dcache.c

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/*
 * 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 "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)
 * 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(const struct dentry *parent,
                    unsigned int hash)
{
    hash += (unsigned long) parent / L1_CACHE_BYTES;
    hash = hash + (hash >> 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

/*
 * 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 = ~(~0ul << tcount*8);
    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(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);
}

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;
    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);
}

/*
 * 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_flags &= ~DCACHE_SHRINK_LIST;
    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_list(struct dentry *dentry, struct list_head *list)
{
    spin_lock(&dcache_lru_lock);
    if (list_empty(&dentry->d_lru)) {
        list_add_tail(&dentry->d_lru, list);
        dentry->d_sb->s_nr_dentry_unused++;
        dentry_stat.nr_unused++;
    } else {
        list_move_tail(&dentry->d_lru, list);
    }
    spin_unlock(&dcache_lru_lock);
}

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_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;
}

/*
 * 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);
    }
}

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);

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);

static struct dentry *__d_find_alias(struct inode *inode, int want_discon)
{
    struct dentry *alias, *discon_alias;
    struct hlist_node *p;

again:
    discon_alias = NULL;
    hlist_for_each_entry(alias, p, &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;
    struct hlist_node *p;
restart:
    spin_lock(&inode->i_lock);
    hlist_for_each_entry(dentry, p, &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();
}

void prune_dcache_sb(struct super_block *sb, int count)
{
    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 (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);
            dentry->d_flags |= DCACHE_SHRINK_LIST;
            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);
}

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;
                hlist_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_DENTRY_KILLED) ||
         (!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.
 */
 
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:
    if (locked)
        goto again;
    locked = 1;
    write_seqlock(&rename_lock);
    goto again;
}
EXPORT_SYMBOL(have_submounts);

/*
 * 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.
 */
static int select_parent(struct dentry *parent, struct list_head *dispose)
{
    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 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_count) {
            dentry_lru_del(dentry);
        } else if (!(dentry->d_flags & DCACHE_SHRINK_LIST)) {
            dentry_lru_move_list(dentry, dispose);
            dentry->d_flags |= DCACHE_SHRINK_LIST;
            found++;
        }
        /*
         * We can return to the caller if we have found some (this
         * ensures forward progress). We'll be coming back to find
         * the rest.
         */
        if (found && need_resched()) {
            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;
    if (locked)
        goto again;
    locked = 1;
    write_seqlock(&rename_lock);
    goto again;
}

void shrink_dcache_parent(struct dentry * parent)
{
    LIST_HEAD(dispose);
    int found;

    while ((found = select_parent(parent, &dispose)) != 0)
        shrink_dentry_list(&dispose);
}
EXPORT_SYMBOL(shrink_dcache_parent);

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_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;
}

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;
        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);
}

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);

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;
    struct hlist_node *p;

    if (!inode) {
        __d_instantiate(entry, NULL);
        return NULL;
    }

    hlist_for_each_entry(alias, p, &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);

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;
}

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);

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;
    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);

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);

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);

/*
 * Do the slow-case of the dentry name compare.
 *
 * Unlike the dentry_cmp() function, we need to atomically
 * load the name, length and inode information, so that the
 * filesystem can rely on them, and can use the 'name' and
 * 'len' information without worrying about walking off the
 * end of memory etc.
 *
 * Thus the read_seqcount_retry() and the "duplicate" info
 * in arguments (the low-level filesystem should not look
 * at the dentry inode or name contents directly, since
 * rename can change them while we're in RCU mode).
 */
enum slow_d_compare {
    D_COMP_OK,
    D_COMP_NOMATCH,
    D_COMP_SEQRETRY,
};

static noinline enum slow_d_compare slow_dentry_cmp(
        const struct dentry *parent,
        struct inode *inode,
        struct dentry *dentry,
        unsigned int seq,
        const struct qstr *name)
{
    int tlen = dentry->d_name.len;
    const char *tname = dentry->d_name.name;
    struct inode *i = dentry->d_inode;

