linux-kernel - Re: [PATCH/RFC] core: add a function to safely try to get device driver owner

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Date:	Mon, 29 Nov 2010 21:54:10 +0100 (CET)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Jonathan Corbet <corbet@....net>
cc:	linux-kernel@...r.kernel.org, Greg KH <greg@...ah.com>
Subject: Re: [PATCH/RFC] core: add a function to safely try to get device
 driver owner

Hi Jon

On Mon, 29 Nov 2010, Jonathan Corbet wrote:

> On Mon, 29 Nov 2010 20:43:28 +0100 (CET)
> Guennadi Liakhovetski <g.liakhovetski@....de> wrote:
> 
> > When two drivers interoperate without an explicit dependency, it is often
> > required to prevent one of them from being unloaded safely by dereferencing
> > dev->driver->owner. This patch provides a generic function to do this in a
> > race-free way.
> 
> I must ask: why not, instead, make the dependency explicit?  In
> particular, this looks like an application for the proposed media
> controller code, which is meant to model the connections between otherwise
> independent devices.  The fact that your example comes from V4L2 (which is
> the current domain of the media controller) also argues that way.

Sorry, don't see a good way to do this. This function is for a general 
dependency, where you don't have that driver, we are checking for register 
with us, so, the only way to get to it is via dev->driver->owner. And I 
also don't want to move registering the device into the dependant driver 
and then wait (with a timeout) for a driver to probe with it... I just 
want to verify, whether a driver has attached to that device and whether I 
can lock it down.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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