change dhcpd to use the rdomain/rtable it was started in.

previously it would use the rdomain on the first interface it was
explicitly configured to open. it is much more natural to use the rdomain it's been started in, which integrates better with rcctl.

a version of this was tested by mark patruck
ok kn@ claudio@

usr.sbin/dhcpd/dhcpd.c

···
-/*	$OpenBSD: dhcpd.c,v 1.61 2025/06/04 21:16:25 dlg Exp $ */
+/*	$OpenBSD: dhcpd.c,v 1.62 2025/06/10 06:29:53 dlg Exp $ */
 
 /*
  * Copyright (c) 2004 Henning Brauer <[e-mail]>
···
 u_int16_t server_port;
 u_int16_t client_port;
 
+int rdomain;
 struct passwd *pw;
 int log_priority;
 int pfpipe[2];
···
 int
 main(int argc, char *argv[])
 {
-	int ch, cftest = 0, rdomain = -1, udpsockmode = 0;
+	int ch, cftest = 0, udpsockmode = 0;
 	int debug = 0, verbose = 0;
 	char *sync_iface = NULL;
 	char *sync_baddr = NULL;
···
 
 	log_init(1, LOG_DAEMON);	/* log to stderr until daemonized */
 	log_setverbose(1);
+
+	rdomain = getrtable();
 
 	opterr = 0;
 	while ((ch = getopt(argc, argv, "A:C:L:c:dfl:nu::vY:y:")) != -1)
···
 
 	db_startup();
 	if (!udpsockmode || argc > 0)
-		discover_interfaces(&rdomain);
-
-	if (rdomain != -1)
-		if (setrtable(rdomain) == -1)
-			fatal("setrtable");
+		discover_interfaces();
 
 	if (syncsend || syncrecv) {
 		if (sync_init(sync_iface, sync_baddr, sync_port) == -1)

usr.sbin/dhcpd/dhcpd.h

···
-/*	$OpenBSD: dhcpd.h,v 1.72 2025/05/31 07:47:45 dlg Exp $ */
+/*	$OpenBSD: dhcpd.h,v 1.73 2025/06/10 06:29:53 dlg Exp $ */
 
 /*
  * Copyright (c) 1995, 1996, 1997, 1998, 1999
···
 extern struct interface_info *interfaces;
 extern struct protocol *protocols;
 extern struct dhcpd_timeout *timeouts;
-void discover_interfaces(int *);
+void discover_interfaces(void);
 void dispatch(void);
 int locate_network(struct packet *);
 void got_one(struct protocol *);

usr.sbin/dhcpd/dispatch.c

···
-/*	$OpenBSD: dispatch.c,v 1.49 2025/06/04 21:16:25 dlg Exp $ */
+/*	$OpenBSD: dispatch.c,v 1.50 2025/06/10 06:29:53 dlg Exp $ */
 
 /*
  * Copyright (c) 1995, 1996, 1997, 1998, 1999
···
 #include "log.h"
 #include "sync.h"
 
+extern int rdomain;
+
 struct interface_info *interfaces;
 struct protocol *protocols;
 struct dhcpd_timeout *timeouts;
···
    subnet it's on, and add it to the list of interfaces. */
 
 void
-discover_interfaces(int *rdomain)
+discover_interfaces(void)
 {
 	struct interface_info *tmp;
 	struct interface_info *last, *next;
 	struct subnet *subnet;
 	struct shared_network *share;
 	struct sockaddr_in foo;
-	int ir = 0, ird;
+	int ir;
 	struct ifreq *tif;
 	struct ifaddrs *ifap, *ifa;
 
···
 	 * If we already have a list of interfaces, the interfaces were
 	 * requested.
 	 */
-	if (interfaces != NULL)
-		ir = 1;
-	else
-		/* must specify an interface when rdomains are used */
-		*rdomain = 0;
+	ir = (interfaces != NULL);
 
 	/* Cycle through the list of interfaces looking for IP addresses. */
 	for (ifa = ifap; ifa != NULL; ifa = ifa->ifa_next) {
···
 		if (tmp == NULL && ir)
 			continue;
 
-		ird = get_rdomain(ifa->ifa_name);
-		if (*rdomain == -1)
-			*rdomain = ird;
-		else if (*rdomain != ird && ir)
-			fatalx("Interface %s is not in rdomain %d",
-			    tmp->name, *rdomain);
-		else if (*rdomain != ird && !ir)
-			continue;
-
 		/* If there isn't already an interface by this name,
 		   allocate one. */
 		if (tmp == NULL) {
···
 		/* If we have the capability, extract link information
 		   and record it in a linked list. */
 		if (ifa->ifa_addr->sa_family == AF_LINK) {
-			struct sockaddr_dl *sdl =
-			    ((struct sockaddr_dl *)(ifa->ifa_addr));
+			struct if_data *ifi = ifa->ifa_data;
+			struct sockaddr_dl *sdl;
+
+			if (rdomain != ifi->ifi_rdomain)
+				continue;
+
+			sdl = (struct sockaddr_dl *)ifa->ifa_addr;
 			tmp->index = sdl->sdl_index;
 			tmp->hw_address.hlen = sdl->sdl_alen;
 			tmp->hw_address.htype = HTYPE_ETHER; /* XXX */
 			memcpy(tmp->hw_address.haddr,
 			    LLADDR(sdl), sdl->sdl_alen);
 		} else if (ifa->ifa_addr->sa_family == AF_INET) {
-			struct iaddr addr;
-
 			/* Get a pointer to the address... */
 			memcpy(&foo, ifa->ifa_addr, sizeof(foo));
 