    if (read_seqcount_retry(&dentry->d_seq, seq)) {
        cpu_relax();
        return D_COMP_SEQRETRY;
    }
    if (parent->d_op->d_compare(parent, inode,
                dentry, i,
                tlen, tname, name))
        return D_COMP_NOMATCH;
    return D_COMP_OK;
}

struct dentry *__d_lookup_rcu(const struct dentry *parent,
                const struct qstr *name,
                unsigned *seqp, struct inode *inode)
{
    u64 hashlen = name->hash_len;
    const unsigned char *str = name->name;
    struct hlist_bl_head *b = d_hash(parent, hashlen_hash(hashlen));
    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) {
        unsigned seq;

seqretry:
        /*
         * The dentry sequence count protects us from concurrent
         * renames, and thus protects inode, parent and name fields.
         *
         * The caller must perform a seqcount check in order
         * to do anything useful with the returned dentry,
         * including using the 'd_inode' pointer.
         *
         * NOTE! We do a "raw" seqcount_begin here. That means that
         * we don't wait for the sequence count to stabilize if it
         * is in the middle of a sequence change. If we do the slow
         * dentry compare, we will do seqretries until it is stable,
         * and if we end up with a successful lookup, we actually
         * want to exit RCU lookup anyway.
         */
        seq = raw_seqcount_begin(&dentry->d_seq);
        if (dentry->d_parent != parent)
            continue;
        if (d_unhashed(dentry))
            continue;
        *seqp = seq;

        if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
            if (dentry->d_name.hash != hashlen_hash(hashlen))
                continue;
            switch (slow_dentry_cmp(parent, inode, dentry, seq, name)) {
            case D_COMP_OK:
                return dentry;
            case D_COMP_NOMATCH:
                continue;
            default:
                goto seqretry;
            }
        }

        if (dentry->d_name.hash_len != hashlen)
            continue;
        if (!dentry_cmp(dentry, str, hashlen_len(hashlen)))
            return dentry;
    }
    return NULL;
}

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);

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) {

        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).
         */
        if (parent->d_flags & DCACHE_OP_COMPARE) {
            int tlen = dentry->d_name.len;
            const char *tname = dentry->d_name.name;
            if (parent->d_op->d_compare(parent, parent->d_inode,
                        dentry, dentry->d_inode,
                        tlen, tname, name))
                goto next;
        } else {
            if (dentry->d_name.len != len)
                goto next;
            if (dentry_cmp(dentry, 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;
}

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;
}

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
 */
 
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 (!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;
    }

    if (!d_unhashed(dentry))
        __d_drop(dentry);

    spin_unlock(&dentry->d_lock);

    fsnotify_nameremove(dentry, isdir);
}
EXPORT_SYMBOL(d_delete);

static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b)
{
    BUG_ON(!d_unhashed(entry));
    hlist_bl_lock(b);
    entry->d_flags |= DCACHE_RCUACCESS;
    hlist_bl_add_head_rcu(&entry->d_hash, b);
    hlist_bl_unlock(b);
}

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

void d_rehash(struct dentry * entry)
{
    spin_lock(&entry->d_lock);
    _d_rehash(entry);
    spin_unlock(&entry->d_lock);
}
EXPORT_SYMBOL(d_rehash);

void dentry_update_name_case(struct dentry *dentry, struct qstr *name)
{
    BUG_ON(!mutex_is_locked(&dentry->d_parent->d_inode->i_mutex));
    BUG_ON(dentry->d_name.len != name->len); /* d_lookup gives this */

    spin_lock(&dentry->d_lock);
    write_seqcount_begin(&dentry->d_seq);
    memcpy((unsigned char *)dentry->d_name.name, name->name, name->len);
    write_seqcount_end(&dentry->d_seq);
    spin_unlock(&dentry->d_lock);
}
EXPORT_SYMBOL(dentry_update_name_case);

