> -----Original Message----- > From: Jacek Anaszewski [mailto:jacek.anaszewski@xxxxxxxxx] > > 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 majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
