ndp: Don't send first periodic router advertisement right after guest connects

This is very visible with muvm, but it also happens with QEMU: we're
sending the first unsolicited router advertisement milliseconds after
the guest connects.

That's usually pointless because, when the hypervisor connects, the
guest is typically not ready yet to process anything of that sort:
it's still booting. And if we happen to send it late enough (still
milliseconds), with muvm, while the message is discarded, it
sometimes (slightly) delays the response to the first solicited
router advertisement, which is the one we need to have coming fast.

Skip sending the unsolicited advertisement on the first timer run,
just calculate the next delay. Keep it simple by observing that we're
probably not trying to reach the 1970s with IPv6.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 4 insertions, 0 deletions

diff --git a/ndp.c b/ndp.c
index 1752d64..37bf7a3 100644
--- a/ndp.c
+++ b/ndp.c
@@ -420,9 +420,13 @@ void ndp_timer(const struct ctx *c, const struct timespec *now)
 	interval = min_rtr_adv_interval +
 		random() % (max_rtr_adv_interval - min_rtr_adv_interval);
 
+	if (!next_ra)
+		goto first;
+
 	info("NDP: sending unsolicited RA, next in %llds", (long long)interval);
 
 	ndp_ra(c, &in6addr_ll_all_nodes);
 
+first:
 	next_ra = now->tv_sec + interval;
 }