99-systemd.rules.in: guard systemd-backlight udev rules by ENABLE_BACKLIGHT

Linux kernel will, as documented in drivers/video/backlight/backlight.c,
report changes to a backlights brightness as a uevent (ACTION=change).

systemd-udev will consume the uevent, match on this rule and try to
activate the systemd-backlight service for the backlight. BUT when
systemd is not compiled with backlight support, this will lead to
failure that is reported in the journal.

Since the failure to activate systemd-backlight and subsequent failure
log entry happens on every backlight brightness change, we found the
resulting logspam during regular operation excessive and came up with
this patch to mitigate it.

The conditional is also extended to "*kbd_backlight" match, since
even though we did not investigate to see if the logspam would be
similar, the unconditional match to activate systemd-backlight here
would also not make sense when the feature is not compiled in.

Signed-off-by: Simon Braunschmidt <simon.braunschmidt@iba-group.com>

diff --git a/rules.d/99-systemd.rules.in b/rules.d/99-systemd.rules.in
index 3dbba1f850dbee233c8f0ae14bbda5642f6adb21..c0defc31de729e90c6d24ec64445507eae68d504 100644 (file)
--- a/rules.d/99-systemd.rules.in
+++ b/rules.d/99-systemd.rules.in
@@ -65,10 +65,12 @@ SUBSYSTEM=="udc", ACTION=="add", TAG+="systemd", ENV{SYSTEMD_WANTS}+="usb-gadget
 # Apply sysctl variables to network devices (and only to those) as they appear.
 ACTION=="add", SUBSYSTEM=="net", KERNEL!="lo", RUN+="{{ROOTLIBEXECDIR}}/systemd-sysctl --prefix=/net/ipv4/conf/$name --prefix=/net/ipv4/neigh/$name --prefix=/net/ipv6/conf/$name --prefix=/net/ipv6/neigh/$name"
 
+{% if ENABLE_BACKLIGHT %}
 # Pull in backlight save/restore for all backlight devices and
 # keyboard backlights
 SUBSYSTEM=="backlight", TAG+="systemd", IMPORT{builtin}="path_id", ENV{SYSTEMD_WANTS}+="systemd-backlight@backlight:$name.service"
 SUBSYSTEM=="leds", KERNEL=="*kbd_backlight", TAG+="systemd", IMPORT{builtin}="path_id", ENV{SYSTEMD_WANTS}+="systemd-backlight@leds:$name.service"
+{% endif %}
 
 # Pull in rfkill save/restore for all rfkill devices
 SUBSYSTEM=="rfkill", ENV{SYSTEMD_RFKILL}="1"