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    SubjectRe: sysfs permissions on dynamic attributes (led delay_on and delay_off)
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    On Sat, Jul 21, 2012 at 12:33 AM, Richard Purdie
    <richard.purdie@linuxfoundation.org> 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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