linux-kernel - Re: [PATCH -v2 2/2] x86: Make Linux guest support optional

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Date:	Fri, 25 Jan 2013 10:42:32 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org>, X86 ML <x86@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
	jasowang@...hat.com, Thomas Gleixner <tglx@...utronix.de>,
	JBeulich@...e.com, Borislav Petkov <bp@...e.de>,
	Dmitry Torokhov <dtor@...are.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: Re: [PATCH -v2 2/2] x86: Make Linux guest support optional

On Fri, Jan 25, 2013 at 07:32:13PM +0100, Borislav Petkov wrote:
> On Fri, Jan 25, 2013 at 10:12:51AM -0800, Dmitry Torokhov wrote:
> > Hi Borislav,
> > 
> > On Fri, Jan 25, 2013 at 06:59:37PM +0100, Borislav Petkov wrote:
> > > From: Borislav Petkov <bp@...e.de>
> > > 
> > > Put all config options needed to run Linux as a guest behind a
> > > CONFIG_HYPERVISOR_GUEST menu so that they don't get built-in by
> > > default but selected by the user. Also, move x86_hyper into an
> > > unconditionally-built compilation unit because it is exported with the
> > > non-GPL flavour and we can't know whatever uses it on the outside.
> > 
> > I am confused by this statement... How can EXPORT_SYMBOL() vs
> > EXPORT_SYMBOL_GPL() help you determining if it is used out of tree or
> > not?
> 
> Maybe this wasn't formulated clear enough - I wanted to say that with
> the !GPL flavor, any code (proprietary included) can link to those
> symbols and we cannot know who uses it and if we hide that symbol,
> someone would probably come crying.
> 
> Because if we could, I would've done trivial accessor functions which
> would return NULL when CONFIG_HYPERVISOR_GUEST is not set so that those
> cases build and boot fine, and we wouldn't have the need to have this
> symbol always present (like is the case now and I had to move it to
> setup.c).
> 
> If it were _GPL, we would've fixed all its users to switch to the
> accessors.
> 
> Makes more sense?

No, not really as EXPORT_SYMBOL_GPL() in no way implies that the code
using it lives in the mainline. Also, EXPORT_SYMBOL() does not imply
that it forms an ABI and can't be changed ever.

Thanks.

-- 
Dmitry
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