static void switch_names(struct dentry *dentry, struct dentry *target)
{
    if (dname_external(target)) {
        if (dname_external(dentry)) {
            /*
             * Both external: swap the pointers
             */
            swap(target->d_name.name, dentry->d_name.name);
        } else {
            /*
             * dentry:internal, target:external.  Steal target's
             * storage and make target internal.
             */
            memcpy(target->d_iname, dentry->d_name.name,
                    dentry->d_name.len + 1);
            dentry->d_name.name = target->d_name.name;
            target->d_name.name = target->d_iname;
        }
    } else {
        if (dname_external(dentry)) {
            /*
             * dentry:external, target:internal.  Give dentry's
             * storage to target and make dentry internal
             */
            memcpy(dentry->d_iname, target->d_name.name,
                    target->d_name.len + 1);
            target->d_name.name = dentry->d_name.name;
            dentry->d_name.name = dentry->d_iname;
        } else {
            /*
             * Both are internal.  Just copy target to dentry
             */
            memcpy(dentry->d_iname, target->d_name.name,
                    target->d_name.len + 1);
            dentry->d_name.len = target->d_name.len;
            return;
        }
    }
    swap(dentry->d_name.len, target->d_name.len);
}

static void dentry_lock_for_move(struct dentry *dentry, struct dentry *target)
{
    /*
     * XXXX: do we really need to take target->d_lock?
     */
    if (IS_ROOT(dentry) || dentry->d_parent == target->d_parent)
        spin_lock(&target->d_parent->d_lock);
    else {
        if (d_ancestor(dentry->d_parent, target->d_parent)) {
            spin_lock(&dentry->d_parent->d_lock);
            spin_lock_nested(&target->d_parent->d_lock,
                        DENTRY_D_LOCK_NESTED);
        } else {
            spin_lock(&target->d_parent->d_lock);
            spin_lock_nested(&dentry->d_parent->d_lock,
                        DENTRY_D_LOCK_NESTED);
        }
    }
    if (target < dentry) {
        spin_lock_nested(&target->d_lock, 2);
        spin_lock_nested(&dentry->d_lock, 3);
    } else {
        spin_lock_nested(&dentry->d_lock, 2);
        spin_lock_nested(&target->d_lock, 3);
    }
}

static void dentry_unlock_parents_for_move(struct dentry *dentry,
                    struct dentry *target)
{
    if (target->d_parent != dentry->d_parent)
        spin_unlock(&dentry->d_parent->d_lock);
    if (target->d_parent != target)
        spin_unlock(&target->d_parent->d_lock);
}

/*
 * When switching names, the actual string doesn't strictly have to
 * be preserved in the target - because we're dropping the target
 * anyway. As such, we can just do a simple memcpy() to copy over
 * the new name before we switch.
 *
 * Note that we have to be a lot more careful about getting the hash
 * switched - we have to switch the hash value properly even if it
 * then no longer matches the actual (corrupted) string of the target.
 * The hash value has to match the hash queue that the dentry is on..
 */
/*
 * __d_move - move a dentry
 * @dentry: entry to move
 * @target: new dentry
 *
 * Update the dcache to reflect the move of a file name. Negative
 * dcache entries should not be moved in this way. Caller must hold
 * rename_lock, the i_mutex of the source and target directories,
 * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
 */
static void __d_move(struct dentry * dentry, struct dentry * target)
{
    if (!dentry->d_inode)
        printk(KERN_WARNING "VFS: moving negative dcache entry\n");

    BUG_ON(d_ancestor(dentry, target));
    BUG_ON(d_ancestor(target, dentry));

    dentry_lock_for_move(dentry, target);

    write_seqcount_begin(&dentry->d_seq);
    write_seqcount_begin(&target->d_seq);

    /* __d_drop does write_seqcount_barrier, but they're OK to nest. */

    /*
     * Move the dentry to the target hash queue. Don't bother checking
     * for the same hash queue because of how unlikely it is.
     */
    __d_drop(dentry);
    __d_rehash(dentry, d_hash(target->d_parent, target->d_name.hash));

