bgpd: transfer packets from peer stub to actual peer

During transition from OpenConfirm -> Established, we wipe the peer stub's
output buffer. Because thread.c prioritizes I/O operations over regular
background threads and events, in a single threaded environment this ordering
meant that the output buffer would be happily empty at wipe time.  In MT-land,
this convenient coincidence is no longer true; thus we need to make sure that
any packets remaining on the peer stub get transferred over to the peer proper.

Also removes misleading comment indicating that bgp_establish() sends a
keepalive packet. It does not.

Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>

diff --git a/bgpd/bgp_fsm.c b/bgpd/bgp_fsm.c
index aa883f73645d69ccd6123c4085164404de6a5cf1..3344bf3126661016be61a93e8b18d8e95a3b6299 100644 (file)
--- a/bgpd/bgp_fsm.c
+++ b/bgpd/bgp_fsm.c
@@ -138,17 +138,22 @@ static struct peer *peer_xfer_conn(struct peer *from_peer)
        from_peer->fd = fd;
        stream_reset(peer->ibuf);
 
+       // At this point in time, it is possible that there are packets pending
+       // on
+       // from_peer->obuf. These need to be transferred to the new peer struct.
        pthread_mutex_lock(&peer->obuf_mtx);
+       pthread_mutex_lock(&from_peer->obuf_mtx);
        {
+               // wipe new peer's packet queue
                stream_fifo_clean(peer->obuf);
-       }
-       pthread_mutex_unlock(&peer->obuf_mtx);
 
-       pthread_mutex_lock(&from_peer->obuf_mtx);
-       {
-               stream_fifo_clean(from_peer->obuf);
+               // copy each packet from old peer's queue to new peer's queue
+               while (from_peer->obuf->head)
+                       stream_fifo_push(peer->obuf,
+                                        stream_fifo_pop(from_peer->obuf));
        }
        pthread_mutex_unlock(&from_peer->obuf_mtx);
+       pthread_mutex_unlock(&peer->obuf_mtx);
 
        peer->as = from_peer->as;
        peer->v_holdtime = from_peer->v_holdtime;
@@ -1398,8 +1403,12 @@ static int bgp_fsm_holdtime_expire(struct peer *peer)
        return bgp_stop_with_notify(peer, BGP_NOTIFY_HOLD_ERR, 0);
 }
 
-/* Status goes to Established.  Send keepalive packet then make first
-   update information. */
+/**
+ * Transition to Established state.
+ *
+ * Convert peer from stub to full fledged peer, set some timers, and generate
+ * initial updates.
+ */
 static int bgp_establish(struct peer *peer)
 {
        afi_t afi;