Re: sysfs permissions on dynamic attributes (led delay_on anddelay_off)
From: Richard Purdie
Date: Sat Jul 21 2012 - 07:21:54 EST
On Sat, 2012-07-21 at 01:26 -0700, Colin Cross wrote:
> 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.
Having the attributes present all the time leads to some nasty questions
like how the on/off delays interact with things like say a network
activity trigger. Not all triggers are going to respect these delay
values and I can imagine a whole new set of nasty bug reports with no
easy solutions if this change is made...
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