    /* Unhash the target: dput() will then get rid of it */
    __d_drop(target);

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

    /* Switch the names.. */
    switch_names(dentry, target);
    swap(dentry->d_name.hash, target->d_name.hash);

    /* ... and switch the parents */
    if (IS_ROOT(dentry)) {
        dentry->d_parent = target->d_parent;
        target->d_parent = target;
        INIT_LIST_HEAD(&target->d_u.d_child);
    } else {
        swap(dentry->d_parent, target->d_parent);

        /* And add them back to the (new) parent lists */
        list_add(&target->d_u.d_child, &target->d_parent->d_subdirs);
    }

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

    write_seqcount_end(&target->d_seq);
    write_seqcount_end(&dentry->d_seq);

    dentry_unlock_parents_for_move(dentry, target);
    spin_unlock(&target->d_lock);
    fsnotify_d_move(dentry);
    spin_unlock(&dentry->d_lock);
}

/*
 * d_move - move a dentry
 * @dentry: entry to move
 * @target: new dentry
 *
 * Update the dcache to reflect the move of a file name. Negative
 * dcache entries should not be moved in this way. See the locking
 * requirements for __d_move.
 */
void d_move(struct dentry *dentry, struct dentry *target)
{
    write_seqlock(&rename_lock);
    __d_move(dentry, target);
    write_sequnlock(&rename_lock);
}
EXPORT_SYMBOL(d_move);

struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
{
    struct dentry *p;

    for (p = p2; !IS_ROOT(p); p = p->d_parent) {
        if (p->d_parent == p1)
            return p;
    }
    return NULL;
}

/*
 * This helper attempts to cope with remotely renamed directories
 *
 * It assumes that the caller is already holding
 * dentry->d_parent->d_inode->i_mutex, inode->i_lock and rename_lock
 *
 * Note: If ever the locking in lock_rename() changes, then please
 * remember to update this too...
 */
static struct dentry *__d_unalias(struct inode *inode,
        struct dentry *dentry, struct dentry *alias)
{
    struct mutex *m1 = NULL, *m2 = NULL;
    struct dentry *ret = ERR_PTR(-EBUSY);

    /* If alias and dentry share a parent, then no extra locks required */
    if (alias->d_parent == dentry->d_parent)
        goto out_unalias;

    /* See lock_rename() */
    if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
        goto out_err;
    m1 = &dentry->d_sb->s_vfs_rename_mutex;
    if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex))
        goto out_err;
    m2 = &alias->d_parent->d_inode->i_mutex;
out_unalias:
    if (likely(!d_mountpoint(alias))) {
        __d_move(alias, dentry);
        ret = alias;
    }
out_err:
    spin_unlock(&inode->i_lock);
    if (m2)
        mutex_unlock(m2);
    if (m1)
        mutex_unlock(m1);
    return ret;
}

/*
 * Prepare an anonymous dentry for life in the superblock's dentry tree as a
 * named dentry in place of the dentry to be replaced.
 * returns with anon->d_lock held!
 */
static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
{
    struct dentry *dparent, *aparent;

    dentry_lock_for_move(anon, dentry);

    write_seqcount_begin(&dentry->d_seq);
    write_seqcount_begin(&anon->d_seq);

    dparent = dentry->d_parent;
    aparent = anon->d_parent;

    switch_names(dentry, anon);
    swap(dentry->d_name.hash, anon->d_name.hash);

    dentry->d_parent = (aparent == anon) ? dentry : aparent;
    list_del(&dentry->d_u.d_child);
    if (!IS_ROOT(dentry))
        list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
    else
        INIT_LIST_HEAD(&dentry->d_u.d_child);

    anon->d_parent = (dparent == dentry) ? anon : dparent;
    list_del(&anon->d_u.d_child);
    if (!IS_ROOT(anon))
        list_add(&anon->d_u.d_child, &anon->d_parent->d_subdirs);
    else
        INIT_LIST_HEAD(&anon->d_u.d_child);

    write_seqcount_end(&dentry->d_seq);
    write_seqcount_end(&anon->d_seq);

    dentry_unlock_parents_for_move(anon, dentry);
    spin_unlock(&dentry->d_lock);

