linux-kernel - Re: [PATCH 2/3] gpiolib: add support for having symlinks under gpio class directory

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Date:	Fri, 11 Dec 2009 07:38:14 -0800
From:	Greg KH <gregkh@...e.de>
To:	Jani Nikula <ext-jani.1.nikula@...ia.com>
Cc:	bn@...sdigital.com,
	"dbrownell@...rs.sourceforge.net" <dbrownell@...rs.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dsilvers@...tec.co.uk" <dsilvers@...tec.co.uk>,
	"ben@...tec.co.uk" <ben@...tec.co.uk>,
	"Bityutskiy Artem (Nokia-D/Helsinki)" <Artem.Bityutskiy@...ia.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/3] gpiolib: add support for having symlinks under
	gpio class directory

On Fri, Dec 11, 2009 at 10:41:40AM +0200, Jani Nikula wrote:
> Let's see. 'udevadm monitor --env' gives me this when I 'echo add >
> uevent' for an exported gpio #5:
> 
> UDEV  [1230784956.241303] add      /class/gpio/gpio5 (gpio)                     
> UDEV_LOG=3                                                                      
> ACTION=add                                                                      
> DEVPATH=/class/gpio/gpio5                                                       
> SUBSYSTEM=gpio                                                                  
> SEQNUM=930                                                                      
> UDEVD_EVENT=1
> 
> Now *assuming* we had /sys/class/gpio/gpioN/name, I could create very
> crude udev rules along the lines of this:
> 
> SUBSYSTEM=="gpio", ACTION=="add", ATTR{name}!="", RUN="/bin/ln -s /sys$devpath /tmp/gpio-$attr{name}"
> SUBSYSTEM=="gpio", ACTION=="remove", ATTR{name}!="", RUN="/bin/rm /tmp/gpio-$attr{name}"
> 
> Not exactly pretty, but seems to work (using another attr for testing).
> Is there a more elegant way of doing this with udev when there are no
> device nodes? Or is it even sensible to use udev without the device
> nodes? And what would be the right place for the symlinks?

Kay said he didn't like you creating symlinks in /dev with udev, but
this looks ok to me.

> *If* we got that working in a sensible fashion, it'd be a matter of
> adding the "name" attribute to each gpio.

Yup, just use whatever you were wanting to use as the symlink name, it
seems that logic was already done.

thanks.

greg k-h
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