Add ia_pd_suffix option

First pass of adding an option to allow customization of the suffix used on an
address when configuring a new delegated prefix.

dhcpcd.conf.5.in

@@ -229,6 +229,17 @@ IPv6RS should be disabled globally when requesting a Prefix Delegation like so:
 .Pp
 .D1 interface eth0
 .D1 ia_pd 1 eth1/0 eth2/1
+.It Ic ia_pd_suffix Ar address Ns
+The second half of
+.Ar address
+will be used as the IPv6 suffix for any delegations.
+Defaults to the suffix of the link-local address on the interface.
+Can be set globally or per interface.
+Example:
+.Pp
+.D1 ia_pd_suffix ::1
+.D1 interface eth0
+.D1 ia_pd_suffix ::cafe:babe
 .It Ic ipv4only
 Only configure IPv4.
 .It Ic ipv6only

if-options.c

@@ -73,6 +73,7 @@ unsigned long long options = 0;
 #define O_NOIPV4		O_BASE + 16
 #define O_NOIPV6		O_BASE + 17
 #define O_IAID			O_BASE + 18
+#define O_IA_PD_SUFFIX		O_BASE + 19
 
 char *dev_load;
 
@@ -142,6 +143,7 @@ const struct option cf_options[] = {
 	{"hostname_short",  no_argument,       NULL, O_HOSTNAME_SHORT},
 	{"dev",             required_argument, NULL, O_DEV},
 	{"nodev",           no_argument,       NULL, O_NODEV},
+	{"ia_pd_suffix",    required_argument, NULL, O_IA_PD_SUFFIX},
 	{NULL,              0,                 NULL, '\0'}
 };
 
@@ -1122,8 +1124,19 @@ parse_option(struct if_options *ifo, int opt, const char *arg)
 				}
 			}
 		}
-#endif
 		break;
+	case O_IA_PD_SUFFIX:
+		free(ifo->ia_suffix);
+		ifo->ia_suffix = malloc(sizeof(*ifo->ia_suffix));
+		if (inet_pton(AF_INET6, arg, ifo->ia_suffix) != 1) {
+			syslog(LOG_WARNING, "%s is not a valid IPv6 address",
+				arg);
+			free(ifo->ia_suffix);
+			ifo->ia_suffix = NULL;
+			return -1;
+		}
+		break;
+#endif
 	case O_HOSTNAME_SHORT:
 		ifo->options |= DHCPCD_HOSTNAME | DHCPCD_HOSTNAME_SHORT;
 		break;
@@ -1321,6 +1334,8 @@ free_options(struct if_options *ifo)
 #ifdef INET6
 		for (i = 0; i < ifo->ia_len; i++)
 			free(ifo->ia[i].sla);
+
+		free(ifo->ia_suffix);
 #endif
 		free(ifo->ia);
 

if-options.h

@@ -157,6 +157,7 @@ struct if_options {
 	uint16_t ia_type;
 	struct if_ia *ia;
 	size_t ia_len;
+	struct in6_addr *ia_suffix;
 #ifdef INET6
 	int dadtransmits;
 #endif

ipv6.c

@@ -154,12 +154,19 @@ ipv6_makeaddr(struct in6_addr *addr, const struct interface *ifp,
 
 	memcpy(addr, prefix, sizeof(*prefix));
 
-	/* Try and make the address from the first local-link address */
-	ap = ipv6_linklocal(ifp);
-	if (ap) {
-		addr->s6_addr32[2] = ap->addr.s6_addr32[2];
-		addr->s6_addr32[3] = ap->addr.s6_addr32[3];
+	/* Use the user-provided suffix, otherwise try and make the address
+	 * from the first local-link address */
+	if(ifp->options->ia_suffix) {
+		addr->s6_addr32[2] = ifp->options->ia_suffix->s6_addr32[2];
+		addr->s6_addr32[3] = ifp->options->ia_suffix->s6_addr32[3];
 		return 0;
+	} else {
+		ap = ipv6_linklocal(ifp);
+		if (ap) {
+			addr->s6_addr32[2] = ap->addr.s6_addr32[2];
+			addr->s6_addr32[3] = ap->addr.s6_addr32[3];
+			return 0;
+		}
 	}
 
 	/* Because we delay a few functions until we get a local-link address