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Udev rule for /sys/class/leds/
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AustrianCoder
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Posts: 258
Location: �sterreich

PostPosted: Wed Aug 22, 2012 2:33 pm    Post subject: Udev rule for /sys/class/leds/ Reply with quote

Hi all.

I am running in some issues with changing permissions of /sys/class/leds/

Code:

root@OT:~# ls /sys/class/leds/buzzer/ -l
total 0
-rw-r--r-- 1 root root 4096 Aug 22 13:49 brightness
-rw-r--r-- 1 root root 4096 Aug 22 13:49 delay_off
-rw-r--r-- 1 root root 4096 Aug 22 13:49 delay_on
lrwxrwxrwx 1 root root    0 Aug 22 13:49 device -> ../../../leds-gpio.0
-r--r--r-- 1 root root 4096 Aug 22 13:49 max_brightness
lrwxrwxrwx 1 root root    0 Aug 22 13:45 subsystem -> ../../../../../class/leds
-rw-r--r-- 1 root root 4096 Aug 22 13:49 trigger
-rw-r--r-- 1 root root 4096 Aug 22 13:45 uevent


I want that every user could write to brightness trigger and delay_on/off if these files exist. The biggest
problem is that if I change the trigger to none and back to timer only root can access delay_on/off as
these two files got removed and recreated during trigger change.

This is my try for an udev rule:
Code:

SUBSYSTEM=="leds", MODE="0777"


And here are some other useful informations:
Code:

root@OT:~# udevadm info --path=/sys/class/leds/buzzer --query=all  --attribute-walk
custom logging function 0xb8a4b008 registered
selinux=0
calling: info
device 0xb8a4b078 has devpath '/devices/platform/leds-gpio.0/leds/buzzer'

Udevadm info starts with the device specified by the devpath and then
walks up the chain of parent devices. It prints for every device
found, all possible attributes in the udev rules key format.
A rule to match, can be composed by the attributes of the device
and the attributes from one single parent device.

  looking at device '/devices/platform/leds-gpio.0/leds/buzzer':
    KERNEL=="buzzer"
    SUBSYSTEM=="leds"
    DRIVER==""
    ATTR{brightness}=="0"
    ATTR{max_brightness}=="255"
    ATTR{trigger}=="none [timer] heartbeat "
    ATTR{delay_on}=="0"
    ATTR{delay_off}=="0"

device 0xb8a4b3f0 has devpath '/devices/platform/leds-gpio.0'
  looking at parent device '/devices/platform/leds-gpio.0':
    KERNELS=="leds-gpio.0"
    SUBSYSTEMS=="platform"
    DRIVERS=="leds-gpio"
    ATTRS{modalias}=="platform:leds-gpio"

device 0xb8a4b610 has devpath '/devices/platform'
  looking at parent device '/devices/platform':
    KERNELS=="platform"
    SUBSYSTEMS==""
    DRIVERS==""


I am quite happy about any hint
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avx
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PostPosted: Wed Aug 22, 2012 10:24 pm    Post subject: Reply with quote

Don't know much about udev, but if only the goal matters, why not just simply create a file like /etc/local.d/set_led_perms.start and use a `chmod 777 $files` in it?
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AustrianCoder
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Joined: 11 Oct 2003
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Location: �sterreich

PostPosted: Wed Sep 05, 2012 6:36 am    Post subject: Reply with quote

Sorry for the late answer.

The problem is that device nodes gets created and deleted if I change the trigger. And the new created files
are only accessible as root.
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grey_dot
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Joined: 15 Jul 2012
Posts: 142

PostPosted: Wed Sep 05, 2012 8:00 am    Post subject: Reply with quote

udev doesn't manage /sys filesystem, only the /dev one. /sys is totally managed by kernel.

upd: and, in case you might ask, placing led interface in /dev will most likely require modifing the corresponding kernel driver. Though, it might not be such a bad idea :) Btw, FreeBSD has /dev/led/ directory with nodes to manage leds status.
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avx
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PostPosted: Wed Sep 05, 2012 1:51 pm    Post subject: Reply with quote

AustrianCoder wrote:
Sorry for the late answer.

The problem is that device nodes gets created and deleted if I change the trigger. And the new created files
are only accessible as root.
Then setup a some kind of watching script, around inotify maybe, that triggers on demand.
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PostPosted: Wed Sep 05, 2012 2:17 pm    Post subject: Reply with quote

avx wrote:
AustrianCoder wrote:
Sorry for the late answer.

The problem is that device nodes gets created and deleted if I change the trigger. And the new created files
are only accessible as root.
Then setup a some kind of watching script, around inotify maybe, that triggers on demand.


Changing permissions on /sys files is not a really wise idea. I'd write a suid script that echoes whatever needed to those files instead.
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