lkml.org 
[lkml]   [2012]   [Jul]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: sysfs permissions on dynamic attributes (led delay_on and delay_off)
    From
    Date
    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@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.

    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...

    Cheers,

    Richard





    \
     
     \ /
      Last update: 2012-07-21 14:01    [W:2.789 / U:0.168 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site