bfdd, lib, bgpd: add bfd cbit usage

bfd cbit is a value carried out in bfd messages, that permit to keep or
not, the independence between control plane and dataplane. In other
words, while most of the cases plan to flush entries, when bfd goes
down, there are some cases where that bfd event should be ignored. this
is the case with non stop forwarding mechanisms where entries may be
kept. this is the case for BGP, when graceful restart capability is
used. If BFD event down happens, and bgp is in graceful restart mode, it
is wished to ignore the BFD event while waiting for the remote router to
restart.
The changes take into account the following:
- add a config flag across zebra layer so that daemon can set or not the
  cbit capability.
- ability for daemons to read the remote bfd capability associated to a bfd
  notification.
- in bfdd, according to the value, the cbit value is set
- in bfdd, the received value is retrived and stored in the bfd session
  context.
- by default, the local cbit announced to remote is set to 1 while
  preservation of the local path is not set.

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/lib/bfd.h b/lib/bfd.h
index d02110a997..7f376a2470 100644
--- a/lib/bfd.h
+++ b/lib/bfd.h
@@ -48,6 +48,7 @@ struct bfd_gbl {
 #define BFD_FLAG_PARAM_CFG (1 << 0) /* parameters have been configured */
 #define BFD_FLAG_BFD_REG   (1 << 1) /* Peer registered with BFD */
 #define BFD_FLAG_BFD_TYPE_MULTIHOP (1 << 2) /* Peer registered with BFD as multihop */
+#define BFD_FLAG_BFD_CBIT_ON (1 << 3) /* Peer registered with CBIT set to on */
 
 #define BFD_STATUS_UNKNOWN (1 << 0) /* BFD session status never received */
 #define BFD_STATUS_DOWN    (1 << 1) /* BFD session status is down */
@@ -83,13 +84,14 @@ extern void bfd_set_param(struct bfd_info **bfd_info, uint32_t min_rx,
 			  int *command);
 extern void bfd_peer_sendmsg(struct zclient *zclient, struct bfd_info *bfd_info,
 			     int family, void *dst_ip, void *src_ip,
-			     char *if_name, int ttl, int multihop, int command,
-			     int set_flag, vrf_id_t vrf_id);
+			     char *if_name, int ttl, int multihop, int cbit,
+			     int command, int set_flag, vrf_id_t vrf_id);
 
 extern const char *bfd_get_command_dbg_str(int command);
 
 extern struct interface *bfd_get_peer_info(struct stream *s, struct prefix *dp,
 					   struct prefix *sp, int *status,
+					   int *remote_cbit,
 					   vrf_id_t vrf_id);
 
 const char *bfd_get_status_str(int status);