From: David Howells Date: Mon, 28 Aug 2006 08:15:37 -0400 NFS: Add dentry materialisation op 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 Signed-off-by: Trond Myklebust --- fs/dcache.c | 164 ++++++++++++++++++++++++++++++++++++++++++++---- include/linux/dcache.h | 1 2 files changed, 151 insertions(+), 14 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 1b4a3a3..17b392a 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -828,17 +828,19 @@ void d_instantiate(struct dentry *entry, * (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(stru 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 * e 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 * e 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); diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 471781f..44605be 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -221,6 +221,7 @@ static inline int dname_external(struct */ 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 */