ospfd: add support for unplanned graceful restart

In practical terms, unplanned GR refers to the act of recovering
from a software crash without affecting the forwarding plane.

Unplanned GR and Planned GR work virtually the same, except for the
following difference: on planned GR, the router sends the Grace-LSAs
*before* restarting, whereas in unplanned GR the router sends the
Grace-LSAs immediately *after* restarting.

For unplanned GR to work, ospf6d was modified to send a
ZEBRA_CLIENT_GR_CAPABILITIES message to zebra as soon as GR is
enabled.  This causes zebra to freeze the OSPF routes in the RIB as
soon as the ospfd daemon dies, for as long as the configured grace
period (the defaults is 120 seconds). Similarly, ospfd now stores in
non-volatile memory that GR is enabled as soon as GR is configured.
Those two things are no longer done during the GR preparation phase,
which only happens for planned GRs.

Unplanned GR will only take effect when the daemon is killed
abruptly (e.g. SIGSEGV, SIGKILL), otherwise all OSPF routes will
be uninstalled while ospfd is exiting.  Once ospfd starts, it will
check whether GR is enabled and enter in the GR mode if necessary,
sending Grace-LSAs out all operational interfaces.

One disadvantage of unplanned GR is that the neighboring routers
might time out their corresponding adjacencies if ospfd takes too
long to come back up. This is especially the case when short dead
intervals are used (or BFD). For this and other reasons, planned
GR should be preferred whenever possible.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>

1 files changed, 2 insertions, 3 deletions

diff --git a/ospfd/ospf_packet.c b/ospfd/ospf_packet.c
index 552acfd6d3..66d3df2f97 100644
--- a/ospfd/ospf_packet.c
+++ b/ospfd/ospf_packet.c
@@ -4040,9 +4040,8 @@ static struct ospf_packet *ospf_ls_upd_packet_new(struct list *update,
 	return ospf_packet_new(size - sizeof(struct ip));
 }
 
-static void ospf_ls_upd_queue_send(struct ospf_interface *oi,
-				   struct list *update, struct in_addr addr,
-				   int send_lsupd_now)
+void ospf_ls_upd_queue_send(struct ospf_interface *oi, struct list *update,
+			    struct in_addr addr, int send_lsupd_now)
 {
 	struct ospf_packet *op;
 	uint16_t length = OSPF_HEADER_SIZE;