    /* anon->d_lock still locked, returns locked */
    anon->d_flags &= ~DCACHE_DISCONNECTED;
}

struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
{
    struct dentry *actual;

    BUG_ON(!d_unhashed(dentry));

    if (!inode) {
        actual = dentry;
        __d_instantiate(dentry, NULL);
        d_rehash(actual);
        goto out_nolock;
    }

    spin_lock(&inode->i_lock);

    if (S_ISDIR(inode->i_mode)) {
        struct dentry *alias;

        /* Does an aliased dentry already exist? */
        alias = __d_find_alias(inode, 0);
        if (alias) {
            actual = alias;
            write_seqlock(&rename_lock);

            if (d_ancestor(alias, dentry)) {
                /* Check for loops */
                actual = ERR_PTR(-ELOOP);
                spin_unlock(&inode->i_lock);
            } else if (IS_ROOT(alias)) {
                /* Is this an anonymous mountpoint that we
                 * could splice into our tree? */
                __d_materialise_dentry(dentry, alias);
                write_sequnlock(&rename_lock);
                __d_drop(alias);
                goto found;
            } else {
                /* Nope, but we must(!) avoid directory
                 * aliasing. This drops inode->i_lock */
                actual = __d_unalias(inode, dentry, alias);
            }
            write_sequnlock(&rename_lock);
            if (IS_ERR(actual)) {
                if (PTR_ERR(actual) == -ELOOP)
                    pr_warn_ratelimited(
                        "VFS: Lookup of '%s' in %s %s"
                        " would have caused loop\n",
                        dentry->d_name.name,
                        inode->i_sb->s_type->name,
                        inode->i_sb->s_id);
                dput(alias);
            }
            goto out_nolock;
        }
    }

    /* Add a unique reference */
    actual = __d_instantiate_unique(dentry, inode);
    if (!actual)
        actual = dentry;
    else
        BUG_ON(!d_unhashed(actual));

    spin_lock(&actual->d_lock);
found:
    _d_rehash(actual);
    spin_unlock(&actual->d_lock);
    spin_unlock(&inode->i_lock);
out_nolock:
    if (actual == dentry) {
        security_d_instantiate(dentry, inode);
        return NULL;
    }

    iput(inode);
    return actual;
}
EXPORT_SYMBOL_GPL(d_materialise_unique);

static int prepend(char **buffer, int *buflen, const char *str, int namelen)
{
    *buflen -= namelen;
    if (*buflen < 0)
        return -ENAMETOOLONG;
    *buffer -= namelen;
    memcpy(*buffer, str, namelen);
    return 0;
}

static int prepend_name(char **buffer, int *buflen, struct qstr *name)
{
    return prepend(buffer, buflen, name->name, name->len);
}

static int prepend_path(const struct path *path,
            const struct path *root,
            char **buffer, int *buflen)
{
    struct dentry *dentry = path->dentry;
    struct vfsmount *vfsmnt = path->mnt;
    struct mount *mnt = real_mount(vfsmnt);
    bool slash = false;
    int error = 0;

    br_read_lock(&vfsmount_lock);
    while (dentry != root->dentry || vfsmnt != root->mnt) {
        struct dentry * parent;

        if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
            /* Global root? */
            if (!mnt_has_parent(mnt))
                goto global_root;
            dentry = mnt->mnt_mountpoint;
            mnt = mnt->mnt_parent;
            vfsmnt = &mnt->mnt;
            continue;
        }
        parent = dentry->d_parent;
        prefetch(parent);
        spin_lock(&dentry->d_lock);
        error = prepend_name(buffer, buflen, &dentry->d_name);
        spin_unlock(&dentry->d_lock);
        if (!error)
            error = prepend(buffer, buflen, "/", 1);
        if (error)
            break;

