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

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Message-ID: <20120721040816.GA7313@kroah.com>
Date:	Fri, 20 Jul 2012 21:08:16 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Colin Cross <ccross@...roid.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Bryan Wu <bryan.wu@...onical.com>,
	Richard Purdie <rpurdie@...ys.net>
Subject: Re: sysfs permissions on dynamic attributes (led delay_on and
 delay_off)

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
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