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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/config.h>
#include <linux/syscalls.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/fsnotify.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/smp_lock.h>
#include <linux/hash.h>
#include <linux/cache.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/file.h>
#include <asm/uaccess.h>
#include <linux/security.h>
#include <linux/seqlock.h>
#include <linux/swap.h>
#include <linux/bootmem.h>
/* #define DCACHE_DEBUG 1 */
int sysctl_vfs_cache_pressure = 100;
EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
__cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lock);
static seqlock_t rename_lock __cacheline_aligned_in_smp = SEQLOCK_UNLOCKED;
EXPORT_SYMBOL(dcache_lock);
static kmem_cache_t *dentry_cache;
#define DNAME_INLINE_LEN (sizeof(struct dentry)-offsetof(struct dentry,d_iname))
/*
* This is the single most critical data structure when it comes
* to the dcache: the hashtable for lookups. Somebody should try
* to make this good - I've just made it work.
*
* This hash-function tries to avoid losing too many bits of hash
* information, yet avoid using a prime hash-size or similar.
*/
#define D_HASHBITS d_hash_shift
#define D_HASHMASK d_hash_mask
static unsigned int d_hash_mask;
static unsigned int d_hash_shift;
static struct hlist_head *dentry_hashtable;
static LIST_HEAD(dentry_unused);
/* Statistics gathering. */
struct dentry_stat_t dentry_stat = {
.age_limit = 45,
};
static void d_callback(struct rcu_head *head)
{
struct dentry * dentry = container_of(head, struct dentry, d_u.d_rcu);
if (dname_external(dentry))
kfree(dentry->d_name.name);
kmem_cache_free(dentry_cache, dentry);
}
/*
* no dcache_lock, please. The caller must decrement dentry_stat.nr_dentry
* inside dcache_lock.
*/
static void d_free(struct dentry *dentry)
{
if (dentry->d_op && dentry->d_op->d_release)
dentry->d_op->d_release(dentry);
call_rcu(&dentry->d_u.d_rcu, d_callback);
}
/*
* Release the dentry's inode, using the filesystem
* d_iput() operation if defined.
* Called with dcache_lock and per dentry lock held, drops both.
*/
static void dentry_iput(struct dentry * dentry)
{
struct inode *inode = dentry->d_inode;
if (inode) {
dentry->d_inode = NULL;
list_del_init(&dentry->d_alias);
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
if (!inode->i_nlink)
fsnotify_inoderemove(inode);
if (dentry->d_op && dentry->d_op->d_iput)
dentry->d_op->d_iput(dentry, inode);
else
iput(inode);
} else {
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
}
}
/*
* This is dput
*
* This is complicated by the fact that we do not want to put
* dentries that are no longer on any hash chain on the unused
* list: we'd much rather just get rid of them immediately.
*
* However, that implies that we have to traverse the dentry
* tree upwards to the parents which might _also_ now be
* scheduled for deletion (it may have been only waiting for
* its last child to go away).
*
* This tail recursion is done by hand as we don't want to depend
* on the compiler to always get this right (gcc generally doesn't).
* Real recursion would eat up our stack space.
*/
/*
* dput - release a dentry
* @dentry: dentry to release
*
* Release a dentry. This will drop the usage count and if appropriate
* call the dentry unlink method as well as removing it from the queues and
* releasing its resources. If the parent dentries were scheduled for release
* they too may now get deleted.
*
* no dcache lock, please.
*/
void dput(struct dentry *dentry)
{
if (!dentry)
return;
repeat:
if (atomic_read(&dentry->d_count) == 1)
might_sleep();
if (!atomic_dec_and_lock(&dentry->d_count, &dcache_lock))
return;
spin_lock(&dentry->d_lock);
if (atomic_read(&dentry->d_count)) {
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
return;
}
/*
* AV: ->d_delete() is _NOT_ allowed to block now.
