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>

5 files changed, 41 insertions, 2 deletions

diff --git a/bfdd/bfd.c b/bfdd/bfd.c
index a2e84e928..d4e283483 100644
--- a/bfdd/bfd.c
+++ b/bfdd/bfd.c
@@ -600,6 +600,17 @@ skip_echo:
 		bfd_recvtimer_update(bs);
 		bfd_xmttimer_update(bs, bs->xmt_TO);
 	}
+	if (bpc->bpc_cbit) {
+		if (BFD_CHECK_FLAG(bs->flags, BFD_SESS_FLAG_CBIT))
+			return;
+
+		BFD_SET_FLAG(bs->flags, BFD_SESS_FLAG_CBIT);
+	} else {
+		if (!BFD_CHECK_FLAG(bs->flags, BFD_SESS_FLAG_CBIT))
+			return;
+
+		BFD_UNSET_FLAG(bs->flags, BFD_SESS_FLAG_CBIT);
+	}
 }
 
 static int bfd_session_update(struct bfd_session *bs, struct bfd_peer_cfg *bpc)
diff --git a/bfdd/bfd.h b/bfdd/bfd.h
index 3f3d60383..213e905bf 100644
--- a/bfdd/bfd.h
+++ b/bfdd/bfd.h
@@ -129,6 +129,12 @@ struct bfd_echo_pkt {
 			flags |= (val & 0x3) << 6;                             \
 	}
 #define BFD_GETSTATE(flags) ((flags >> 6) & 0x3)
+#define BFD_SETCBIT(flags, val)                                                \
+	{                                                                      \
+		if ((val))                                                     \
+			flags |= val;                                          \
+	}
+#define BFD_GETCBIT(flags) (flags & BFD_FBIT)
 #define BFD_ECHO_VERSION 1
 #define BFD_ECHO_PKT_LEN sizeof(struct bfd_echo_pkt)
 
@@ -168,6 +174,7 @@ enum bfd_session_flags {
 						 */
 	BFD_SESS_FLAG_SHUTDOWN = 1 << 7,	/* disable BGP peer function */
 	BFD_SESS_FLAG_CONFIG = 1 << 8,	/* Session configured with bfd NB API */
+	BFD_SESS_FLAG_CBIT = 1 << 9,	/* CBIT is set */
 };
 
 #define BFD_SET_FLAG(field, flag) (field |= flag)
@@ -210,6 +217,7 @@ struct bfd_session {
 	uint8_t detect_mult;
 	uint8_t remote_detect_mult;
 	uint8_t mh_ttl;
+	uint8_t remote_cbit;
 
 	/* Timers */
 	struct bfd_timers timers;
diff --git a/bfdd/bfd_packet.c b/bfdd/bfd_packet.c
index 8edba05d1..f3acfa416 100644
--- a/bfdd/bfd_packet.c
+++ b/bfdd/bfd_packet.c
@@ -221,6 +221,10 @@ void ptm_bfd_snd(struct bfd_session *bfd, int fbit)
 	BFD_SETVER(cp.diag, BFD_VERSION);
 	cp.flags = 0;
 	BFD_SETSTATE(cp.flags, bfd->ses_state);
+
+	if (BFD_CHECK_FLAG(bfd->flags, BFD_SESS_FLAG_CBIT))
+		BFD_SETCBIT(cp.flags, BFD_CBIT);
+
 	BFD_SETDEMANDBIT(cp.flags, BFD_DEF_DEMAND);
 
 	/*
@@ -646,6 +650,11 @@ int bfd_recv_cb(struct thread *t)
 		ntohl(cp->timers.required_min_echo);
 	bfd->remote_detect_mult = cp->detect_mult;
 
+	if (BFD_GETCBIT(cp->flags))
+		bfd->remote_cbit = 1;
+	else
+		bfd->remote_cbit = 0;
+
 	/* State switch from section 6.2. */
 	bs_state_handler(bfd, BFD_GETSTATE(cp->flags));
 
diff --git a/bfdd/bfdctl.h b/bfdd/bfdctl.h
index 0da1ca8df..4ce23a8f2 100644
--- a/bfdd/bfdctl.h
+++ b/bfdd/bfdctl.h
@@ -88,6 +88,8 @@ struct bfd_peer_cfg {
 	bool bpc_createonly;
 	bool bpc_shutdown;
 
+	bool bpc_cbit;
+
 	/* Status information */
 	enum bfd_peer_status bpc_bps;
 	uint32_t bpc_id;
diff --git a/bfdd/ptm_adapter.c b/bfdd/ptm_adapter.c
index a12a3c196..3e2ace6ea 100644
--- a/bfdd/ptm_adapter.c
+++ b/bfdd/ptm_adapter.c
@@ -89,6 +89,7 @@ static void debug_printbpc(const char *func, unsigned int line,
 {
 	char addr[3][128];
 	char timers[3][128];
+	char cbit_str[10];
 
 	addr[0][0] = addr[1][0] = addr[2][0] = timers[0][0] = timers[1][0] =
 		timers[2][0] = 0;
@@ -117,9 +118,11 @@ static void debug_printbpc(const char *func, unsigned int line,
 		snprintf(timers[2], sizeof(timers[2]), " detect-multiplier:%d",
 			 bpc->bpc_detectmultiplier);
 
-	log_debug("%s:%d: %s %s%s%s%s%s%s", func, line,
+	sprintf(cbit_str, "CB %x", bpc->bpc_cbit);
+
+	log_debug("%s:%d: %s %s%s%s%s%s%s %s", func, line,
 		  bpc->bpc_mhop ? "multi-hop" : "single-hop", addr[0], addr[1],
-		  addr[2], timers[0], timers[1], timers[2]);
+		  addr[2], timers[0], timers[1], timers[2], cbit_str);
 }
 
 #define DEBUG_PRINTBPC(bpc) debug_printbpc(__FILE__, __LINE__, (bpc))
@@ -173,6 +176,7 @@ int ptm_bfd_notify(struct bfd_session *bs)
 	 *   - AF_INET6:
 	 *     - 16 bytes: ipv6
 	 *   - c: prefix length
+	 * - c: cbit
 	 *
 	 * Commands: ZEBRA_BFD_DEST_REPLAY
 	 *
@@ -219,6 +223,8 @@ int ptm_bfd_notify(struct bfd_session *bs)
 	/* BFD source prefix information. */
 	_ptm_msg_address(msg, bs->key.family, &bs->key.local);
 
+	stream_putc(msg, bs->remote_cbit);
+
 	/* Write packet size. */
 	stream_putw_at(msg, 0, stream_get_endp(msg));
 
@@ -293,6 +299,7 @@ static int _ptm_msg_read(struct stream *msg, int command, vrf_id_t vrf_id,
 	 *       - 16 bytes: ipv6 address
 	 *     - c: ifname length
 	 *     - X bytes: interface name
+	 * - c: bfd_cbit
 	 *
 	 * q(64), l(32), w(16), c(8)
 	 */
@@ -371,6 +378,8 @@ static int _ptm_msg_read(struct stream *msg, int command, vrf_id_t vrf_id,
 		}
 	}
 
+	STREAM_GETC(msg, bpc->bpc_cbit);
+
 	/* Sanity check: peer and local address must match IP types. */
 	if (bpc->bpc_local.sa_sin.sin_family != 0
 	    && (bpc->bpc_local.sa_sin.sin_family