ceph: add flags parameter to send_cap_msg

Add a flags parameter to send_cap_msg, so we can request expedited
service from the MDS when we know we'll be waiting on the result.

Set that flag in the case of try_flush_caps. The callers of that
function generally wait synchronously on the result, so it's beneficial
to ask the server to expedite it.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Yan, Zheng <zyan@redhat.com>

include/linux/ceph/ceph_fs.h

@@ -653,6 +653,9 @@ enum {
 
 extern const char *ceph_cap_op_name(int op);
 
+/* flags field in client cap messages (version >= 10) */
+#define CEPH_CLIENT_CAPS_SYNC	(0x1)
+
 /*
  * caps message, used for capability callbacks, acks, requests, etc.
  */