*/
if (dentry->d_op && dentry->d_op->d_delete) {
if (dentry->d_op->d_delete(dentry))
goto unhash_it;
}
/* Unreachable? Get rid of it */
if (d_unhashed(dentry))
goto kill_it;
if (list_empty(&dentry->d_lru)) {
dentry->d_flags |= DCACHE_REFERENCED;
list_add(&dentry->d_lru, &dentry_unused);
dentry_stat.nr_unused++;
}
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
return;
unhash_it:
__d_drop(dentry);
kill_it: {
struct dentry *parent;
/* If dentry was on d_lru list
* delete it from there
*/
if (!list_empty(&dentry->d_lru)) {
list_del(&dentry->d_lru);
dentry_stat.nr_unused--;
}
list_del(&dentry->d_u.d_child);
dentry_stat.nr_dentry--; /* For d_free, below */
/*drops the locks, at that point nobody can reach this dentry */
dentry_iput(dentry);
parent = dentry->d_parent;
d_free(dentry);
if (dentry == parent)
return;
dentry = parent;
goto repeat;
}
}
/**
* d_invalidate - invalidate a dentry
* @dentry: dentry to invalidate
*
* Try to invalidate the dentry if it turns out to be
* possible. If there are other dentries that can be
* reached through this one we can't delete it and we
* return -EBUSY. On success we return 0.
*
* no dcache lock.
*/
int d_invalidate(struct dentry * dentry)
{
/*
* If it's already been dropped, return OK.
*/
spin_lock(&dcache_lock);
if (d_unhashed(dentry)) {
spin_unlock(&dcache_lock);
return 0;
}
/*
* Check whether to do a partial shrink_dcache
* to get rid of unused child entries.
*/
if (!list_empty(&dentry->d_subdirs)) {
spin_unlock(&dcache_lock);
shrink_dcache_parent(dentry);
spin_lock(&dcache_lock);
}
/*
* Somebody else still using it?
*
* If it's a directory, we can't drop it
* for fear of somebody re-populating it
* with children (even though dropping it
* would make it unreachable from the root,
* we might still populate it if it was a
* working directory or similar).
*/
spin_lock(&dentry->d_lock);
if (atomic_read(&dentry->d_count) > 1) {
if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) {
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
return -EBUSY;
}
}
__d_drop(dentry);
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
return 0;
}
/* This should be called _only_ with dcache_lock held */
static inline struct dentry * __dget_locked(struct dentry *dentry)
{
atomic_inc(&dentry->d_count);
if (!list_empty(&dentry->d_lru)) {
dentry_stat.nr_unused--;
list_del_init(&dentry->d_lru);
}
return dentry;
}
struct dentry * dget_locked(struct dentry *dentry)
{
return __dget_locked(dentry);
}
/**
* d_find_alias - grab a hashed alias of inode
* @inode: inode in question
* @want_discon: flag, used by d_splice_alias, to request
* that only a DISCONNECTED alias be returned.
*
* If inode has a hashed alias, or is a directory and has any alias,
* acquire the reference to alias and return it. Otherwise return NULL.
* Notice that if inode is a directory there can be only one alias and
* it can be unhashed only if it has no children, or if it is the root
* of a filesystem.
*
* If the inode has a DCACHE_DISCONNECTED alias, then prefer
* any other hashed alias over that one unless @want_discon is set,
* in which case only return a DCACHE_DISCONNECTED alias.
*/
static struct dentry * __d_find_alias(struct inode *inode, int want_discon)
{
struct list_head *head, *next, *tmp;
struct dentry *alias, *discon_alias=NULL;
head = &inode->i_dentry;
next = inode->i_dentry.next;
while (next != head) {
tmp = next;
next = tmp->next;
prefetch(next);
alias = list_entry(tmp, struct dentry, d_alias);
if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
if (alias->d_flags & DCACHE_DISCONNECTED)
discon_alias = alias;
else if (!want_discon) {
__dget_locked(alias);
return alias;
}
}
}
if (discon_alias)
__dget_locked(discon_alias);
return discon_alias;
}
struct dentry * d_find_alias(struct inode *inode)
{
struct dentry *de = NULL;
if (!list_empty(&inode->i_dentry)) {
spin_lock(&dcache_lock);
de = __d_find_alias(inode, 0);
spin_unlock(&dcache_lock);
}
return de;
}
/*
* Try to kill dentries associated with this inode.
* WARNING: you must own a reference to inode.
*/
void d_prune_aliases(struct inode *inode)
{
struct dentry *dentry;
restart:
spin_lock(&dcache_lock);
list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
spin_lock(&dentry->d_lock);
if (!atomic_read(&dentry->d_count)) {
__dget_locked(dentry);
__d_drop(dentry);
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
dput(dentry);
goto restart;
}
spin_unlock(&dentry->d_lock);
}
spin_unlock(&dcache_lock);
}
/*
* Throw away a dentry - free the inode, dput the parent.
* This requires that the LRU list has already been
* removed.
* Called with dcache_lock, drops it and then regains.
