From d1581ce103db0a5db0b1761907fff9ddd6b55a8a Mon Sep 17 00:00:00 2001
From: Chen Qi <Qi.Chen@windriver.com>
Date: Wed, 9 Nov 2022 16:33:18 +0800
Subject: [PATCH] 20-resolv.conf: improve the sitation of working with systemd

systemd's resolvconf implementation ignores the protocol part.
See https://github.com/systemd/systemd/issues/25032.

When using 'dhcp server + dns server + dhcpcd + systemd', we
get an integration issue, that is dhcpcd runs 'resolvconf -d eth0.ra',
yet systemd's resolvconf treats it as eth0. This will delete the
DNS information set by 'resolvconf -a eth0.dhcp'.

Fortunately, 20-resolv.conf has the ability to build the resolv.conf
file contents itself. We can just pass the generated contents to
systemd's resolvconf. This way, the DNS information is not incorrectly
deleted. Also, it does not cause behavior regression for dhcpcd
in other cases.

Upstream-Status: Inappropriate [OE Specific]
This patch has been rejected by dhcpcd upstream.
See details in https://github.com/NetworkConfiguration/dhcpcd/pull/152

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
---
 hooks/20-resolv.conf | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/hooks/20-resolv.conf b/hooks/20-resolv.conf
index bd0b0df5..9c7721de 100644
--- a/hooks/20-resolv.conf
+++ b/hooks/20-resolv.conf
@@ -11,8 +11,12 @@ nocarrier_roaming_dir="$state_dir/roaming"
 NL="
 "
 : ${resolvconf:=resolvconf}
+resolvconf_from_systemd=false
 if command -v "$resolvconf" >/dev/null 2>&1; then
 	have_resolvconf=true
+	if [ $(basename $(readlink -f $(which $resolvconf))) = resolvectl ]; then
+		resolvconf_from_systemd=true
+	fi
 else
 	have_resolvconf=false
 fi
@@ -69,8 +73,13 @@ build_resolv_conf()
 	else
 		echo "# /etc/resolv.conf.tail can replace this line" >> "$cf"
 	fi
-	if change_file /etc/resolv.conf "$cf"; then
-		chmod 644 /etc/resolv.conf
+	if $resolvconf_from_systemd; then
+		[ -n "$ifmetric" ] && export IF_METRIC="$ifmetric"
+		"$resolvconf" -a "$ifname" <"$cf"
+	else
+		if change_file /etc/resolv.conf "$cf"; then
+			chmod 644 /etc/resolv.conf
+		fi
 	fi
 	rm -f "$cf"
 }
@@ -179,7 +188,7 @@ add_resolv_conf()
 	for x in ${new_domain_name_servers}; do
 		conf="${conf}nameserver $x$NL"
 	done
-	if $have_resolvconf; then
+	if $have_resolvconf && ! $resolvconf_from_systemd; then
 		[ -n "$ifmetric" ] && export IF_METRIC="$ifmetric"
 		printf %s "$conf" | "$resolvconf" -a "$ifname"
 		return $?
@@ -195,7 +204,7 @@ add_resolv_conf()
 
 remove_resolv_conf()
 {
-	if $have_resolvconf; then
+	if $have_resolvconf && ($if_down || ! $resolvconf_from_systemd); then
 		"$resolvconf" -d "$ifname" -f
 	else
 		if [ -e "$resolv_conf_dir/$ifname" ]; then