When activating an interface, bring up a basic config that does nothing.

Then apply enough of the config for the base protocol, passed via an
argument, to work.

This means that when a prefix is delegated to an inactive interface, it
won't magically start configuring IPv4 on it.

dhcp6.c

@@ -3047,7 +3047,6 @@ recv:
 
 		ipv6nd_runignoredra(ifp);
 		ipv6_addaddrs(&state->addrs);
-		dhcp6_delegate_prefix(ifp);
 
 		if (state->state == DH6S_INFORMED)
 			logger(ifp->ctx, has_new ? LOG_INFO : LOG_DEBUG,
@@ -3064,6 +3063,7 @@ recv:
 		if_initrt6(ifp);
 		ipv6_buildroutes(ifp->ctx);
 		dhcp6_writelease(ifp);
+		dhcp6_delegate_prefix(ifp);
 		dhcp6_script_try_run(ifp, 0);
 	}
 
@@ -3188,7 +3188,8 @@ dhcp6_start1(void *arg)
 				logger(ifp->ctx, LOG_INFO,
 				    "%s: activating for delegation",
 				    sla->ifname);
-				dhcpcd_activateinterface(ifd);
+				dhcpcd_activateinterface(ifd,
+				    DHCPCD_IPV6 | DHCPCD_DHCP6);
 			}
 		}
 	}

dhcpcd.c

@@ -671,13 +671,21 @@ dhcpcd_pollup(void *arg)
 }
 
 static void
-dhcpcd_initstate1(struct interface *ifp, int argc, char **argv,
-    unsigned long long options)
+dhcpcd_initstate2(struct interface *ifp, unsigned long long options)
 {
 	struct if_options *ifo;
 
-	configure_interface(ifp, argc, argv, options);
-	ifo = ifp->options;
+	if (options) {
+		if ((ifo = default_config(ifp->ctx)) == NULL) {
+			logger(ifp->ctx, LOG_ERR, "%s: %s: %m",
+			    ifp->name, __func__);
+			return;
+		}
+		ifo->options |= options;
+		free(ifp->options);
+		ifp->options = ifo;
+	} else
+		ifo = ifp->options;
 
 	if (ifo->options & DHCPCD_IPV4 && ipv4_init(ifp->ctx) == -1) {
 		logger(ifp->ctx, LOG_ERR, "ipv4_init: %m");
@@ -698,6 +706,15 @@ dhcpcd_initstate1(struct interface *ifp, int argc, char **argv,
 	}
 }
 
+static void
+dhcpcd_initstate1(struct interface *ifp, int argc, char **argv,
+    unsigned long long options)
+{
+
+	configure_interface(ifp, argc, argv, options);
+	dhcpcd_initstate2(ifp, 0);
+}
+
 static void
 dhcpcd_initstate(struct interface *ifp, unsigned long long options)
 {
@@ -999,12 +1016,13 @@ run_preinit(struct interface *ifp)
 }
 
 void
-dhcpcd_activateinterface(struct interface *ifp)
+dhcpcd_activateinterface(struct interface *ifp, unsigned long long options)
 {
 
 	if (!ifp->active) {
 		ifp->active = IF_ACTIVE;
-		dhcpcd_initstate(ifp, 0);
+		dhcpcd_initstate2(ifp, options);
+		configure_interface1(ifp);
 		run_preinit(ifp);
 		dhcpcd_prestartinterface(ifp);
 	}

dhcpcd.h

@@ -206,6 +206,6 @@ void dhcpcd_dropinterface(struct interface *, const char *);
 int dhcpcd_selectprofile(struct interface *, const char *);
 
 void dhcpcd_startinterface(void *);
-void dhcpcd_activateinterface(struct interface *);
+void dhcpcd_activateinterface(struct interface *, unsigned long long);
 
 #endif

if-options.c

@@ -2140,6 +2140,32 @@ get_line(char ** __restrict buf, size_t * __restrict buflen,
 	return p;
 }
 
+struct if_options *
+default_config(struct dhcpcd_ctx *ctx)
+{
+	struct if_options *ifo;
+
+	/* Seed our default options */
+	if ((ifo = calloc(1, sizeof(*ifo))) == NULL) {
+		logger(ctx, LOG_ERR, "%s: %m", __func__);
+		return NULL;
+	}
+	ifo->options |= DHCPCD_IF_UP | DHCPCD_LINK | DHCPCD_INITIAL_DELAY;
+	ifo->timeout = DEFAULT_TIMEOUT;
+	ifo->reboot = DEFAULT_REBOOT;
+	ifo->metric = -1;
+	ifo->auth.options |= DHCPCD_AUTH_REQUIRE;
+	TAILQ_INIT(&ifo->auth.tokens);
+
+	/* Inherit some global defaults */
+	if (ctx->options & DHCPCD_PERSISTENT)
+		ifo->options |= DHCPCD_PERSISTENT;
+	if (ctx->options & DHCPCD_SLAACPRIVATE)
+		ifo->options |= DHCPCD_SLAACPRIVATE;
+
+	return ifo;
+}
+
 struct if_options *
 read_config(struct dhcpcd_ctx *ctx,
     const char *ifname, const char *ssid, const char *profile)
@@ -2162,13 +2188,9 @@ read_config(struct dhcpcd_ctx *ctx,
 	struct dhcp_opt *ldop, *edop;
 
 	/* Seed our default options */
-	ifo = calloc(1, sizeof(*ifo));
-	if (ifo == NULL) {
-		logger(ctx, LOG_ERR, "%s: %m", __func__);
+	if ((ifo = default_config(ctx)) == NULL)
 		return NULL;
-	}
-	ifo->options |= DHCPCD_DAEMONISE | DHCPCD_LINK | DHCPCD_INITIAL_DELAY;
-	ifo->options |= DHCPCD_IF_UP;
+	ifo->options |= DHCPCD_DAEMONISE;
 #ifdef PLUGIN_DEV
 	ifo->options |= DHCPCD_DEV;
 #endif
@@ -2181,11 +2203,6 @@ read_config(struct dhcpcd_ctx *ctx,
 	ifo->options |= DHCPCD_IPV6RA_AUTOCONF | DHCPCD_IPV6RA_REQRDNSS;
 	ifo->options |= DHCPCD_DHCP6;
 #endif
-	ifo->timeout = DEFAULT_TIMEOUT;
-	ifo->reboot = DEFAULT_REBOOT;
-	ifo->metric = -1;
-	ifo->auth.options |= DHCPCD_AUTH_REQUIRE;
-	TAILQ_INIT(&ifo->auth.tokens);
 
 	vlen = dhcp_vendor((char *)ifo->vendorclassid + 1,
 	            sizeof(ifo->vendorclassid) - 1);

if-options.h

@@ -215,6 +215,7 @@ struct if_options {
 	struct auth auth;
 };
 
+struct if_options *default_config(struct dhcpcd_ctx *);
 struct if_options *read_config(struct dhcpcd_ctx *,
     const char *, const char *, const char *);
 int add_options(struct dhcpcd_ctx *, const char *,