linux-kernel - Re: sysfs permissions on dynamic attributes (led delay_on and delay

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Date:	Sat, 21 Jul 2012 08:33:30 +0100
From:	Richard Purdie <richard.purdie@...uxfoundation.org>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Colin Cross <ccross@...roid.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Bryan Wu <bryan.wu@...onical.com>
Subject: Re: sysfs permissions on dynamic attributes (led delay_on and
 delay_off)

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.

Cheers,

Richard

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