linux-kernel - Re: [RFC] Unify KVM kernel-space and user-space code into a single project

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Message-ID: <4BA7B9E0.5080009@codemonkey.ws>
Date:	Mon, 22 Mar 2010 13:41:36 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Avi Kivity <avi@...hat.com>, Pekka Enberg <penberg@...helsinki.fi>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	oerg Roedel <joro@...tes.org>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>, ziteng.huang@...el.com,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Fr?d?ric Weisbecker <fweisbec@...il.com>,
	Gregory Haskins <ghaskins@...ell.com>
Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single
 project

On 03/22/2010 12:34 PM, Ingo Molnar wrote:
> This is really just the much-discredited microkernel approach for keeping
> global enumeration data that should be kept by the kernel ...
>
> Lets look at the ${HOME}/.qemu/qmp/ enumeration method suggested by Anthony.
> There's numerous ways that this can break:
>
>   - Those special files can get corrupted, mis-setup, get out of sync, or can
>     be hard to discover.
>
>   - The ${HOME}/.qemu/qmp/ solution suggested by Anthony has a very obvious
>     design flaw: it is per user. When i'm root i'd like to query _all_ current
>     guest images, not just the ones started by root. A system might not even
>     have a notion of '${HOME}'.
>
>   - Apps might start KVM vcpu instances without adhering to the
>     ${HOME}/.qemu/qmp/ access method.
>
>   - There is no guarantee for the Qemu process to reply to a request - while
>     the kernel can always guarantee an enumeration result. I dont want 'perf
>     kvm' to hang or misbehave just because Qemu has hung.
>    

If your position basically boils down to, we can't trust userspace and 
we can always trust the kernel, I want to eliminate any userspace path, 
then I can't really help you out.

I believe we can come up with an infrastructure that satisfies your 
actual requirements within qemu but if you're also insisting upon the 
above implementation detail then there's nothing I can do.

Regards,

Anthony Liguori

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