From: Andre Eikmeyer <dev@deq.rocks>
Date: Sun, 2 Aug 2026 13:48:41 +0000 (+0200)
Subject: udev: derive path ID for PNP devices from ACPI firmware node
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=6044c31038a2c24294f29df40a0cae9c19cc5e9b;p=thirdparty%2Fsystemd.git

udev: derive path ID for PNP devices from ACPI firmware node

PNP devices may represent ACPI-enumerated hardware but do not have a
parent type supported by path_id. Consequently, importing path_id fails
even when the PNP device exposes a stable ACPI firmware_node. This also
prevents later assignments in rules such as the systemd-backlight
activation rule from taking effect.

Resolve the PNP device's firmware_node and use its ACPI sysname for the
path component. This gives PNP-backed devices the same stable identity
as their firmware representation.

Add a regression test using an RTC device below a PNP parent with an
ACPI firmware node.
---

diff --git a/src/udev/udev-builtin-path_id.c b/src/udev/udev-builtin-path_id.c
index 8ae66b30f26..32028c83f6b 100644
--- a/src/udev/udev-builtin-path_id.c
+++ b/src/udev/udev-builtin-path_id.c
@@ -677,6 +677,30 @@ static void add_id_tag(UdevEvent *event, const char *path) {
         (void) udev_builtin_add_property(event, "ID_PATH_TAG", tag);
 }
 
+static int handle_pnp(sd_device *parent, char **path) {
+        _cleanup_(sd_device_unrefp) sd_device *firmware_node = NULL;
+        const char *sysname;
+        int r;
+
+        assert(parent);
+        assert(path);
+
+        r = sd_device_new_child(&firmware_node, parent, "firmware_node");
+        if (r < 0)
+                return r;
+
+        if (device_in_subsystem(firmware_node, "acpi") <= 0)
+                return -ENODEV;
+
+        r = sd_device_get_sysname(firmware_node, &sysname);
+        if (r < 0)
+                return r;
+
+        path_prepend(path, "acpi-%s", sysname);
+
+        return 0;
+}
+
 static int builtin_path_id(UdevEvent *event, int argc, char *argv[]) {
         sd_device *dev = ASSERT_PTR(ASSERT_PTR(event)->dev);
         _cleanup_(sd_device_unrefp) sd_device *dev_other_branch = NULL;
@@ -749,6 +773,10 @@ static int builtin_path_id(UdevEvent *event, int argc, char *argv[]) {
                                 path_prepend(&compat_path, "acpi-%s", sysname);
                         parent = skip_subsystem(parent, "acpi");
                         supported_parent = true;
+                } else if (device_in_subsystem(parent, "pnp") > 0) {
+                        if (handle_pnp(parent, &path) >= 0)
+                                supported_parent = true;
+                        parent = skip_subsystem(parent, "pnp");
                 } else if (device_in_subsystem(parent, "xen") > 0) {
                         path_prepend(&path, "xen-%s", sysname);
                         if (compat_path)
diff --git a/test/sys-script.py b/test/sys-script.py
index be45a211e21..550fb289dfe 100755
--- a/test/sys-script.py
+++ b/test/sys-script.py
@@ -10584,6 +10584,7 @@ f('sys/devices/pnp0/00:07/rtc/rtc0/name', 0o644, b'rtc_cmos\n')
 f('sys/devices/pnp0/00:07/rtc/rtc0/time', 0o644, b'02:30:51\n')
 f('sys/devices/pnp0/00:07/rtc/rtc0/uevent', 0o644, b'''MAJOR=253
 MINOR=0
+DEVNAME=rtc0
 ''')
 d('sys/devices/pnp0/00:07/rtc/rtc0/power', 0o755)
 f('sys/devices/pnp0/00:07/rtc/rtc0/power/wakeup', 0o644, b'\n')
diff --git a/test/test-udev.py b/test/test-udev.py
index da5d41efe01..c2ee8b1bc14 100755
--- a/test/test-udev.py
+++ b/test/test-udev.py
@@ -2071,6 +2071,17 @@ SUBSYSTEMS=="scsi", PROGRAM=="/bin/bash -c \"printf %%s 'foo1 foo2' | grep 'foo1
         KERNEL=="sda", ENV{ID_PATH}=="?*", SYMLINK+="disk/by-path/$env{ID_PATH}"
         ''',
     ),
+    Rules.new(
+        'builtin path_id for PNP device with ACPI firmware node',
+        Device(
+            '/devices/pnp0/00:07/rtc/rtc0',
+            exp_links=['rtc/by-path/acpi-PNP0B00:00'],
+        ),
+        rules=r'''
+        KERNEL=="rtc0", IMPORT{builtin}="path_id"
+        KERNEL=="rtc0", ENV{ID_PATH}=="?*", SYMLINK+="rtc/by-path/$env{ID_PATH}"
+        ''',
+    ),
     Rules.new(
         'add and match tag',
         Device(