*/
static inline void prune_one_dentry(struct dentry * dentry)
{
struct dentry * parent;
__d_drop(dentry);
list_del(&dentry->d_u.d_child);
dentry_stat.nr_dentry--; /* For d_free, below */
dentry_iput(dentry);
parent = dentry->d_parent;
d_free(dentry);
if (parent != dentry)
dput(parent);
spin_lock(&dcache_lock);
}
/**
* prune_dcache - shrink the dcache
* @count: number of entries to try and free
*
* Shrink the dcache. This is done when we need
* more memory, or simply when we need to unmount
* something (at which point we need to unuse
* all dentries).
*
* This function may fail to free any resources if
* all the dentries are in use.
*/
static void prune_dcache(int count)
{
spin_lock(&dcache_lock);
for (; count ; count--) {
struct dentry *dentry;
struct list_head *tmp;
cond_resched_lock(&dcache_lock);
tmp = dentry_unused.prev;
if (tmp == &dentry_unused)
break;
list_del_init(tmp);
prefetch(dentry_unused.prev);
dentry_stat.nr_unused--;
dentry = list_entry(tmp, struct dentry, d_lru);
spin_lock(&dentry->d_lock);
/*
* We found an inuse dentry which was not removed from
* dentry_unused because of laziness during lookup. Do not free
* it - just keep it off the dentry_unused list.
*/
if (atomic_read(&dentry->d_count)) {
spin_unlock(&dentry->d_lock);
continue;
}
/* If the dentry was recently referenced, don't free it. */
if (dentry->d_flags & DCACHE_REFERENCED) {
dentry->d_flags &= ~DCACHE_REFERENCED;
list_add(&dentry->d_lru, &dentry_unused);
dentry_stat.nr_unused++;
spin_unlock(&dentry->d_lock);
continue;
}
prune_one_dentry(dentry);
}
spin_unlock(&dcache_lock);
}
/*
* Shrink the dcache for the specified super block.
* This allows us to unmount a device without disturbing
* the dcache for the other devices.
*
* This implementation makes just two traversals of the
* unused list. On the first pass we move the selected
* dentries to the most recent end, and on the second
* pass we free them. The second pass must restart after
* each dput(), but since the target dentries are all at
* the end, it's really just a single traversal.
*/
/**
* shrink_dcache_sb - shrink dcache for a superblock
* @sb: superblock
*
* Shrink the dcache for the specified super block. This
* is used to free the dcache before unmounting a file
* system
*/
void shrink_dcache_sb(struct super_block * sb)
{
struct list_head *tmp, *next;
struct dentry *dentry;
/*
* Pass one ... move the dentries for the specified
* superblock to the most recent end of the unused list.
*/
spin_lock(&dcache_lock);
list_for_each_safe(tmp, next, &dentry_unused) {
dentry = list_entry(tmp, struct dentry, d_lru);
if (dentry->d_sb != sb)
continue;
list_del(tmp);
list_add(tmp, &dentry_unused);
}
/*
* Pass two ... free the dentries for this superblock.
*/
repeat:
list_for_each_safe(tmp, next, &dentry_unused) {
dentry = list_entry(tmp, struct dentry, d_lru);
if (dentry->d_sb != sb)
continue;
dentry_stat.nr_unused--;
list_del_init(tmp);
spin_lock(&dentry->d_lock);
if (atomic_read(&dentry->d_count)) {
spin_unlock(&dentry->d_lock);
continue;
}
prune_one_dentry(dentry);
goto repeat;
}
spin_unlock(&dcache_lock);
}
/*
* Search for at least 1 mount point in the dentry's subdirs.
* We descend to the next level whenever the d_subdirs
* list is non-empty and continue searching.
*/
/**
* have_submounts - check for mounts over a dentry
* @parent: dentry to check.
*
* Return true if the parent or its subdirectories contain
* a mount point
*/
int have_submounts(struct dentry *parent)
{
struct dentry *this_parent = parent;
struct list_head *next;
spin_lock(&dcache_lock);
if (d_mountpoint(parent))
goto positive;
repeat:
next = this_parent->d_subdirs.next;
resume:
while (next != &this_parent->d_subdirs) {
struct list_head *tmp = next;
struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
next = tmp->next;
/* Have we found a mount point ? */
if (d_mountpoint(dentry))
goto positive;
if (!list_empty(&dentry->d_subdirs)) {
this_parent = dentry;
goto repeat;
}
}
/*
* All done at this level ... ascend and resume the search.