        slash = true;
        dentry = parent;
    }

    if (!error && !slash)
        error = prepend(buffer, buflen, "/", 1);

out:
    br_read_unlock(&vfsmount_lock);
    return error;

global_root:
    /*
     * Filesystems needing to implement special "root names"
     * should do so with ->d_dname()
     */
    if (IS_ROOT(dentry) &&
        (dentry->d_name.len != 1 || dentry->d_name.name[0] != '/')) {
        WARN(1, "Root dentry has weird name <%.*s>\n",
             (int) dentry->d_name.len, dentry->d_name.name);
    }
    if (!slash)
        error = prepend(buffer, buflen, "/", 1);
    if (!error)
        error = is_mounted(vfsmnt) ? 1 : 2;
    goto out;
}

char *__d_path(const struct path *path,
           const struct path *root,
           char *buf, int buflen)
{
    char *res = buf + buflen;
    int error;

    prepend(&res, &buflen, "\0", 1);
    write_seqlock(&rename_lock);
    error = prepend_path(path, root, &res, &buflen);
    write_sequnlock(&rename_lock);

    if (error < 0)
        return ERR_PTR(error);
    if (error > 0)
        return NULL;
    return res;
}

char *d_absolute_path(const struct path *path,
           char *buf, int buflen)
{
    struct path root = {};
    char *res = buf + buflen;
    int error;

    prepend(&res, &buflen, "\0", 1);
    write_seqlock(&rename_lock);
    error = prepend_path(path, &root, &res, &buflen);
    write_sequnlock(&rename_lock);

    if (error > 1)
        error = -EINVAL;
    if (error < 0)
        return ERR_PTR(error);
    return res;
}

/*
 * same as __d_path but appends "(deleted)" for unlinked files.
 */
static int path_with_deleted(const struct path *path,
                 const struct path *root,
                 char **buf, int *buflen)
{
    prepend(buf, buflen, "\0", 1);
    if (d_unlinked(path->dentry)) {
        int error = prepend(buf, buflen, " (deleted)", 10);
        if (error)
            return error;
    }

    return prepend_path(path, root, buf, buflen);
}

static int prepend_unreachable(char **buffer, int *buflen)
{
    return prepend(buffer, buflen, "(unreachable)", 13);
}

char *d_path(const struct path *path, char *buf, int buflen)
{
    char *res = buf + buflen;
    struct path root;
    int error;

    /*
     * We have various synthetic filesystems that never get mounted.  On
     * these filesystems dentries are never used for lookup purposes, and
     * thus don't need to be hashed.  They also don't need a name until a
     * user wants to identify the object in /proc/pid/fd/.  The little hack
     * below allows us to generate a name for these objects on demand:
     */
    if (path->dentry->d_op && path->dentry->d_op->d_dname)
        return path->dentry->d_op->d_dname(path->dentry, buf, buflen);

    get_fs_root(current->fs, &root);
    write_seqlock(&rename_lock);
    error = path_with_deleted(path, &root, &res, &buflen);
    if (error < 0)
        res = ERR_PTR(error);
    write_sequnlock(&rename_lock);
    path_put(&root);
    return res;
}
EXPORT_SYMBOL(d_path);

char *d_path_with_unreachable(const struct path *path, char *buf, int buflen)
{
    char *res = buf + buflen;
    struct path root;
    int error;

    if (path->dentry->d_op && path->dentry->d_op->d_dname)
        return path->dentry->d_op->d_dname(path->dentry, buf, buflen);

    get_fs_root(current->fs, &root);
    write_seqlock(&rename_lock);
    error = path_with_deleted(path, &root, &res, &buflen);
    if (error > 0)
        error = prepend_unreachable(&res, &buflen);
    write_sequnlock(&rename_lock);
    path_put(&root);
    if (error)
        res =  ERR_PTR(error);

    return res;
}

/*
 * Helper function for dentry_operations.d_dname() members
 */
char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
            const char *fmt, ...)
{
    va_list args;
    char temp[64];
    int sz;

