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From: Paolo Bonzini <pbonzini@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: kvm@vger.kernel.org, "Radim Krčmář" <rkrcmar@redhat.com>,
	"Haiyang Zhang" <haiyangz@microsoft.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	devel@linuxdriverproject.org, "Ingo Molnar" <mingo@redhat.com>,
	"Roman Kagan" <rkagan@virtuozzo.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Denis V . Lunev" <den@openvz.org>,
	"Thomas Gleixner" <tglx@linutronix.de>
Subject: Re: [PATCH 12/15] hyperv: move VMBus connection ids to uapi
Date: Wed, 21 Dec 2016 18:25:58 +0100	[thread overview]
Message-ID: <4737c664-e6f6-fede-9f80-4c757de8bc9b@redhat.com> (raw)
In-Reply-To: <20161221154348.GA31401@infradead.org>



On 21/12/2016 16:43, Christoph Hellwig wrote:
> On Wed, Dec 21, 2016 at 04:39:18PM +0100, Paolo Bonzini wrote:
>> That said, there are precedents in using UAPI this way for PV
>> interfaces.  See for example include/uapi/linux/virtio*.h and
>> arch/x86/include/uapi/asm/kvm_para.h.
> 
> We have all kinds of historical examples, but most of them turned
> into a major pain sooner or later - my favourite example are the
> SCSI protocol headers.

Mine too, and because of how uapi/ was created there are quite a few
such historical headers (my favourite is cuda.h, just because of the name).

> Protocols needs to stay compatible on the (virtual) wire, but not
> on the language level.  Locking us into the strict UABI policies
> for them just make someone life horrible further down the road.

The ABI for this kind of thing is not changing much anyway, because it's
the hardware or processor or (as in this case) hypervisor ABI.

The more interesting question is about the API, and here in the end it
seems to be up to the maintainer.

Some have explicitly asked to move stuff *out* of UAPI, for example the
x86 guys have removed msr-index.h from UAPI recently.  Others are okay
with it and they simply aren't strict on cleanups that might break the
*programming* interface, as in patch 15 of this series.  See for example
pci_regs.h commit 846fc70986a6, "PCI/AER: Rename PCI_ERR_UNC_TRAIN to
PCI_ERR_UNC_UND", everybody just moved on and QEMU adjusted its use of
PCI_ERR_UNC_TRAIN.

Having this in UAPI has been convenient for QEMU, but of course the
kernel couldn't care less.  So if KY prefers to have the header outside
UAPI, we will just follow suit...

Paolo

  reply	other threads:[~2016-12-21 17:26 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-20 15:55 [PATCH 00/15] hyperv: more stuff to uapi + cleanup Roman Kagan
2016-12-20 15:55 ` [PATCH 01/15] hyperv: consolidate TSC ref page definitions Roman Kagan
2016-12-20 20:57   ` KY Srinivasan
2016-12-21  6:25     ` Roman Kagan
2016-12-20 15:55 ` [PATCH 02/15] hyperv: uapi-fy synic event flags definitions Roman Kagan
2016-12-20 17:24   ` Stephen Hemminger
2016-12-21  6:33     ` Roman Kagan
2016-12-21 10:58   ` kbuild test robot
2016-12-21 18:58   ` KY Srinivasan
2016-12-20 15:55 ` [PATCH 03/15] hyperv: use standard bitops Roman Kagan
2016-12-21 12:00   ` Olaf Hering
2016-12-21 13:23     ` Roman Kagan
2016-12-22 12:33       ` Paolo Bonzini
2016-12-21 19:08   ` KY Srinivasan
2016-12-20 15:55 ` [PATCH 04/15] hyperv: define VMBus message type Roman Kagan
2016-12-20 15:55 ` [PATCH 05/15] hyperv: GFP_ATOMIC -> GFP_KERNEL Roman Kagan
2016-12-20 15:55 ` [PATCH 06/15] hyperv: avoid unnecessary vmalloc Roman Kagan
2016-12-21 19:19   ` KY Srinivasan
2016-12-20 15:55 ` [PATCH 07/15] hyperv: dedup cpuid definitions Roman Kagan
2016-12-20 15:55 ` [PATCH 08/15] hyperv: dedup crash msr related definitions Roman Kagan
2016-12-20 15:55 ` [PATCH 09/15] hyperv: unify Hyper-V msr definitions Roman Kagan
2016-12-20 15:55 ` [PATCH 10/15] hyperv: uapi-fy PostMessage and SignalEvent hypercall structures Roman Kagan
2016-12-21 19:27   ` KY Srinivasan
2016-12-20 15:55 ` [PATCH 11/15] hyperv: uapi-fy monitored notification structures Roman Kagan
2016-12-20 15:55 ` [PATCH 12/15] hyperv: move VMBus connection ids to uapi Roman Kagan
2016-12-20 17:25   ` Stephen Hemminger
2016-12-21  6:29     ` Roman Kagan
2016-12-21 12:18       ` Christoph Hellwig
2016-12-21 12:59         ` Roman Kagan
2016-12-21 14:26           ` Christoph Hellwig
2016-12-21 14:39             ` Roman Kagan
2016-12-21 15:39             ` Paolo Bonzini
2016-12-21 15:43               ` Christoph Hellwig
2016-12-21 17:25                 ` Paolo Bonzini [this message]
2016-12-21 17:50                 ` Stephen Hemminger
2016-12-21 17:53                   ` Paolo Bonzini
2016-12-21 17:58                   ` Christoph Hellwig
2016-12-21 18:02                     ` Stephen Hemminger
2016-12-21 19:54                       ` KY Srinivasan
2016-12-28 17:09                         ` Roman Kagan
2016-12-29 18:29                           ` Stephen Hemminger
2017-01-02  8:19                           ` Paolo Bonzini
2017-01-09  8:32                             ` Roman Kagan
2017-01-09  8:40                               ` hpa
2017-01-09  8:58                                 ` Roman Kagan
2017-01-09  9:02                                 ` Paolo Bonzini
2017-01-02 19:39                           ` Stephen Hemminger
2017-01-03  9:32                             ` Paolo Bonzini
2016-12-20 15:56 ` [PATCH 13/15] hyperv: move function close to its only callsite Roman Kagan
2016-12-20 15:56 ` [PATCH 14/15] hyperv_vmbus: drop unused definitions Roman Kagan
2016-12-20 15:56 ` [PATCH 15/15] hyperv: redefine hv_message without bitfields Roman Kagan
2016-12-21 18:00 ` [PATCH 00/15] hyperv: more stuff to uapi + cleanup KY Srinivasan
2016-12-28 16:57   ` Roman Kagan
2016-12-30 19:45     ` KY Srinivasan

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