Re: sysfs permissions on dynamic attributes (led delay_on and delay_off)

From: Colin Cross
Date: Sat Jul 21 2012 - 04:26:37 EST

On Sat, Jul 21, 2012 at 12:33 AM, Richard Purdie
<richard.purdie@xxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, 2012-07-20 at 21:08 -0700, Greg KH wrote:
>> On Fri, Jul 20, 2012 at 05:46:14PM -0700, Colin Cross wrote:
>> > I'm trying to use the standard ledtrig-timer.c code to handle led
>> > blinking for notifications on an Android device, and I'm hitting some
>> > issues with setting permissions on the dynamically created delay_on
>> > and delay_off attributes. For most sysfs files, we have userspace
>> > uevent parser that watches for device add notifications and
>> > chowns/chmods attributes. This doesn't work for delay_on and
>> > delay_off, because they are created later, when "timer" is written to
>> > the trigger attribute. There is no uevent when the new files are
>> > created, and sysfs doesn't support inotify, so I don't see any way to
>> > receive an event to set the permissions. This issue exists any time
>> > that device_create_file is called after device_add.
>> >
>> > What is the appropriate way to get an event to set the permissions?
>> > Add inotify support for sysfs file creation? Send a KOBJ_CHANGE
>> > uevent in device_create_file?
>> No.
>> > Send a KOBJ_CHANGE uevent from the driver after calling
>> > device_create_file?
>> Yes.
>> > Dynamically create a timer device under /sys/class/leds/<led> so a new
>> > add uevent gets sent?
>> Ick.
>> > Promote blinking to be a core led feature instead of a trigger, so the
>> > files are always present?
>> That's the best thing, why not just do that?
> This implies we should make every trigger a core led feature and
> effectively do away with triggers. I'm not sure that makes sense.

Blinking is already effectively a core feature. It is implemented in
led-core.c so it can be used by other triggers besides timer, it's
state is stored in the led_classdev structure, not in the trigger
data, and the only thing left in ledtrig-timer.c is the sysfs files.
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