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

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Date:	Wed, 24 Mar 2010 14:53:10 +0100
From:	Alexander Graf <agraf@...e.de>
To:	Avi Kivity <avi@...hat.com>
Cc:	Joerg Roedel <joro@...tes.org>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Ingo Molnar <mingo@...e.hu>,
	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>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...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

Avi Kivity wrote:
> On 03/24/2010 02:50 PM, Joerg Roedel wrote:
>>
>>> You can always provide the kernel and module paths as command line
>>> parameters.  It just won't be transparently usable, but if you're using
>>> qemu from the command line, presumably you can live with that.
>>>      
>> I don't want the tool for myself only. A typical perf user expects that
>> it works transparent.
>>    
>
> A typical kvm user uses libvirt, so we can integrate it with that.
>
>>>> Could be easily done using notifier chains already in the kernel.
>>>> Probably implemented with much less than 100 lines of additional code.
>>>>        
>>> And a userspace interface for that.
>>>      
>> Not necessarily. The perf event is configured to measure systemwide kvm
>> by userspace. The kernel side of perf takes care that it stays
>> system-wide even with added vm instances. So in this case the consumer
>> for the notifier would be the perf kernel part. No userspace interface
>> required.
>>    
>
> Someone needs to know about the new guest to fetch its symbols.  Or do
> you want that part in the kernel too?


How about we add a virtio "guest file system access" device? The guest
would then expose its own file system using that device.

On the host side this would simply be a -virtioguestfs
unix:/tmp/guest.fs and you'd get a unix socket that gives you full
access to the guest file system by using commands. I envision something
like:

SEND: GET /proc/version
RECV: Linux version 2.6.27.37-0.1-default (geeko@...ldhost) (gcc version
4.3.2 [gcc-4_3-branch revision 141291] (SUSE Linux) ) #1 SMP 2009-10-15
14:56:58 +0200

Now all we need is integration in perf to enumerate virtual machines
based on libvirt. If you want to run qemu-kvm directly, just go with
--guestfs=/tmp/guest.fs and perf could fetch all required information
automatically.

This should solve all issues while staying 100% in user space, right?


Alex

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