linux-kernel - Re: modalias char-major-10-130

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Message-ID: <20130705171824.GB29175@roeck-us.net>
Date:	Fri, 5 Jul 2013 10:18:24 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Jean Delvare <jdelvare@...e.de>
Cc:	Wim Van Sebroeck <wim@...ana.be>, linux-watchdog@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: modalias char-major-10-130

On Wed, Jul 03, 2013 at 02:33:23PM +0200, Jean Delvare wrote:
> Hi Wim,
> 
> All watchdog drivers include:
> 
> MODULE_ALIAS_MISCDEV(WATCHDOG_MINOR);
> 
> which causes a modalias char-major-10-130 to be added to every watchdog
> driver module. As a result, any access to /dev/watchdog on a system with
> no watchdog driver loaded and working will result in an attempt to load
> several dozen drivers. At best one or two will actually work, the others
> will:
> 
> * Waste time failing to load.
> * Waste memory succeeding to load but not finding any device to bind to.
> * Pollute the kernel log.
> * Sometimes even load while they should not and break the system. I just
> had a report about advantechwdt doing that on some systems.
> 
> And the attempt order will presumably be random, so it might as well
> load softdog before a hardware-based watchdog which would have been
> preferred.
> 
> This looks so 90s. Drivers for enumerated devices have hardware-based
> modaliases, so char-major-10-130 shouldn't be needed. Other drivers
> should certainly not be loaded randomly if they need to poke the
> hardware to detect the presence of a supported device.
> 
> My opinion is that the char-major-10-130 modalias should ONLY be defined
> by user-space, when the user knows he/she needs a watchdog driver which
> doesn't support auto-loading via hardware-based auto-loading.
> 
> So, can we please get rid of all these
> MODULE_ALIAS_MISCDEV(WATCHDOG_MINOR) statements? They do more harm than
> good as far as I can see.
> 
Agreed.

Can you submit a set of patches ? I'll be happy to add my Reviewed-by: tag
to it. Of course that won't guarantee acceptance ;).

Thanks,
Guenter
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