base-files: configure the preinit interface on hotplug

preinit_ip runs once when preinit starts and configures the preinit
interface only if its driver has already registered it. Drivers that
probe while preinit is running leave failsafe without a network.

Run procd's preinit hotplug daemon on net add events, as the rule in
hotplug-preinit.json.d does, and have it start /sbin/preinit-netdev.
The script runs the new preinit_netdev boot hook, which targets use to
rename the new netdev, and then calls preinit_ip_event, which
configures the preinit interface unless it already carries the
preinit address.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

package/base-files/Makefile

@@ -194,6 +194,7 @@ define Package/base-files/install
 
 	$(SED) "s#%PATH%#$(TARGET_INIT_PATH)#g" \
 		$(1)/sbin/hotplug-call \
+		$(1)/sbin/preinit-netdev \
 		$(1)/etc/preinit \
 		$(1)/etc/profile
 

package/base-files/files/etc/hotplug-preinit.json.d/10-preinit-net.json

@@ -0,0 +1,11 @@
+[
+	[ "if",
+		[ "and",
+			[ "eq", "ACTION", "add" ],
+			[ "eq", "SUBSYSTEM", "net" ]
+		],
+		[
+			[ "exec", "/sbin/preinit-netdev" ]
+		]
+	]
+]

package/base-files/files/lib/preinit/10_indicate_preinit

@@ -184,6 +184,23 @@ preinit_ip() {
 	preinit_net_echo "Doing OpenWrt Preinit\n"
 }
 
+preinit_ip_event() {
+	[ "$pi_preinit_no_failsafe" = "y" ] && return
+
+	if [ -z "$pi_ifname" ]; then
+		type set_preinit_iface > /dev/null 2>&1 && set_preinit_iface
+		pi_ifname=$ifname
+	fi
+
+	[ -n "$pi_ifname" ] || return
+
+	ip -4 -o address show dev "$pi_ifname" 2> /dev/null | \
+		grep -q "inet $pi_ip/" && return
+
+	preinit_ip_config "$pi_ifname"
+	preinit_net_echo "Doing OpenWrt Preinit\n"
+}
+
 preinit_ip_deconfig() {
 	[ -n "$pi_ifname" ] && grep -q "$pi_ifname" /proc/net/dev && {
 		local netdev vid

package/base-files/files/sbin/preinit-netdev

@@ -0,0 +1,15 @@
+#!/bin/sh
+# Copyright (C) 2026 OpenWrt.org
+
+export PATH="%PATH%"
+
+. /lib/functions.sh
+. /lib/functions/preinit.sh
+. /lib/functions/system.sh
+
+for pi_source_file in /lib/preinit/*; do
+	. $pi_source_file
+done
+
+boot_run_hook preinit_netdev
+preinit_ip_event