Re: [PATCH 12/15] hyperv: move VMBus connection ids to uapi

From: Roman Kagan <rkagan@virtuozzo.com>
To: KY Srinivasan <kys@microsoft.com>
Cc: "Stephen Hemminger" <stephen@networkplumber.org>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Vitaly Kuznetsov" <vkuznets@redhat.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"Denis V . Lunev" <den@openvz.org>,
	"Haiyang Zhang" <haiyangz@microsoft.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
	"Thomas Gleixner" <tglx@linutronix.de>
Subject: Re: [PATCH 12/15] hyperv: move VMBus connection ids to uapi
Date: Wed, 28 Dec 2016 20:09:44 +0300	[thread overview]
Message-ID: <20161228170943.GB14702@rkaganb.sw.ru> (raw)
In-Reply-To: <DM5PR03MB2490AAE96B779C49A777FD15A0930@DM5PR03MB2490.namprd03.prod.outlook.com>

On Wed, Dec 21, 2016 at 07:54:11PM +0000, KY Srinivasan wrote:
> 
> 
> > -----Original Message-----
> > From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> > Sent: Wednesday, December 21, 2016 10:03 AM
> > To: Christoph Hellwig <hch@infradead.org>
> > Cc: Paolo Bonzini <pbonzini@redhat.com>; Roman Kagan
> > <rkagan@virtuozzo.com>; Radim Krčmář <rkrcmar@redhat.com>; KY
> > Srinivasan <kys@microsoft.com>; Vitaly Kuznetsov
> > <vkuznets@redhat.com>; kvm@vger.kernel.org; Denis V . Lunev
> > <den@openvz.org>; Haiyang Zhang <haiyangz@microsoft.com>;
> > x86@kernel.org; linux-kernel@vger.kernel.org; Ingo Molnar
> > <mingo@redhat.com>; H. Peter Anvin <hpa@zytor.com>;
> > devel@linuxdriverproject.org; Thomas Gleixner <tglx@linutronix.de>
> > Subject: Re: [PATCH 12/15] hyperv: move VMBus connection ids to uapi
> > 
> > On Wed, 21 Dec 2016 09:58:36 -0800
> > Christoph Hellwig <hch@infradead.org> wrote:
> > 
> > > On Wed, Dec 21, 2016 at 09:50:49AM -0800, Stephen Hemminger wrote:
> > > > Lastly, there is licensing issues on headers. It would be good to have any
> > > > userspace ABI headers licensed with a more liberal license so that BSD
> > and DPDK drivers
> > > > could use them directly. Right now each one reinvents.
> > >
> > > Microsoft could easily solves this problem by offering a suitably
> > > liberally licensed header documenting the full HyperV guest protocol
> > > that Linux and other projects could use.
> > 
> > The issue is if same header file mixes kernel and userspace API stuff.
> > 
> > Once the files are arranged right, I will submit trivial change to comments
> > to indicate the liberal licensing of userspace API headers.
> 
> Let us take this one step at a time. I know for a fact that not all the guest host
> protocols on Hyper-V are guaranteed to be stable. Some of the protocols are part of
> the published MSFT standards such RNDIS and these obviously are guaranteed to be
> stable. For the rest it is less clear. The fact that we need to ensure compatibility of existing
> Windows guests tells me that any host side changes will be versioned and the hosts will always
> support older guests.
> 
> I would like to minimize what we include in the uapi header; especially when MSFT has made no guarantees
> with regards how  they may be evolved. I will also work on getting some clarity on both stability and
> under what license we would expose the uapi header.

Am I correct assuming that QEMU is currently the only user of
arch/x86/include/uapi/asm/hyperv.h?

Then I think we're fine withdrawing it from uapi as a whole and letting
QEMU pull it in through its header-harvesting scripts (as does now
anyway).  This would lift all licensing and longterm API stability
expectations.

Roman.