vfs: add d_prune dentry operation

This adds a d_prune dentry operation that is called by the VFS prior to
pruning (i.e. unhashing and killing) a hashed dentry from the dcache.
Wrap dentry_lru_del() and use the new _prune() helper in the cases where we
are about to unhash and kill the dentry.

This will be used by Ceph to maintain a flag indicating whether the
complete contents of a directory are contained in the dcache, allowing it
to satisfy lookups and readdir without addition server communication.

Renumber a few DCACHE_* #defines to group DCACHE_OP_PRUNE with the other
DCACHE_OP_ bits.

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Christoph Hellwig <hch@lst.de>

1 files changed, 35 insertions, 5 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index a88948b8bd17..274f13e2f094 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -225,7 +225,7 @@ static void dentry_unlink_inode(struct dentry * dentry)
 }
 
 /*
- * dentry_lru_(add|del|move_tail) must be called with d_lock held.
+ * dentry_lru_(add|del|prune|move_tail) must be called with d_lock held.
  */
 static void dentry_lru_add(struct dentry *dentry)
 {
@@ -245,6 +245,9 @@ static void __dentry_lru_del(struct dentry *dentry)
         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)) {
@@ -254,6 +257,23 @@ static void dentry_lru_del(struct dentry *dentry)
         }
 }
 
+/*
+ * 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_tail(struct dentry *dentry)
 {
         spin_lock(&dcache_lru_lock);
@@ -403,8 +423,12 @@ relock:
 
         if (ref)
                 dentry->d_count--;
-        /* if dentry was on the d_lru list delete it from there */
-        dentry_lru_del(dentry);
+        /*
+         * 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);
@@ -854,8 +878,12 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
                 do {
                         struct inode *inode;
 
-                        /* detach from the system */
-                        dentry_lru_del(dentry);
+                        /*
+                         * 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) {
@@ -1283,6 +1311,8 @@ void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
                 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);