linux-kernel - Re: Missing removal of sysfs attributes in gpiolib

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Date:	Wed, 28 Aug 2013 11:44:33 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Grant Likely <grant.likely@...aro.org>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: Missing removal of sysfs attributes in gpiolib

On Wed, Aug 28, 2013 at 11:31:39AM -0700, Greg Kroah-Hartman wrote:
> On Wed, Aug 28, 2013 at 10:57:17AM -0700, Guenter Roeck wrote:
> > Hi,
> > 
> > I noticed that gpiolib does not explicitly remove the sysfs attributes it
> > created when exporting a gpio pin when the pin is unexported, ie when the
> > associated device is removed.
> > 
> > Are those attributes auto-removed when device_unregister() is called ?
> 
> Yes they are.
> 
Does that mean that the explicit attribute removal that is implemented
in many drivers can be dropped ? That might save a lot of code.

> > Sorry if this is a dumb question - I have not noticed this anywhere else,
> > and I don't seem to be able to find the code actually performing auto-removal
> > of manually created attributes, so I wonder if this is a bug or intentional.
> 
> Hm, I thought this was listed in the kobject.txt documentation file, but
> I don't seem to find it there.
> 
Would be great if this could be documented somewhere (unless it is and
I didn't find it ;). I would volunteer to do it myself, but I have no idea
what the conditions for auto-removal are nor how to phrase it, nor where
to put it.

> But, ideally you aren't creating individual attributes directly, you are
> using attribute groups for the device, right?
> 
gpiolib does currently create individual attributes as well as attribute
groups after registering the device. I was in the process of converting
it to use device_create_with_groups() when I noticed that there is no
removal, so I wondered.

I take it that attribute groups created with sysfs_create_group()
are auto-removed as well, correct ?  

Thanks,
Guenter
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