ceph: reset front len on return to msgpool; BUG on mismatched front iov

Reset msg front len when a message is returned to the pool: the caller
may have changed it.

BUG if we try to send a message with a hdr.front_len that doesn't match
the front iov.
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/messenger.c

@@ -1954,6 +1954,8 @@ void ceph_con_send(struct ceph_connection *con, struct ceph_msg *msg)
 	msg->hdr.src.addr = con->msgr->my_enc_addr;
 	msg->hdr.orig_src = msg->hdr.src;
 
+	BUG_ON(msg->front.iov_len != le32_to_cpu(msg->hdr.front_len));
+
 	/* queue */
 	mutex_lock(&con->mutex);
 	BUG_ON(!list_empty(&msg->list_head));

fs/ceph/msgpool.c

@@ -166,6 +166,10 @@ void ceph_msgpool_put(struct ceph_msgpool *pool, struct ceph_msg *msg)
 {
 	spin_lock(&pool->lock);
 	if (pool->num < pool->min) {
+		/* reset msg front_len; user may have changed it */
+		msg->front.iov_len = pool->front_len;
+		msg->hdr.front_len = cpu_to_le32(pool->front_len);
+
 		kref_set(&msg->kref, 1);  /* retake a single ref */
 		list_add(&msg->list_head, &pool->msgs);
 		pool->num++;