> -----Original Message-----
> From: Jacek Anaszewski [mailto:[email protected]]
>
> Hi Craig,
>
> On 08/04/2015 05:56 AM, Craig McQueen wrote:
> > I've written a udev rule to catch uevent "change" events, with the goal of
> setting LED user/group/permissions whenever trigger settings are changed.
> >
> > http://unix.stackexchange.com/a/202870/34376
> >
> > However, I've noticed that a TRIGGER uevent "change" event is generated
> every time an LED is turned off.
> >
> > E.g. in one terminal:
> > udevadm monitor -p
> >
> > In another terminal:
> > echo 0 > /sys/class/leds/beaglebone:green:usr3/brightness
> >
> > The first terminal shows:
> >
> > KERNEL[15446.374466] change
> /devices/leds/leds/beaglebone:green:usr3 (leds)
> > ACTION=change
> > DEVPATH=/devices/leds/leds/beaglebone:green:usr3
> > SEQNUM=39147
> > SUBSYSTEM=leds
> > TRIGGER=none
> >
> > This behaviour is not ideal, because I really only want this uevent if the
> trigger really has changed.
> >
> > I presume this is due to these two lines in brightness_store() in
> > led-class.c:
> > if (state == LED_OFF)
> > led_trigger_remove(led_cdev);
> >
> > What would be the recommended way to improve this, so a TRIGGER
> uevent "change" event is only generated if the trigger is actually reset to
> 'none' in this scenario?
> >
> > I've noticed this on kernel 3.14.48 running on BeagleBone Black.
> >
>
> You can define your rule so that it would not be matched when
> TRIGGER=none.
I tried adding TRIGGER!="none" as in this rule:
SUBSYSTEM=="leds", ACTION=="change", TRIGGER!="none", RUN+="/bin/chgrp -R leds
/sys%p", RUN+="/bin/chmod -R g=u /sys%p"
But the rule never seems to run. I can't figure out why not. Unless the older
version of udev I'm using (182) doesn't support !=.
Meanwhile, I have made the following local change to the kernel, which does
avoid generating a uevent every time brightness is set to 0:
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index 9d9c79f..e5700c4 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -143,7 +143,8 @@ EXPORT_SYMBOL_GPL(led_trigger_set);
void led_trigger_remove(struct led_classdev *led_cdev)
{
down_write(&led_cdev->trigger_lock);
- led_trigger_set(led_cdev, NULL);
+ if (led_cdev->trigger)
+ led_trigger_set(led_cdev, NULL);
up_write(&led_cdev->trigger_lock);
}
EXPORT_SYMBOL_GPL(led_trigger_remove);
It has the minor side-effect of not generating a uevent more than once if 'echo
none > trigger' is done repeatedly. I don't think this is a problem. (But
repeated 'echo timer > trigger' would still generate a uevent every time. I
think this is in the realm of no-one-cares.)
--
Craig McQueen
--
To unsubscribe from this list: send the line "unsubscribe linux-leds" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
