcpy() done by the name switching in rename
         * will still always have a NUL at the end, even if we might
         * be overwriting an internal NUL character
         */
        dentry->d_iname[DNAME_INLINE_LEN-1] = 0;
        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.len = name->len;
        dentry->d_name.hash = name->hash;
        memcpy(dname, name->name, name->len);
        dname[name->len] = 0;

        /* Make sure we always see the terminating NUL character */
        smp_wmb();
        dentry->d_name.name = dname;

        dentry->d_lockref.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_HLIST_NODE(&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);

/**
 * d_alloc_pseudo - allocate a dentry (for lookup-less filesystems)
 * @sb: the superblock
 * @name: qstr of the name
 *
 * For a filesystem that just pins its dentries in memory and never
 * performs lookups at all, return an unhashed IS_ROOT dentry.
 */
struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
{
        return __d_alloc(sb, name);
}
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_WEAK_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_weak_revalidate)
                dentry->d_flags |= DCACHE_OP_WEAK_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 unsigned d_flags_for_inode(struct inode *inode)
{
        unsigned add_flags = DCACHE_FILE_TYPE;

        if (!inode)
                return DCACHE_MISS_TYPE;

        if (S_ISDIR(inode->i_mode)) {
                add_flags = DCACHE_DIRECTORY_TYPE;
                if (unlikely(!(inode->i_opflags & IOP_LOOKUP))) {
                        if (unlikely(!inode->i_op->lookup))
                                add_flags = DCACHE_AUTODIR_TYPE;
                        else
                                inode->i_opflags |= IOP_LOOKUP;
                }
        } else if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) {
                if (unlikely(inode->i_op->follow_link))
                        add_flags = DCACHE_SYMLINK_TYPE;
                else
                        inode->i_opflags |= IOP_NOFOLLOW;
        }

        if (unlikely(IS_AUTOMOUNT(inode)))
                add_flags |= DCACHE_NEED_AUTOMOUNT;
        return add_flags;
}

static void __d_instantiate(struct dentry *dentry, struct inode *inode)
{
        unsigned add_flags = d_flags_for_inode(inode);

        spin_lock(&dentry->d_lock);
        dentry->d_flags &= ~DCACHE_ENTRY_TYPE;
        dentry->d_flags |= add_flags;
        if (inode)
                hlist_add_head(&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(!hlist_unhashed(&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;
        }

        hlist_for_each_entry(alias, &inode->i_dentry, d_alias) {
                /*
                 * 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 (alias->d_name.hash != hash)
                        continue;
                if (alias->d_parent != entry->d_parent)
                        continue;
                if (alias->d_name.len != len)
                        continue;
                if (dentry_cmp(alias, 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(!hlist_unhashed(&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_instantiate_no_diralias - instantiate a non-aliased dentry
 * @entry: dentry to complete
 * @inode: inode to attach to this dentry
 *
 * Fill in inode information in the entry.  If a directory alias is found, then
 * return an error (and drop inode).  Together with d_materialise_unique() this
 * guarantees that a directory inode may never have more than one alias.
 */
int d_instantiate_no_diralias(struct dentry *entry, struct inode *inode)
{
        BUG_ON(!hlist_unhashed(&entry->d_alias));

        spin_lock(&inode->i_lock);
        if (S_ISDIR(inode->i_mode) && !hlist_empty(&inode->i_dentry)) {
                spin_unlock(&inode->i_lock);
                iput(inode);
                return -EBUSY;
        }
        __d_instantiate(entry, inode);
        spin_unlock(&inode->i_lock);
        security_d_instantiate(entry, inode);

        return 0;
}
EXPORT_SYMBOL(d_instantiate_no_diralias);

struct dentry *d_make_root(struct inode *root_inode)
{
        struct dentry *res = NULL;

        if (root_inode) {
                static const struct qstr name = QSTR_INIT("/", 1);

                res = __d_alloc(root_inode->i_sb, &name);
                if (res)
                        d_instantiate(res, root_inode);
                else
                        iput(root_inode);
        }
        return res;
}
EXPORT_SYMBOL(d_make_root);

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

        if (hlist_empty(&inode->i_dentry))
                return NULL;
        alias = hlist_entry(inode->i_dentry.first, struct dentry, d_alias);
        __dget(alias);
        return alias;
}

/**
 * d_find_any_alias - find any alias for a given inode
 * @inode: inode to find an alias for
 *
 * If any aliases exist for the given inode, take and return a
 * reference for one of them.  If no aliases exist, return %NULL.
 */
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;
}
EXPORT_SYMBOL(d_find_any_alias);

/**
 * 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 = QSTR_INIT("/", 1);
        struct dentry *tmp;
        struct dentry *res;
        unsigned add_flags;

        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 */
        add_flags = d_flags_for_inode(inode) | DCACHE_DISCONNECTED;

        spin_lock(&tmp->d_lock);
        tmp->d_inode = inode;
        tmp->d_flags |= add_flags;
        hlist_add_head(&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.
 *
 * Cluster filesystems may call this function with a negative, hashed dentry.
 * In that case, we know that the inode will be a regular file, and also this
 * will only occur during atomic_open. So we need to check for the dentry
 * being already hashed only in the final case.
 */
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_instantiate(dentry, inode);
                if (d_unhashed(dentry))
                        d_rehash(dentry);
        }
        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)
{
        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 (unlikely(IS_ERR(found)))
                goto err_out;
        if (!found) {
                new = d_alloc(dentry->d_parent, name);
                if (!new) {
                        found = ERR_PTR(-ENOMEM);
                        goto err_out;
                }

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