rbd: support for exclusive-lock feature

Add basic support for RBD_FEATURE_EXCLUSIVE_LOCK feature.  Maintenance
operations (resize, snapshot create, etc) are offloaded to librbd via
returning -EOPNOTSUPP - librbd should request the lock and execute the
operation.
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Tested-by: Mike Christie <mchristi@redhat.com>

drivers/block/rbd_types.h

@@ -28,6 +28,17 @@
 #define RBD_DATA_PREFIX        "rbd_data."
 #define RBD_ID_PREFIX          "rbd_id."
 
+#define RBD_LOCK_NAME          "rbd_lock"
+#define RBD_LOCK_TAG           "internal"
+#define RBD_LOCK_COOKIE_PREFIX "auto"
+
+enum rbd_notify_op {
+	RBD_NOTIFY_OP_ACQUIRED_LOCK      = 0,
+	RBD_NOTIFY_OP_RELEASED_LOCK      = 1,
+	RBD_NOTIFY_OP_REQUEST_LOCK       = 2,
+	RBD_NOTIFY_OP_HEADER_UPDATE      = 3,
+};
+
 /*
  * For format version 1, rbd image 'foo' consists of objects
  *   foo.rbd		- image metadata

net/ceph/ceph_strings.c

@@ -15,6 +15,7 @@ const char *ceph_entity_type_name(int type)
 	default: return "unknown";
 	}
 }
+EXPORT_SYMBOL(ceph_entity_type_name);
 
 const char *ceph_osd_op_name(int op)
 {