*/
if (this_parent != parent) {
next = this_parent->d_u.d_child.next;
this_parent = this_parent->d_parent;
goto resume;
}
spin_unlock(&dcache_lock);
return 0; /* No mount points found in tree */
positive:
spin_unlock(&dcache_lock);
return 1;
}
/*
* Search the dentry child list for the specified parent,
* and move any unused dentries to the end of the unused
* list for prune_dcache(). We descend to the next level
* whenever the d_subdirs list is non-empty and continue
* searching.
*
* It returns zero iff there are no unused children,
* otherwise it returns the number of children moved to
* the end of the unused list. This may not be the total
* number of unused children, because select_parent can
* drop the lock and return early due to latency
* constraints.
*/
static int select_parent(struct dentry * parent)
{
struct dentry *this_parent = parent;
struct list_head *next;
int found = 0;
spin_lock(&dcache_lock);
repeat:
next = this_parent->d_subdirs.next;
resume:
while (next != &this_parent->d_subdirs) {
struct list_head *tmp = next;
struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
next = tmp->next;
if (!list_empty(&dentry->d_lru)) {
dentry_stat.nr_unused--;
list_del_init(&dentry->d_lru);
}
/*
* move only zero ref count dentries to the end
* of the unused list for prune_dcache
*/
if (!atomic_read(&dentry->d_count)) {
list_add(&dentry->d_lru, dentry_unused.prev);
dentry_stat.nr_unused++;
found++;
}
/*
* We can return to the caller if we have found some (this
* ensures forward progress). We'll be coming back to find
* the rest.
*/
if (found && need_resched())
goto out;
/*
* Descend a level if the d_subdirs list is non-empty.
*/
if (!list_empty(&dentry->d_subdirs)) {
this_parent = dentry;
#ifdef DCACHE_DEBUG
printk(KERN_DEBUG "select_parent: descending to %s/%s, found=%d\n",
dentry->d_parent->d_name.name, dentry->d_name.name, found);
#endif
goto repeat;
}
}
/*
* All done at this level ... ascend and resume the search.
*/
if (this_parent != parent) {
next = this_parent->d_u.d_child.next;
this_parent = this_parent->d_parent;
#ifdef DCACHE_DEBUG
printk(KERN_DEBUG "select_parent: ascending to %s/%s, found=%d\n",
this_parent->d_parent->d_name.name, this_parent->d_name.name, found);
#endif
goto resume;
}
out:
spin_unlock(&dcache_lock);
return found;
}
/**
* shrink_dcache_parent - prune dcache
* @parent: parent of entries to prune
*
* Prune the dcache to remove unused children of the parent dentry.
*/
void shrink_dcache_parent(struct dentry * parent)
{
int found;
while ((found = select_parent(parent)) != 0)
prune_dcache(found);
}
/**
* shrink_dcache_anon - further prune the cache
* @head: head of d_hash list of dentries to prune
*
* Prune the dentries that are anonymous
*
* parsing d_hash list does not hlist_for_each_entry_rcu() as it
* done under dcache_lock.
*
*/
void shrink_dcache_anon(struct hlist_head *head)
{
struct hlist_node *lp;
int found;
do {
found = 0;
spin_lock(&dcache_lock);
hlist_for_each(lp, head) {
struct dentry *this = hlist_entry(lp, struct dentry, d_hash);
if (!list_empty(&this->d_lru)) {
dentry_stat.nr_unused--;
list_del_init(&this->d_lru);
}
/*
* move only zero ref count dentries to the end
* of the unused list for prune_dcache
*/
if (!atomic_read(&this->d_count)) {
list_add_tail(&this->d_lru, &dentry_unused);
dentry_stat.nr_unused++;
found++;
}
}
spin_unlock(&dcache_lock);
prune_dcache(found);
} while(found);
}
/*
* Scan `nr' dentries and return the number which remain.
*
* We need to avoid reentering the filesystem if the caller is performing a
* GFP_NOFS allocation attempt. One example deadlock is:
*
* ext2_new_block->getblk->GFP->shrink_dcache_memory->prune_dcache->
* prune_one_dentry->dput->dentry_iput->iput->inode->i_sb->s_op->put_inode->
* ext2_discard_prealloc->ext2_free_blocks->lock_super->DEADLOCK.
*
* In this case we return -1 to tell the caller that we baled.
