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

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Message-ID: <20101129214128.GA9691@kroah.com>
Date:	Mon, 29 Nov 2010 13:41:28 -0800
From:	Greg KH <greg@...ah.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC] core: add a function to safely try to get device
 driver owner

On Mon, Nov 29, 2010 at 09:54:10PM +0100, Guennadi Liakhovetski wrote:
> 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.

Wait, what?  The device is already bound to a driver, right, so why
would you care about "locking" the module into memory?  What could this
possibly be used for?

> 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.

Who cares if a driver is attached to any device?  And again, why would
you want to "lock it down"?

confused,

greg k-h
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