···
 				tmp->ifp = tif;
 				tmp->primary_address = foo.sin_addr;
 			}
-
-			/* Grab the address... */
-			addr.len = 4;
-			memcpy(addr.iabuf, &foo.sin_addr.s_addr, addr.len);
-
-			/* If there's a registered subnet for this address,
-			   connect it together... */
-			if ((subnet = find_subnet(addr))) {
-				/* If this interface has multiple aliases
-				   on the same subnet, ignore all but the
-				   first we encounter. */
-				if (!subnet->interface) {
-					subnet->interface = tmp;
-					subnet->interface_address = addr;
-				} else if (subnet->interface != tmp) {
-					log_warnx("Multiple %s %s: %s %s",
-					    "interfaces match the",
-					    "same subnet",
-					    subnet->interface->name,
-					    tmp->name);
-				}
-				share = subnet->shared_network;
-				if (tmp->shared_network &&
-				    tmp->shared_network != share) {
-					log_warnx("Interface %s matches %s",
-					    tmp->name,
-					    "multiple shared networks");
-				} else {
-					tmp->shared_network = share;
-				}
-
-				if (!share->interface) {
-					share->interface = tmp;
-				} else if (share->interface != tmp) {
-					log_warnx("Multiple %s %s: %s %s",
-					    "interfaces match the",
-					    "same shared network",
-					    share->interface->name,
-					    tmp->name);
-				}
-			}
 		}
 	}
 
 	/* Discard interfaces we can't listen on. */
 	last = NULL;
 	for (tmp = interfaces; tmp; tmp = next) {
+		struct iaddr addr;
+
 		next = tmp->next;
 
+		if (tmp->index == 0) {
+			log_warnx("Can't listen on %s - wrong rdomain",
+			    tmp->name);
+			/* Remove tmp from the list of interfaces. */
+			if (!last)
+				interfaces = interfaces->next;
+			else
+				last->next = tmp->next;
+			continue;
+		}
+
 		if (!tmp->ifp) {
 			log_warnx("Can't listen on %s - it has no IP address.",
 			    tmp->name);
···
 		}
 
 		memcpy(&foo, &tmp->ifp->ifr_addr, sizeof tmp->ifp->ifr_addr);
+
+		/* Grab the address... */
+		addr.len = 4;
+		memcpy(addr.iabuf, &foo.sin_addr.s_addr, addr.len);
+
+		/* If there's a registered subnet for this address,
+		   connect it together... */
+		if ((subnet = find_subnet(addr))) {
+			/* If this interface has multiple aliases
+			   on the same subnet, ignore all but the
+			   first we encounter. */
+			if (!subnet->interface) {
+				subnet->interface = tmp;
+				subnet->interface_address = addr;
+			} else if (subnet->interface != tmp) {
+				log_warnx("Multiple %s %s: %s %s",
+				    "interfaces match the",
+				    "same subnet",
+				    subnet->interface->name,
+				    tmp->name);
+			}
+			share = subnet->shared_network;
+			if (tmp->shared_network &&
+			    tmp->shared_network != share) {
+				log_warnx("Interface %s matches %s",
+				    tmp->name,
+				    "multiple shared networks");
+			} else {
+				tmp->shared_network = share;
+			}
+
+			if (!share->interface) {
+				share->interface = tmp;
+			} else if (share->interface != tmp) {
+				log_warnx("Multiple %s %s: %s %s",
+				    "interfaces match the",
+				    "same shared network",
+				    share->interface->name,
+				    tmp->name);
+			}
+		}
 
 		if (!tmp->shared_network) {
 			log_warnx("Can't listen on %s - dhcpd.conf has no "
···
 		}
 	}
 }
-
-int
-get_rdomain(char *name)
-{
-	int rv = 0, s;
-	struct  ifreq ifr;
-
-	if ((s = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
-		fatal("get_rdomain socket");
-
-	memset(&ifr, 0, sizeof(ifr));
-	strlcpy(ifr.ifr_name, name, sizeof(ifr.ifr_name));
-	if (ioctl(s, SIOCGIFRDOMAIN, (caddr_t)&ifr) != -1)
-		rv = ifr.ifr_rdomainid;
-
-	close(s);
-	return rv;
-}