*/
static int shrink_dcache_memory(int nr, gfp_t gfp_mask)
{
if (nr) {
if (!(gfp_mask & __GFP_FS))
return -1;
prune_dcache(nr);
}
return (dentry_stat.nr_unused / 100) * sysctl_vfs_cache_pressure;
}
/**
* d_alloc - allocate a dcache entry
* @parent: parent of entry to allocate
* @name: qstr of the name
*
* Allocates a dentry. It returns %NULL if there is insufficient memory
* available. On a success the dentry is returned. The name passed in is
* copied and the copy passed in may be reused after this call.
*/
struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
{
struct dentry *dentry;
char *dname;
dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
if (!dentry)
return NULL;
if (name->len > DNAME_INLINE_LEN-1) {
dname = kmalloc(name->len + 1, GFP_KERNEL);
if (!dname) {
kmem_cache_free(dentry_cache, dentry);
return NULL;
}
} else {
dname = dentry->d_iname;
}
dentry->d_name.name = dname;
dentry->d_name.len = name->len;
dentry->d_name.hash = name->hash;
memcpy(dname, name->name, name->len);
dname[name->len] = 0;
atomic_set(&dentry->d_count, 1);
dentry->d_flags = DCACHE_UNHASHED;
spin_lock_init(&dentry->d_lock);
dentry->d_inode = NULL;
dentry->d_parent = NULL;
dentry->d_sb = NULL;
dentry->d_op = NULL;
dentry->d_fsdata = NULL;
dentry->d_mounted = 0;
#ifdef CONFIG_PROFILING
dentry->d_cookie = NULL;
#endif
INIT_HLIST_NODE(&dentry->d_hash);
INIT_LIST_HEAD(&dentry->d_lru);
INIT_LIST_HEAD(&dentry->d_subdirs);
INIT_LIST_HEAD(&dentry->d_alias);
if (parent) {
dentry->d_parent = dget(parent);
dentry->d_sb = parent->d_sb;
} else {
INIT_LIST_HEAD(&dentry->d_u.d_child);
}
spin_lock(&dcache_lock);
if (parent)
list_add(&dentry->d_u.d_child, &parent->d_subdirs);
dentry_stat.nr_dentry++;
spin_unlock(&dcache_lock);
return dentry;
}
struct dentry *d_alloc_name(struct dentry *parent, const char *name)
{
struct qstr q;
q.name = name;
q.len = strlen(name);
q.hash = full_name_hash(q.name, q.len);
return d_alloc(parent, &q);
}
/**
* d_instantiate - fill in inode information for a dentry
* @entry: dentry to complete
* @inode: inode to attach to this dentry
*
* Fill in inode information in the entry.
*
* This turns negative dentries into productive full members
* of society.
*
* NOTE! This assumes that the inode count has been incremented
* (or otherwise set) by the caller to indicate that it is now
* in use by the dcache.
*/
void d_instantiate(struct dentry *entry, struct inode * inode)
{
if (!list_empty(&entry->d_alias)) BUG();
spin_lock(&dcache_lock);
if (inode)
list_add(&entry->d_alias, &inode->i_dentry);
entry->d_inode = inode;
fsnotify_d_instantiate(entry, inode);
spin_unlock(&dcache_lock);
security_d_instantiate(entry, inode);
}
/**
* d_instantiate_unique - instantiate a non-aliased dentry
* @entry: dentry to instantiate
* @inode: inode to attach to this dentry
*
* Fill in inode information in the entry. On success, it returns NULL.
* If an unhashed alias of "entry" already exists, then we return the
* aliased dentry instead and drop one reference to inode.
*
* Note that in order to avoid conflicts with rename() etc, the caller
* had better be holding the parent directory semaphore.
*
* This also assumes that the inode count has been incremented
* (or otherwise set) by the caller to indicate that it is now
* in use by the dcache.
*/
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;
BUG_ON(!list_empty(&entry->d_alias));
spin_lock(&dcache_lock);
if (!inode)
goto do_negative;
list_for_each_entry(alias, &inode->i_dentry, d_alias) {
struct qstr *qstr = &alias->d_name;
if (qstr->hash != hash)
continue;
if (alias->d_parent != entry->d_parent)
continue;
if (qstr->len != len)
continue;
if (memcmp(qstr->name, name, len))
continue;
dget_locked(alias);
spin_unlock(&dcache_lock);
BUG_ON(!d_unhashed(alias));
iput(inode);
return alias;
}
list_add(&entry->d_alias, &inode->i_dentry);
do_negative:
entry->d_inode = inode;
fsnotify_d_instantiate(entry, inode);
spin_unlock(&dcache_lock);
security_d_instantiate(entry, inode);
return NULL;
}
EXPORT_SYMBOL(d_instantiate_unique);
/**
* d_alloc_root - allocate root dentry
* @root_inode: inode to allocate the root for
*
* Allocate a root ("/") dentry for the inode given. The inode is
* instantiated and returned. %NULL is returned if there is insufficient
* memory or the inode passed is %NULL.
