ocfs2: Add new cluster lock type

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 cluster lock type which OCFS2 can attach to
dentries.  A small number of fs/ocfs2/dcache.c functions are stubbed
out so that this change can compile.

Signed-off-by: Mark Fasheh <[email protected]>

fs/ocfs2/dcache.c

@@ -87,6 +87,8 @@ static int ocfs2_dentry_revalidate(struct dentry *dentry,
 	return ret;
 }
 
+DEFINE_SPINLOCK(dentry_attach_lock);
+
 struct dentry_operations ocfs2_dentry_ops = {
 	.d_revalidate		= ocfs2_dentry_revalidate,
 };

fs/ocfs2/dcache.h

@@ -28,4 +28,31 @@
 
 extern struct dentry_operations ocfs2_dentry_ops;
 
+struct ocfs2_dentry_lock {
+	unsigned int		dl_count;
+	u64			dl_parent_blkno;
+
+	/*
+	 * The ocfs2_dentry_lock keeps an inode reference until
+	 * dl_lockres has been destroyed. This is usually done in
+	 * ->d_iput() anyway, so there should be minimal impact.
+	 */
+	struct inode		*dl_inode;
+	struct ocfs2_lock_res	dl_lockres;
+};
+
+static inline void ocfs2_dentry_lock_put(struct ocfs2_super *osb,
+					 struct ocfs2_dentry_lock *dl)
+{
+}
+
+static inline struct dentry *ocfs2_find_local_alias(struct inode *inode,
+						    u64 parent_blkno,
+						    int skip_unhashed)
+{
+	return NULL;
+}
+
+extern spinlock_t dentry_attach_lock;
+
 #endif /* OCFS2_DCACHE_H */