bgpd: introduce new alloc algorithm for SRv6 SID

Current implementation of SRv6 SID allocation algorithm sets most least
2 bytes. But, according to RFC8986, function bits is located in the next
to locator. New allocation alogirithm respects this format.

Signed-off-by: Ryoga Saito <contact@proelbtn.com>

bgpd/bgp_mplsvpn.c

@@ -522,31 +522,32 @@ static bool sid_exist(struct bgp *bgp, const struct in6_addr *sid)
  * if index != 0: try to allocate as index-mode
  * else: try to allocate as auto-mode
  */
-static bool alloc_new_sid(struct bgp *bgp, uint32_t index,
-			  struct in6_addr *sid)
+static uint32_t alloc_new_sid(struct bgp *bgp, uint32_t index,
+			      struct in6_addr *sid)
 {
 	struct listnode *node;
 	struct prefix_ipv6 *chunk;
 	struct in6_addr sid_buf;
 	bool alloced = false;
+	int label;
 
 	if (!bgp || !sid)
 		return false;
 
 	for (ALL_LIST_ELEMENTS_RO(bgp->srv6_locator_chunks, node, chunk)) {
 		sid_buf = chunk->prefix;
 		if (index != 0) {
-			sid_buf.s6_addr[15] = index;
+			label = index << 12;
+			transpose_sid(&sid_buf, label, 64, 16);
 			if (sid_exist(bgp, &sid_buf))
 				return false;
 			alloced = true;
 			break;
 		}
 
 		for (size_t i = 1; i < 255; i++) {
-			sid_buf.s6_addr[15] = (i & 0xff00) >> 8;
-			sid_buf.s6_addr[14] = (i & 0x00ff);
-
+			label = i << 12;
+			transpose_sid(&sid_buf, label, 64, 16);
 			if (sid_exist(bgp, &sid_buf))
 				continue;
 			alloced = true;
@@ -555,20 +556,19 @@ static bool alloc_new_sid(struct bgp *bgp, uint32_t index,
 	}
 
 	if (!alloced)
-		return false;
+		return 0;
 
 	sid_register(bgp, &sid_buf, bgp->srv6_locator_name);
 	*sid = sid_buf;
-	return true;
+	return label;
 }
 
 void ensure_vrf_tovpn_sid(struct bgp *bgp_vpn, struct bgp *bgp_vrf, afi_t afi)
 {
 	int debug = BGP_DEBUG(vpn, VPN_LEAK_FROM_VRF);
-	bool alloced = false;
 	char buf[256];
 	struct in6_addr *sid;
-	uint32_t tovpn_sid_index = 0;
+	uint32_t tovpn_sid_index = 0, tovpn_sid_transpose_label;
 	bool tovpn_sid_auto = false;
 
 	if (debug)
@@ -602,8 +602,9 @@ void ensure_vrf_tovpn_sid(struct bgp *bgp_vpn, struct bgp *bgp_vrf, afi_t afi)
 	}
 
 	sid = XCALLOC(MTYPE_BGP_SRV6_SID, sizeof(struct in6_addr));
-	alloced = alloc_new_sid(bgp_vpn, tovpn_sid_index, sid);
-	if (!alloced) {
+	tovpn_sid_transpose_label =
+		alloc_new_sid(bgp_vpn, tovpn_sid_index, sid);
+	if (tovpn_sid_transpose_label == 0) {
 		zlog_debug("%s: not allocated new sid for vrf %s: afi %s",
 			   __func__, bgp_vrf->name_pretty, afi2str(afi));
 		return;
@@ -615,9 +616,22 @@ void ensure_vrf_tovpn_sid(struct bgp *bgp_vpn, struct bgp *bgp_vrf, afi_t afi)
 			   __func__, buf, bgp_vrf->name_pretty,
 			   afi2str(afi));
 	}
+	bgp_vrf->vpn_policy[afi].tovpn_sid_transpose_label =
+		tovpn_sid_transpose_label;
 	bgp_vrf->vpn_policy[afi].tovpn_sid = sid;
 }
 
+void transpose_sid(struct in6_addr *sid, uint32_t label, uint8_t offset,
+		   uint8_t len)
+{
+	for (uint8_t idx = 0; idx < len; idx++) {
+		uint8_t tidx = offset + idx;
+		sid->s6_addr[tidx / 8] &= ~(0x1 << (7 - tidx % 8));
+		if (label >> (19 - idx) & 0x1)
+			sid->s6_addr[tidx / 8] |= 0x1 << (7 - tidx % 8);
+	}
+}
+
 static bool ecom_intersect(struct ecommunity *e1, struct ecommunity *e2)
 {
 	uint32_t i, j;

bgpd/bgp_mplsvpn.h

@@ -81,6 +81,8 @@ extern void vpn_leak_zebra_vrf_sid_update(struct bgp *bgp, afi_t afi);
 extern void vpn_leak_zebra_vrf_sid_withdraw(struct bgp *bgp, afi_t afi);
 extern int vpn_leak_label_callback(mpls_label_t label, void *lblid, bool alloc);
 extern void ensure_vrf_tovpn_sid(struct bgp *vpn, struct bgp *vrf, afi_t afi);
+extern void transpose_sid(struct in6_addr *sid, uint32_t label, uint8_t offset,
+			  uint8_t size);
 extern void vrf_import_from_vrf(struct bgp *to_bgp, struct bgp *from_bgp,
 				afi_t afi, safi_t safi);
 void vrf_unimport_from_vrf(struct bgp *to_bgp, struct bgp *from_bgp,

bgpd/bgpd.h

@@ -241,6 +241,7 @@ struct vpn_policy {
 	 */
 	uint32_t tovpn_sid_index; /* unset => set to 0 */
 	struct in6_addr *tovpn_sid;
+	uint32_t tovpn_sid_transpose_label;
 	struct in6_addr *tovpn_zebra_vrf_sid_last_sent;
 };