ceph: new cap message flags indicate if there is pending capsnap

These flags tell mds if there is pending capsnap explicitly.
Without this explicit notification, mds can only conclude if
client has pending capsnap. The method mds use is inefficient
and error-prone.
Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/caps.c

@@ -1248,7 +1248,10 @@ static int __send_cap(struct ceph_mds_client *mdsc, struct ceph_cap *cap,
 	arg.mode = inode->i_mode;
 
 	arg.inline_data = ci->i_inline_version != CEPH_INLINE_NONE;
-	arg.flags = 0;
+	if (list_empty(&ci->i_cap_snaps))
+		arg.flags = CEPH_CLIENT_CAPS_NO_CAPSNAP;
+	else
+		arg.flags = CEPH_CLIENT_CAPS_PENDING_CAPSNAP;
 	if (sync)
 		arg.flags |= CEPH_CLIENT_CAPS_SYNC;
 

include/linux/ceph/ceph_fs.h

@@ -669,7 +669,9 @@ enum {
 extern const char *ceph_cap_op_name(int op);
 
 /* flags field in client cap messages (version >= 10) */
-#define CEPH_CLIENT_CAPS_SYNC	(0x1)
+#define CEPH_CLIENT_CAPS_SYNC			(1<<0)
+#define CEPH_CLIENT_CAPS_NO_CAPSNAP		(1<<1)
+#define CEPH_CLIENT_CAPS_PENDING_CAPSNAP	(1<<2);
 
 /*
  * caps message, used for capability callbacks, acks, requests, etc.