*/
struct dentry * d_alloc_root(struct inode * root_inode)
{
struct dentry *res = NULL;
if (root_inode) {
static const struct qstr name = { .name = "/", .len = 1 };
res = d_alloc(NULL, &name);
if (res) {
res->d_sb = root_inode->i_sb;
res->d_parent = res;
d_instantiate(res, root_inode);
}
}
return res;
}
static inline struct hlist_head *d_hash(struct dentry *parent,
unsigned long hash)
{
hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES;
hash = hash ^ ((hash ^ GOLDEN_RATIO_PRIME) >> D_HASHBITS);
return dentry_hashtable + (hash & D_HASHMASK);
}
/**
* d_alloc_anon - allocate an anonymous dentry
* @inode: inode to allocate the dentry for
*
* This is similar to d_alloc_root. It is used by filesystems when
* creating a dentry for a given inode, often in the process of
* mapping a filehandle to a dentry. The returned dentry may be
* anonymous, or may have a full name (if the inode was already
* in the cache). The file system may need to make further
* efforts to connect this dentry into the dcache properly.
*
* When called on a directory inode, we must ensure that
* the inode only ever has one dentry. If a dentry is
* found, that is returned instead of allocating a new one.
*
* On successful return, the reference to the inode has been transferred
* to the dentry. If %NULL is returned (indicating kmalloc failure),
* the reference on the inode has not been released.
*/
struct dentry * d_alloc_anon(struct inode *inode)
{
static const struct qstr anonstring = { .name = "" };
struct dentry *tmp;
struct dentry *res;
if ((res = d_find_alias(inode))) {
iput(inode);
return res;
}
tmp = d_alloc(NULL, &anonstring);
if (!tmp)
return NULL;
tmp->d_parent = tmp; /* make sure dput doesn't croak */
spin_lock(&dcache_lock);
res = __d_find_alias(inode, 0);
if (!res) {
/* attach a disconnected dentry */
res = tmp;
tmp = NULL;
spin_lock(&res->d_lock);
res->d_sb = inode->i_sb;
res->d_parent = res;
res->d_inode = inode;
res->d_flags |= DCACHE_DISCONNECTED;
res->d_flags &= ~DCACHE_UNHASHED;
list_add(&res->d_alias, &inode->i_dentry);
hlist_add_head(&res->d_hash, &inode->i_sb->s_anon);
spin_unlock(&res->d_lock);
inode = NULL; /* don't drop reference */
}
spin_unlock(&dcache_lock);
if (inode)
iput(inode);
if (tmp)
dput(tmp);
return res;
}
/**
* d_splice_alias - splice a disconnected dentry into the tree if one exists
* @inode: the inode which may have a disconnected dentry
* @dentry: a negative dentry which we want to point to the inode.
*
* If inode is a directory and has a 'disconnected' dentry (i.e. IS_ROOT and
* DCACHE_DISCONNECTED), then d_move that in place of the given dentry
* and return it, else simply d_add the inode to the dentry and return NULL.
*
* This is needed in the lookup routine of any filesystem that is exportable
* (via knfsd) so that we can build dcache paths to directories effectively.
*
* If a dentry was found and moved, then it is returned. Otherwise NULL
* is returned. This matches the expected return value of ->lookup.
*
*/
struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
{
struct dentry *new = NULL;
if (inode) {
spin_lock(&dcache_lock);
new = __d_find_alias(inode, 1);
if (new) {
BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));
fsnotify_d_instantiate(new, inode);
spin_unlock(&dcache_lock);
security_d_instantiate(new, inode);
d_rehash(dentry);
d_move(new, dentry);
iput(inode);
} else {
/* d_instantiate takes dcache_lock, so we do it by hand */
list_add(&dentry->d_alias, &inode->i_dentry);
dentry->d_inode = inode;
fsnotify_d_instantiate(dentry, inode);
spin_unlock(&dcache_lock);
security_d_instantiate(dentry, inode);