linux-kernel - Re: [PATCH] VMware balloon: force compiling as a module

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Message-Id: <201007011531.52291.dtor@vmware.com>
Date:	Thu, 1 Jul 2010 15:31:50 -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 03:18:35 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.

> 
> - 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 that failed, error out
> 
> The patch really is pretty icky.  Adding restrictions to kernel
> configuration to work around problems in some installer program?

It is probably not the prettiest patch, I agree, but users still have
an option of building this stuff in if they care that much
(CONFIG_EMBEDDED).

Thanks.

-- 
Dmitry

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