linux-kernel - Re: [PATCH v2 00/16] Common Dell SMBIOS API

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Date:	Mon, 8 Feb 2016 11:29:20 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Darren Hart <dvhart@...radead.org>
Cc:	Pali Rohár <pali.rohar@...il.com>,
	Michał Kępień <kernel@...pniu.pl>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Richard Purdie <rpurdie@...ys.net>,
	Jacek Anaszewski <j.anaszewski@...sung.com>,
	platform-driver-x86@...r.kernel.org, linux-leds@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/16] Common Dell SMBIOS API

On Mon, Feb 08, 2016 at 11:20:14AM -0800, Darren Hart wrote:
> On Fri, Jan 22, 2016 at 03:48:51PM +0100, Pali Rohár wrote:
> > On Friday 22 January 2016 15:27:12 Michał Kępień wrote:
> > > Note:
> > > 
> > >     In this series (both v1 and v2) I tried to stick to the overall
> > >     concept used in dell-laptop, but in the v1 thread me and Pali also
> > >     briefly discussed his alternative ideas [1][2] as to what this API
> > >     could look like, so feel free to suggest a different approach.
> > > 
> > > [1] http://www.spinics.net/lists/platform-driver-x86/msg08260.html
> > > [2] http://www.spinics.net/lists/platform-driver-x86/msg08268.html
> > 
> > I would like to hear opinion about dell-smbios API also from other
> > people. Darren, can you look and comment it?
> 
> This is an excellently prepared series, nice work Michał.
> 
> Most of my concerns were addressed by later patches in the series. I have pushed
> a version of this 1/7 fixed per lkp (linux/io.h) and 7/16 with a corrected body
> as I sent in reply to that patch. This is on my tree as the dell-smbios branch.
> 
> My only major concern is module load order dependencies. Inter-module
> dependencies are frowned upon with good reason, the kernel load ordering is
> non-deterministic and it's possible, for example, for dell-laptop to fail to
> find the symbols exported by dell-smbios under certain conditions.
> 
> I have worked around this in the past with things like the following:
> 
> #ifdef MODULE
> #ifdef CONFIG_FOO_MODULE
> 	if (request_module("foo"))
> 		return -ENODEV;
> #endif
> #endif
> 
> Something like the above may be necessary for dell-smbios in dell-laptop,
> dell-wmi, and dell-leds now that they depend on the dell-smbios exported
> functions.
> 
> Cc Greg in case there is a better way to handle this that I'm not aware of.

No need to request_module anything, the symbol resolution should pull
the dependant module in automagically when you do a 'modprobe',
otherwise the symbols would never be found.

thanks,

greg k-h