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NFS: Add dentry materialisation op

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The attached patch adds a new directory cache management function that prepares
a disconnected anonymous function to be connected into the dentry tree. The
anonymous dentry is transferred the name and parentage from another dentry.

The following changes were made in [try #2]:

 (*) d_materialise_dentry() now switches the parentage of the two nodes around
     correctly when one or other of them is self-referential.

The following changes were made in [try #7]:

 (*) d_instantiate_unique() has had the interior part split out as function
     __d_instantiate_unique(). Callers of this latter function must be holding
     the appropriate locks.

 (*) _d_rehash() has been added as a wrapper around __d_rehash() to call it
     with the most obvious hash list (the one from the name). d_rehash() now
     calls _d_rehash().

 (*) d_materialise_dentry() is now __d_materialise_dentry() and is static.

 (*) d_materialise_unique() added to perform the combination of d_find_alias(),
     d_materialise_dentry() and d_add_unique() that the NFS client was doing
     twice, all within a single dcache_lock critical section. This reduces the
     number of times two different spinlocks were being accessed.

The following further changes were made:

 (*) Add the dentries onto their parents d_subdirs lists.

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
This commit is contained in:
David Howells 2006-08-22 20:06:07 -04:00 committed by Trond Myklebust
parent 979df72e6f
commit 770bfad846
2 changed files with 151 additions and 14 deletions
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164
fs/dcache.c
View file

@ -828,17 +828,19 @@ void d_instantiate(struct dentry *entry, struct inode * inode)
* (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)
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;
BUG_ON(!list_empty(&entry->d_alias));
spin_lock(&dcache_lock);
if (!inode)
goto do_negative;
if (!inode) {
entry->d_inode = NULL;
return NULL;
}
list_for_each_entry(alias, &inode->i_dentry, d_alias) {
struct qstr *qstr = &alias->d_name;
@ -851,19 +853,35 @@ struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
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;
}
struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
{
struct dentry *result;
BUG_ON(!list_empty(&entry->d_alias));
spin_lock(&dcache_lock);
result = __d_instantiate_unique(entry, inode);
spin_unlock(&dcache_lock);
if (!result) {
security_d_instantiate(entry, inode);
return NULL;
}
BUG_ON(!d_unhashed(result));
iput(inode);
return result;
}
EXPORT_SYMBOL(d_instantiate_unique);
/**
@ -1235,6 +1253,11 @@ static void __d_rehash(struct dentry * entry, struct hlist_head *list)
hlist_add_head_rcu(&entry->d_hash, list);
}
static void _d_rehash(struct dentry * entry)
{
__d_rehash(entry, d_hash(entry->d_parent, entry->d_name.hash));
}
/**
* d_rehash - add an entry back to the hash
* @entry: dentry to add to the hash
@ -1244,11 +1267,9 @@ static void __d_rehash(struct dentry * entry, struct hlist_head *list)
void d_rehash(struct dentry * entry)
{
struct hlist_head *list = d_hash(entry->d_parent, entry->d_name.hash);
spin_lock(&dcache_lock);
spin_lock(&entry->d_lock);
__d_rehash(entry, list);
_d_rehash(entry);
spin_unlock(&entry->d_lock);
spin_unlock(&dcache_lock);
}
@ -1386,6 +1407,120 @@ already_unhashed:
spin_unlock(&dcache_lock);
}
/*
* Prepare an anonymous dentry for life in the superblock's dentry tree as a
* named dentry in place of the dentry to be replaced.
*/
static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
{
struct dentry *dparent, *aparent;
switch_names(dentry, anon);
do_switch(dentry->d_name.len, anon->d_name.len);
do_switch(dentry->d_name.hash, anon->d_name.hash);
dparent = dentry->d_parent;
aparent = anon->d_parent;
dentry->d_parent = (aparent == anon) ? dentry : aparent;
list_del(&dentry->d_u.d_child);
if (!IS_ROOT(dentry))
list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
else
INIT_LIST_HEAD(&dentry->d_u.d_child);
anon->d_parent = (dparent == dentry) ? anon : dparent;
list_del(&anon->d_u.d_child);
if (!IS_ROOT(anon))
list_add(&anon->d_u.d_child, &anon->d_parent->d_subdirs);
else
INIT_LIST_HEAD(&anon->d_u.d_child);
anon->d_flags &= ~DCACHE_DISCONNECTED;
}
/**
* d_materialise_unique - introduce an inode into the tree
* @dentry: candidate dentry
* @inode: inode to bind to the dentry, to which aliases may be attached
*
* Introduces an dentry into the tree, substituting an extant disconnected
* root directory alias in its place if there is one
*/
struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
{
struct dentry *alias, *actual;
BUG_ON(!d_unhashed(dentry));
spin_lock(&dcache_lock);
if (!inode) {
actual = dentry;
dentry->d_inode = NULL;
goto found_lock;
}
/* See if a disconnected directory already exists as an anonymous root
* that we should splice into the tree instead */
if (S_ISDIR(inode->i_mode) && (alias = __d_find_alias(inode, 1))) {
spin_lock(&alias->d_lock);
/* Is this a mountpoint that we could splice into our tree? */
if (IS_ROOT(alias))
goto connect_mountpoint;
if (alias->d_name.len == dentry->d_name.len &&
alias->d_parent == dentry->d_parent &&
memcmp(alias->d_name.name,
dentry->d_name.name,
dentry->d_name.len) == 0)
goto replace_with_alias;
spin_unlock(&alias->d_lock);
/* Doh! Seem to be aliasing directories for some reason... */
dput(alias);
}
/* Add a unique reference */
actual = __d_instantiate_unique(dentry, inode);
if (!actual)
actual = dentry;
else if (unlikely(!d_unhashed(actual)))
goto shouldnt_be_hashed;
found_lock:
spin_lock(&actual->d_lock);
found:
_d_rehash(actual);
spin_unlock(&actual->d_lock);
spin_unlock(&dcache_lock);
if (actual == dentry) {
security_d_instantiate(dentry, inode);
return NULL;
}
iput(inode);
return actual;
/* Convert the anonymous/root alias into an ordinary dentry */
connect_mountpoint:
__d_materialise_dentry(dentry, alias);
/* Replace the candidate dentry with the alias in the tree */
replace_with_alias:
__d_drop(alias);
actual = alias;
goto found;
shouldnt_be_hashed:
spin_unlock(&dcache_lock);
BUG();
goto shouldnt_be_hashed;
}
/**
* d_path - return the path of a dentry
* @dentry: dentry to report
@ -1784,6 +1919,7 @@ EXPORT_SYMBOL(d_instantiate);
EXPORT_SYMBOL(d_invalidate);
EXPORT_SYMBOL(d_lookup);
EXPORT_SYMBOL(d_move);
EXPORT_SYMBOL_GPL(d_materialise_unique);
EXPORT_SYMBOL(d_path);
EXPORT_SYMBOL(d_prune_aliases);
EXPORT_SYMBOL(d_rehash);

1
include/linux/dcache.h
View file

@ -221,6 +221,7 @@ static inline int dname_external(struct dentry *dentry)
*/
extern void d_instantiate(struct dentry *, struct inode *);
extern struct dentry * d_instantiate_unique(struct dentry *, struct inode *);
extern struct dentry * d_materialise_unique(struct dentry *, struct inode *);
extern void d_delete(struct dentry *);
/* allocate/de-allocate */