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Date: Fri, 20 Jul 2012 21:08:16 -0700
From: Greg KH <gregkh@linuxfoundation.org>
To: Colin Cross <ccross@android.com>
Cc: lkml <linux-kernel@vger.kernel.org>, Bryan Wu <bryan.wu@canonical.com>,
        Richard Purdie <rpurdie@rpsys.net>
Subject: Re: sysfs permissions on dynamic attributes (led delay_on and
 delay_off)
Message-ID: <20120721040816.GA7313@kroah.com>
References: <CAMbhsRTX=t4UMfmrJRyXidSTWXvaC5L9aFdTFL03wYYKrUE5qw@mail.gmail.com>
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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?

thanks,

greg k-h