linux-kernel - Re: ABI coupling to hypervisors via CONFIG

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Date:	Fri, 9 Mar 2007 21:50:23 +0100 (MET)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Zachary Amsden <zach@...are.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	john stultz <johnstul@...ibm.com>, akpm@...ux-foundation.org,
	LKML <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@...e.de>,
	Chris Wright <chrisw@...s-sol.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: ABI coupling to hypervisors via CONFIG_PARAVIRT

Hello,


On Mar 9 2007 20:24, Ingo Molnar wrote:
>* Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
>>On Fri, 9 Mar 2007, Ingo Molnar wrote:
>>> 
>>> yes - but we already support the raw hardware ABI, in the native 
>>> kernel.
>> 
>> Why do you continue to call paravirt an ABI?
>> We got over that. It's not. It's an API.
>> VMI is an ABI.
>
>Unfortunately i still dont see where i'm wrong, and i'm really trying to 
>understand your argument. Is your argument that as long as an ABI (VMI) 
>is never directly used but only used via wrapper functions 
>(paravirt_ops), it has no effects whatsoever on the flexibility of the 
>rest of the software and ceases to have any negative ABI effects? [...]

As far as I understand and recognize it,


  [have monospaced font]

  paravirt struct      struct file_operations / {ALSA | OSS}
   ^                    ^
   |      <- API ->     |
   v                    v
  VMI                  /dev/dsp
   ^                    ^
   |      <- ABI ->     |
   v                    v
  product              userspace app


I think the sound example to the right really shows it. /dev/dsp has a
consistent ABI on a ton of systems. The API below it, varies. Linux got
file_operations and ALSA. Solaris/BSD may have its
vnode-and-so-on-functions and some sort of OSS.

Hope this helps (and more, I hope it's accurate - please correct me if I
am wrong.)



Jan
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