linux-kernel - Re: [Patch -mm 0/3] RFC: module unloading vs. release function

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Message-ID: <20070417094934.2709cd80@gondolin.boeblingen.de.ibm.com>
Date:	Tue, 17 Apr 2007 09:49:34 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Greg KH <greg@...ah.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Tejun Heo <htejun@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [Patch -mm 0/3] RFC: module unloading vs. release function

On Mon, 16 Apr 2007 17:02:46 -0400 (EDT),
Alan Stern <stern@...land.harvard.edu> wrote:

> > No, only the core module has to stay. For example, every time you
> > register an input device you pin input.ko as it is the module that
> > provides ->release() method for input devices. You can freely unload
> > psmouse, or hid or your favorite joystick but input has to stay until
> > last reference to the input device is dropped. serio and gameport work
> > the same way.
> > 
> > I think the requirement that one is not able to unload a core
> > subsystem module untill all users are dropped off is ok - you can't
> > unload it anyway until you unload all drivers that reference its
> > exported functions and once you unload all the drivers data objects
> > will drop off pretty quickly.
> 
> The problem is that sometimes devices are owned by modules that aren't
> core subsystem modules.  Or the code using a device doesn't depend on the
> device's owner module and therefore doesn't pin it.

Yes. For example, zfcp creates some devices itself that don't have any
relation to the ccw bus. (Other s390 drivers need a simple device; they
use a generic device creation routine that uses a release function that
is always built into s390 kernels.)
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