linux-kernel - Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels

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Date:	Mon, 07 Nov 2011 15:03:00 -0500
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Vince Weaver <vince@...ter.net>,
	Pekka Enberg <penberg@...helsinki.fi>,
	"Ted Ts'o" <tytso@....edu>, Pekka Enberg <penberg@...nel.org>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Avi Kivity <avi@...hat.com>,
	"kvm@...r.kernel.org list" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
	qemu-devel Developers <qemu-devel@...gnu.org>,
	Alexander Graf <agraf@...e.de>,
	Blue Swirl <blauwirbel@...il.com>,
	=?iso-8859-1?Q?Am=E9rico?= Wang 
	<xiyou.wangcong@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels

Ingo Molnar <mingo@...e.hu> writes:

> [...]
>> It's problem enough that there's no way to know what version of the 
>> perf_event abi you are running against and we have to guess based 
>> on kernel version.  This gets "fun" because all of the vendors have 
>> backported seemingly random chunks of perf_event code to their 
>> older kernels.
>
> The ABI design allows for that kind of flexible extensibility, and 
> it's one of its major advantages.
>
> What we *cannot* protect against is you relying on obscure details of 
> the ABI [...]

Is there some documentation that clearly spells out which parts of the
perf syscall userspace ABI are "obscure" and thus presumably
changeable?

> [...]  The usual ABI rules also apply: we'll revert everything that
> breaks the ABI - but for that you need to report it *in time* [...]

If the ABI is so great in its flexible extensibility, how come it
can't be flexibly extended without having to passing the burden of
compatibility testing & reversion-yawping to someone else?


- FChE
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