Hello Richard,

On Mon, 2025-04-07 at 19:49 +0200, Jeroen Hofstee via lists.openembedded.org wrote:

From: Jeroen Hofstee <jhofstee@victronenergy.com>

Commit 160f713917 (udev-extraconf: fix network.sh script did not
configure hotplugged interfaces, 2024-10-18) fixed ifupdown for
hotplug devices, but also calls it for non hotplug devices. That
can cause issue, since they might not expect the ifupdown from
udev, since it wasn't called before mentioned patch got merged.

For util-linux this can simply be fixed by adding --allow=hotplug.
Unfortunately busybox doesn't have that option, so a function is
added to check if the device is marked as allow-hotplug.

Since wilcards are supported adding 'allow-hotplug *' allows to
restore behaviour of mentioned patch, while this restores the
original behaviour.

Signed-off-by: Jeroen Hofstee <jhofstee@victronenergy.com>
---
 .../udev/udev-extraconf/network.sh            | 28 +++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/meta/recipes-core/udev/udev-extraconf/network.sh b/meta/recipes-core/udev/udev-extraconf/network.sh
index 500e60ae61..da79f00d5a 100644
--- a/meta/recipes-core/udev/udev-extraconf/network.sh
+++ b/meta/recipes-core/udev/udev-extraconf/network.sh
@@ -6,6 +6,34 @@ echo "$INTERFACE" | grep -q wifi && exit 0
 # udevd does clearenv(). Export shell PATH to children.
 export PATH
 
+# udev should only trigger ifupdown for interfaces marked as allow-hotplug
+# and with util-linux that is as simple as adding --allow=hotplug.
+# Busybox unfortunately doesn't have this option.
+# allow-hotplug is a pattern like eth0 /eth* /eth*/1 /eth*=eth.
+# This function checks if INTERFACE matches an allow-hotplug pattern.
+
+allow_hotplug() {
+    allow_hotplug="$(sed -n -e 's/^allow-hotplug \+\([^= ]*\).*/\1/p' /etc/network/interfaces)"
+    for pattern in $allow_hotplug; do
+        options="$(echo $pattern | sed -n -e 's,^/\?[^ /]\+/\(.*\),\1,p')"
+        value="$(echo $pattern | sed -n -e 's,^/\?\([^ /]\+\).*,\1,p')"
+        interfaces="$(ls -d /sys/class/net/$value 2>/dev/null | xargs -r -n 1 basename)"
+        if [ "$options" != "" ]; then
+            interfaces="$(echo $interfaces | awk -v n=$options '{print $n }')"
+        fi
+        echo "$interfaces" | grep -w -q "$INTERFACE"
+        if [ $? -eq 0 ]; then
+            return 0
+        fi
+    done
+
+    return 1
+}
+
+if ! allow_hotplug; then
+    exit 0
+fi
+
 # if this interface has an entry in /etc/network/interfaces, let ifupdown
 # handle it
 if grep -q "iface \+$INTERFACE" /etc/network/interfaces; then

Firstly thanks for the patch, we should try and fix issues like this. I
feel I should mention our code comes from a backdrop of resource
constrained devices and the above code makes me cringe a bit due to the
execution overhead of it.

We've purposefully kept the code called from udev and in our
initscripts relatively minimal/simple as the overhead of executing
multiple programs does build up over time. Taking the above, we have
loops, then pipelines, each of which runs more commands. Each command
has a fork/exec overhead.

Is there some way we can simplify this rather than all the shell
pipelines and loops?

The simplest solution is to patch busybox to respect  --allow=hotplug I guess. With kind regards, Jeroen