Message-Id: <201007011600.00462.dtor@vmware.com>
Date:	Thu, 1 Jul 2010 15:59:59 -0700
From:	Dmitry Torokhov <dtor@...are.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Bruno Prémont <bonbons@...ux-vserver.org>,
	Alexander Clouter <alex@...riz.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] VMware balloon: force compiling as a module

On Thursday, July 01, 2010 03:43:47 pm Andrew Morton wrote:
> On Thu, 1 Jul 2010 15:31:50 -0700
> 
> Dmitry Torokhov <dtor@...are.com> wrote:
> > On Thursday, July 01, 2010 03:18:35 pm Andrew Morton wrote:
> > > On Tue, 29 Jun 2010 09:40:38 -0700
> > > 
> > > Dmitry Torokhov <dtor@...are.com> wrote:
> > > > On Tuesday, June 29, 2010 09:28:59 am Bruno Pr__mont wrote:
> > > > > On Tue, 29 June 2010 Alexander Clouter <alex@...riz.org.uk> wrote:
> > > > > > Dmitry Torokhov <dtor@...are.com> wrote:
> > > > > > > VMware Tools installer requires the upstream driver to be
> > > > > > > compiled as a module in order to detect its presence and avoid
> > > > > > > installing our own version on top of it. To avoid surprises
> > > > > > > with 2 versions of the driver being installed and fighting
> > > > > > > with each other, let's force the driver to be compiled as a
> > > > > > > module unless user selects CONFIG_EMBEDDED.
> > > > > > 
> > > > > > *barf*
> > > > > > 
> > > > > > This surely is a problem in the installer and not the kernel? 
> > > > > > Can you not nosey around in /sys/class/misc or where-ever your
> > > > > > driver appears? If it does not, then I would probably suggest a
> > > > > > patch to your balloon driver that dumps some details in there,
> > > > > > including module version information.
> > > > > > 
> > > > > > Eugh.
> > > > > 
> > > > > In addition, the installer may check under /sys/module/ for it (as
> > > > > for any/most code that can be built as a module), even for
> > > > > built-in code. (if balloon driver does not show up there when
> > > > > built-in it would be better to get it to show up there)
> > > > 
> > > > When driver is built-in the only thing exported in /sys/module/XXX
> > > > are module parameters.
> > > > 
> > > > We also need to handle scenario when module is not loaded into the
> > > > kernel.
> > > 
> > > - check for the /sys/module directory.
> > 
> > Empty.
> 
> But the presence of the empty /sys/module/vmware_balloon tells you that
> the driver is loaded?
> 
> Confused.

No, unfortunately a kernel module that does not use module parameters
is invisible when it is built in. If you check your box you will most
likely not see /sys/module/evdev, /sys/module/input, and so forth.

> 
> > > - if that failed, modprobe the driver
> > 
> > Succeeds since the driver name changed (we renamed it to vmware_balloon
> > before submitting into mainline to avoid confusion based on our
> > experience with pvscsi; the existing one in the wild is called
> > vmmemctl).
> > 
> > Now we have 2 drivers fighting. There is no backing device and so driver
> > core will not save us by refusing to bind to already claimed device.
> 
> If vmware_balloon is present in /sys/modules or is loaded, don't load
> vmmemctl.  And vice versa.
> 
> I dunno - it's silly for me to sit here proposing solutions.  it's
> better that you do it!

Unfortunately I do not have a good solution at the moment. I guess we'll
have to work with distributions to make sure they keep it as a module
(it also makes most sense for them since not everyone runs on our
platform).

Thanks.

-- 
Dmitry

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