libceph: use sizeof_footer() more

Don't open-code sizeof_footer() in read_partial_message() and
ceph_msg_revoke().  Also, after switching to sizeof_footer(), it's now
possible to use con_out_kvec_add() in prepare_write_message_footer().
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Alex Elder <elder@linaro.org>

net/ceph/messenger.c

@@ -1221,25 +1221,19 @@ static void prepare_message_data(struct ceph_msg *msg, u32 data_len)
 static void prepare_write_message_footer(struct ceph_connection *con)
 {
 	struct ceph_msg *m = con->out_msg;
-	int v = con->out_kvec_left;
 
 	m->footer.flags |= CEPH_MSG_FOOTER_COMPLETE;
 
 	dout("prepare_write_message_footer %p\n", con);
-	con->out_kvec[v].iov_base = &m->footer;
+	con_out_kvec_add(con, sizeof_footer(con), &m->footer);
 	if (con->peer_features & CEPH_FEATURE_MSG_AUTH) {
 		if (con->ops->sign_message)
 			con->ops->sign_message(m);
 		else
 			m->footer.sig = 0;
-		con->out_kvec[v].iov_len = sizeof(m->footer);
-		con->out_kvec_bytes += sizeof(m->footer);
 	} else {
 		m->old_footer.flags = m->footer.flags;
-		con->out_kvec[v].iov_len = sizeof(m->old_footer);
-		con->out_kvec_bytes += sizeof(m->old_footer);
 	}
-	con->out_kvec_left++;
 	con->out_more = m->more_to_follow;
 	con->out_msg_done = true;
 }
@@ -2409,11 +2403,7 @@ static int read_partial_message(struct ceph_connection *con)
 	}
 
 	/* footer */
-	if (need_sign)
-		size = sizeof(m->footer);
-	else
-		size = sizeof(m->old_footer);
-
+	size = sizeof_footer(con);
 	end += size;
 	ret = read_partial(con, end, size, &m->footer);
 	if (ret <= 0)
@@ -3089,10 +3079,7 @@ void ceph_msg_revoke(struct ceph_msg *msg)
 			con->out_skip += con_out_kvec_skip(con);
 		} else {
 			BUG_ON(!msg->data_length);
-			if (con->peer_features & CEPH_FEATURE_MSG_AUTH)
-				con->out_skip += sizeof(msg->footer);
-			else
-				con->out_skip += sizeof(msg->old_footer);
+			con->out_skip += sizeof_footer(con);
 		}
 		/* data, middle, front */
 		if (msg->data_length)