ocfs2: Add dentry tracking API

Replace the dentry vote mechanism with a cluster lock which covers a set
of dentries. This allows us to force d_delete() only on nodes which actually
care about an unlink.

Every node that does a ->lookup() gets a read only lock on the dentry, until
an unlink during which the unlinking node, will request an exclusive lock,
forcing the other nodes who care about that dentry to d_delete() it. The
effect is that we retain a very lightweight ->d_revalidate(), and at the
same time get to make large improvements to the average case performance of
the ocfs2 unlink and rename operations.

This patch adds the higher level API and the dentry manipulation code.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

fs/ocfs2/dcache.h

@@ -41,17 +41,17 @@ struct ocfs2_dentry_lock {
 	struct ocfs2_lock_res	dl_lockres;
 };
 
-static inline void ocfs2_dentry_lock_put(struct ocfs2_super *osb,
-					 struct ocfs2_dentry_lock *dl)
-{
-}
+int ocfs2_dentry_attach_lock(struct dentry *dentry, struct inode *inode,
+			     u64 parent_blkno, int create);
 
-static inline struct dentry *ocfs2_find_local_alias(struct inode *inode,
-						    u64 parent_blkno,
-						    int skip_unhashed)
-{
-	return NULL;
-}
+void ocfs2_dentry_lock_put(struct ocfs2_super *osb,
+			   struct ocfs2_dentry_lock *dl);
+
+struct dentry *ocfs2_find_local_alias(struct inode *inode, u64 parent_blkno,
+				      int skip_unhashed);
+
+void ocfs2_dentry_move(struct dentry *dentry, struct dentry *target,
+		       struct inode *old_dir, struct inode *new_dir);
 
 extern spinlock_t dentry_attach_lock;