    va_start(args, fmt);
    sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
    va_end(args);

    if (sz > sizeof(temp) || sz > buflen)
        return ERR_PTR(-ENAMETOOLONG);

    buffer += buflen - sz;
    return memcpy(buffer, temp, sz);
}

/*
 * Write full pathname from the root of the filesystem into the buffer.
 */
static char *__dentry_path(struct dentry *dentry, char *buf, int buflen)
{
    char *end = buf + buflen;
    char *retval;

    prepend(&end, &buflen, "\0", 1);
    if (buflen < 1)
        goto Elong;
    /* Get '/' right */
    retval = end-1;
    *retval = '/';

    while (!IS_ROOT(dentry)) {
        struct dentry *parent = dentry->d_parent;
        int error;

        prefetch(parent);
        spin_lock(&dentry->d_lock);
        error = prepend_name(&end, &buflen, &dentry->d_name);
        spin_unlock(&dentry->d_lock);
        if (error != 0 || prepend(&end, &buflen, "/", 1) != 0)
            goto Elong;

        retval = end;
        dentry = parent;
    }
    return retval;
Elong:
    return ERR_PTR(-ENAMETOOLONG);
}

char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
{
    char *retval;

    write_seqlock(&rename_lock);
    retval = __dentry_path(dentry, buf, buflen);
    write_sequnlock(&rename_lock);

    return retval;
}
EXPORT_SYMBOL(dentry_path_raw);

char *dentry_path(struct dentry *dentry, char *buf, int buflen)
{
    char *p = NULL;
    char *retval;

    write_seqlock(&rename_lock);
    if (d_unlinked(dentry)) {
        p = buf + buflen;
        if (prepend(&p, &buflen, "//deleted", 10) != 0)
            goto Elong;
        buflen++;
    }
    retval = __dentry_path(dentry, buf, buflen);
    write_sequnlock(&rename_lock);
    if (!IS_ERR(retval) && p)
        *p = '/';   /* restore '/' overriden with '\0' */
    return retval;
Elong:
    return ERR_PTR(-ENAMETOOLONG);
}

/*
 * NOTE! The user-level library version returns a
 * character pointer. The kernel system call just
 * returns the length of the buffer filled (which
 * includes the ending '\0' character), or a negative
 * error value. So libc would do something like
 *
 *  char *getcwd(char * buf, size_t size)
 *  {
 *      int retval;
 *
 *      retval = sys_getcwd(buf, size);
 *      if (retval >= 0)
 *          return buf;
 *      errno = -retval;
 *      return NULL;
 *  }
 */
SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
{
    int error;
    struct path pwd, root;
    char *page = (char *) __get_free_page(GFP_USER);

    if (!page)
        return -ENOMEM;

    get_fs_root_and_pwd(current->fs, &root, &pwd);

    error = -ENOENT;
    write_seqlock(&rename_lock);
    if (!d_unlinked(pwd.dentry)) {
        unsigned long len;
        char *cwd = page + PAGE_SIZE;
        int buflen = PAGE_SIZE;

        prepend(&cwd, &buflen, "\0", 1);
        error = prepend_path(&pwd, &root, &cwd, &buflen);
        write_sequnlock(&rename_lock);

        if (error < 0)
            goto out;

        /* Unreachable from current root */
        if (error > 0) {
            error = prepend_unreachable(&cwd, &buflen);
            if (error)
                goto out;
        }

        error = -ERANGE;
        len = PAGE_SIZE + page - cwd;
        if (len <= size) {
            error = len;
            if (copy_to_user(buf, cwd, len))
                error = -EFAULT;
        }
    } else {
        write_sequnlock(&rename_lock);
    }

out:
    path_put(&pwd);
    path_put(&root);
    free_page((unsigned long) page);
    return error;
}

