From: John Crispin <john@phrozen.org>
Date: Wed, 17 Jun 2026 08:44:57 +0000 (+0200)
Subject: netifd: dhcp: add restart command for clean lease re-acquire
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=b8175a021b6029f2b1aaf3d766cd645c5c47a8ff;p=thirdparty%2Fopenwrt.git

netifd: dhcp: add restart command for clean lease re-acquire

Add a proto_dhcp_restart() handler that re-acquires the DHCP lease via a
single ubus call, releasing the previous lease and triggering a fresh
DHCPDISCOVER without bouncing the interface.

The re-acquire is implemented by sending SIGHUP to udhcpc, which releases
the current lease (if any) and immediately transitions the state machine
to INIT_SELECTING so the next main-loop iteration sends a fresh
DHCPDISCOVER. A single signal thus expresses 'release this lease and get
a new one' without exiting the client, so upstream watchdogs (e.g. a
DNS-health monitor) can request a clean re-lease without tearing down the
interface.

Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
---

diff --git a/package/network/config/netifd/files/lib/netifd/proto/dhcp.sh b/package/network/config/netifd/files/lib/netifd/proto/dhcp.sh
index 2214fc0b8da..5d8e0dda5e3 100755
--- a/package/network/config/netifd/files/lib/netifd/proto/dhcp.sh
+++ b/package/network/config/netifd/files/lib/netifd/proto/dhcp.sh
@@ -10,6 +10,7 @@ init_proto "$@"
 
 proto_dhcp_init_config() {
 	renew_handler=1
+	restart_handler=1
 
 	proto_config_add_string 'ipaddr:ipaddr'
 	proto_config_add_string 'hostname:hostname'
@@ -115,6 +116,15 @@ proto_dhcp_renew() {
 	[ -n "$sigusr1" ] && proto_kill_command "$interface" $sigusr1
 }
 
+proto_dhcp_restart() {
+	local interface="$1"
+	# SIGHUP asks a patched udhcpc to release the current lease and
+	# immediately re-enter INIT_SELECTING so a fresh DHCPDISCOVER goes
+	# out. Requires the matching busybox udhcpc patch.
+	local sighup="$(kill -l SIGHUP)"
+	[ -n "$sighup" ] && proto_kill_command "$interface" $sighup
+}
+
 proto_dhcp_teardown() {
 	local interface="$1"
 	proto_kill_command "$interface"
diff --git a/package/utils/busybox/patches/700-udhcpc-sighup-restart.patch b/package/utils/busybox/patches/700-udhcpc-sighup-restart.patch
new file mode 100644
index 00000000000..b58d54b6160
--- /dev/null
+++ b/package/utils/busybox/patches/700-udhcpc-sighup-restart.patch
@@ -0,0 +1,48 @@
+From: John Crispin <john@phrozen.org>
+Date: Wed, 15 Apr 2026 16:15:38 +0200
+Subject: [PATCH] udhcpc: treat SIGHUP as release + rediscover
+
+Add a SIGHUP handler to udhcpc that releases the current lease (if any)
+and immediately transitions the state machine to INIT_SELECTING so the
+next main-loop iteration sends a fresh DHCPDISCOVER. This lets a single
+signal express 'release this lease and get a new one' without exiting
+the client, so upstream watchdogs (e.g. a DNS-health monitor) can
+request a clean re-lease without tearing down the interface.
+
+Signed-off-by: John Crispin <john@phrozen.org>
+---
+--- a/networking/udhcp/dhcpc.c
++++ b/networking/udhcp/dhcpc.c
+@@ -1606,6 +1606,22 @@ int udhcpc_main(int argc UNUSED_PARAM, c
+ 			/* ^^^ switches to LISTEN_NONE */
+ 			timeout = INT_MAX;
+ 			continue;
++		case SIGHUP:
++			bb_info_msg("received SIGHUP, restarting DHCP session");
++			/* release the current lease if we have one */
++			if (client_data.state != INIT_SELECTING
++			 && client_data.state != RELEASED)
++				perform_release(server_id, requested_ip);
++			/* drop any cached offer, kick the state machine into
++			 * INIT_SELECTING so the next iteration sends a fresh
++			 * DHCPDISCOVER */
++			change_listen_mode(LISTEN_NONE);
++			server_id = 0;
++			requested_ip = 0;
++			packet_num = 0;
++			client_data.state = INIT_SELECTING;
++			timeout = 0;
++			continue;
+ 		case SIGTERM:
+ 			bb_info_msg("received %s", "SIGTERM");
+ 			goto ret0;
+--- a/networking/udhcp/signalpipe.c
++++ b/networking/udhcp/signalpipe.c
+@@ -58,6 +58,7 @@ void FAST_FUNC udhcp_sp_setup(void)
+ 	bb_signals(0
+ 		+ (1 << SIGUSR1)
+ 		+ (1 << SIGUSR2)
++		+ (1 << SIGHUP)
+ 		+ (1 << SIGTERM)
+ 		, signal_handler);
+ }