A quick and dirty patch to add Pref64 RA option to odhcpd (RFC 8781)

pref64.diff

diff --git a/src/router.c b/src/router.c
index 541c023..9ad79d4 100644
--- a/src/router.c
+++ b/src/router.c
@@ -390,6 +390,7 @@ enum {
 	IOV_RA_ROUTES,
 	IOV_RA_DNS,
 	IOV_RA_SEARCH,
+	IOV_RA_PREF64,
 	IOV_RA_ADV_INTERVAL,
 	IOV_RA_TOTAL,
 };
@@ -427,6 +428,13 @@ struct nd_opt_route_info {
 	uint32_t addr[4];
 };
 
+struct nd_opt_pref64_info {
+	uint8_t type;
+	uint8_t len;
+	uint16_t lifetime;
+	uint32_t addr[3];
+};
+
 /* Router Advert server mode */
 static int send_router_advert(struct interface *iface, const struct in6_addr *from)
 {
@@ -437,10 +445,11 @@ static int send_router_advert(struct interface *iface, const struct in6_addr *fr
 	struct nd_opt_dns_server *dns = NULL;
 	struct nd_opt_search_list *search = NULL;
 	struct nd_opt_route_info *routes = NULL;
+	struct nd_opt_pref64_info *pref64 = NULL;
 	struct nd_opt_adv_interval adv_interval;
 	struct iovec iov[IOV_RA_TOTAL];
 	struct sockaddr_in6 dest;
-	size_t dns_sz = 0, search_sz = 0, pfxs_cnt = 0, routes_cnt = 0;
+	size_t dns_sz = 0, search_sz = 0, pfxs_cnt = 0, routes_cnt = 0, pref64_sz = 0;
 	ssize_t addr_cnt = 0;
 	uint32_t minvalid = UINT32_MAX, maxival, lifetime;
 	int msecs, mtu = iface->ra_mtu, hlim = iface->ra_hoplimit;
@@ -657,6 +666,17 @@ static int send_router_advert(struct interface *iface, const struct in6_addr *fr
 	iov[IOV_RA_SEARCH].iov_base = (char *)search;
 	iov[IOV_RA_SEARCH].iov_len = search_sz;
 
+	if (1) {
+		pref64_sz = sizeof(*pref64);
+		pref64 = alloca(pref64_sz);
+		memset(pref64, 0, pref64_sz);
+		pref64->type = 38;
+		pref64->len = 2;
+		pref64->lifetime = htons(0xfff8 & (lifetime < UINT16_MAX ? lifetime : UINT16_MAX));
+		pref64->addr[0] = htonl(0x0064ff9b);
+	}
+	iov[IOV_RA_PREF64].iov_base = (char *)pref64;
+	iov[IOV_RA_PREF64].iov_len = pref64_sz;
 	/*
 	 * RFC7084 § 4.3 :
 	 *    L-3:   An IPv6 CE router MUST advertise itself as a router for the
-- 
2.35.1