/*
 * Test whether new_dentry is a subdirectory of old_dentry.
 *
 * Trivially implemented using the dcache structure
 */

int is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
{
    int result;
    unsigned seq;

    if (new_dentry == old_dentry)
        return 1;

    do {
        /* for restarting inner loop in case of seq retry */
        seq = read_seqbegin(&rename_lock);
        /*
         * Need rcu_readlock to protect against the d_parent trashing
         * due to d_move
         */
        rcu_read_lock();
        if (d_ancestor(old_dentry, new_dentry))
            result = 1;
        else
            result = 0;
        rcu_read_unlock();
    } while (read_seqretry(&rename_lock, seq));

    return result;
}

void d_genocide(struct dentry *root)
{
    struct dentry *this_parent;
    struct list_head *next;
    unsigned seq;
    int locked = 0;

    seq = read_seqbegin(&rename_lock);
again:
    this_parent = root;
    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);
        if (d_unhashed(dentry) || !dentry->d_inode) {
            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;
        }
        if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
            dentry->d_flags |= DCACHE_GENOCIDE;
            dentry->d_count--;
        }
        spin_unlock(&dentry->d_lock);
    }
    if (this_parent != root) {
        struct dentry *child = this_parent;
        if (!(this_parent->d_flags & DCACHE_GENOCIDE)) {
            this_parent->d_flags |= DCACHE_GENOCIDE;
            this_parent->d_count--;
        }
        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;

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

ino_t find_inode_number(struct dentry *dir, struct qstr *name)
{
    struct dentry * dentry;
    ino_t ino = 0;

    dentry = d_hash_and_lookup(dir, name);
    if (dentry) {
        if (dentry->d_inode)
            ino = dentry->d_inode->i_ino;
        dput(dentry);
    }
    return ino;
}
EXPORT_SYMBOL(find_inode_number);

static __initdata unsigned long dhash_entries;
static int __init set_dhash_entries(char *str)
{
    if (!str)
        return 0;
    dhash_entries = simple_strtoul(str, &str, 0);
    return 1;
}
__setup("dhash_entries=", set_dhash_entries);

static void __init dcache_init_early(void)
{
    unsigned int loop;

    /* If hashes are distributed across NUMA nodes, defer
     * hash allocation until vmalloc space is available.
     */
    if (hashdist)
        return;

    dentry_hashtable =
        alloc_large_system_hash("Dentry cache",
                    sizeof(struct hlist_bl_head),
                    dhash_entries,
                    13,
                    HASH_EARLY,
                    &d_hash_shift,
                    &d_hash_mask,
                    0,
                    0);

    for (loop = 0; loop < (1U << d_hash_shift); loop++)
        INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
}

static void __init dcache_init(void)
{
    unsigned int loop;

    /* 
     * A constructor could be added for stable state like the lists,
     * but it is probably not worth it because of the cache nature
     * of the dcache. 
     */
    dentry_cache = KMEM_CACHE(dentry,
        SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);

    /* Hash may have been set up in dcache_init_early */
    if (!hashdist)
        return;

    dentry_hashtable =
        alloc_large_system_hash("Dentry cache",
                    sizeof(struct hlist_bl_head),
                    dhash_entries,
                    13,
                    0,
                    &d_hash_shift,
                    &d_hash_mask,
                    0,
                    0);

    for (loop = 0; loop < (1U << d_hash_shift); loop++)
        INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
}

/* SLAB cache for __getname() consumers */
struct kmem_cache *names_cachep __read_mostly;
EXPORT_SYMBOL(names_cachep);

EXPORT_SYMBOL(d_genocide);

void __init vfs_caches_init_early(void)
{
    dcache_init_early();
    inode_init_early();
}

void __init vfs_caches_init(unsigned long mempages)
{
    unsigned long reserve;

    /* Base hash sizes on available memory, with a reserve equal to
           150% of current kernel size */

    reserve = min((mempages - nr_free_pages()) * 3/2, mempages - 1);
    mempages -= reserve;

    names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
            SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);

    dcache_init();
    inode_init();
    files_init(mempages);
    mnt_init();
    bdev_cache_init();
    chrdev_init();
}