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Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single project
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From: Alexander Graf <agraf@suse.de>
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Date: Thu, 18 Mar 2010 10:24:37 +0100
Cc: Avi Kivity <avi@redhat.com>, Anthony Liguori <anthony@codemonkey.ws>,
       "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
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To: Ingo Molnar <mingo@elte.hu>
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On 18.03.2010, at 09:56, Ingo Molnar wrote:

> 
> * Avi Kivity <avi@redhat.com> wrote:
> 
>> On 03/17/2010 10:10 AM, Ingo Molnar wrote:
>>> 
>>>> It's about who owns the user interface.
>>>> 
>>>> If qemu owns the user interface, than we can satisfy this in a very 
>>>> simple way by adding a perf monitor command.  If we have to support third 
>>>> party tools, then it significantly complicates things.
>>> 
>>> Of course illogical modularization complicates things 'significantly'.
>> 
>> Who should own the user interface then?
> 
> If qemu was in tools/kvm/ then we wouldnt have such issues. A single patch (or 
> series of patches) could modify tools/kvm/, arch/x86/kvm/, virt/ and 
> tools/perf/.

It's not a 1:1 connection. There are more users of the KVM interface. To name a few I'm aware of:

- Mac-on-Linux (PPC)
- Dolphin (PPC)
- Xenner (x86)
- Kuli (s390)

Having a clear userspace interface is the only viable solution there. And if you're interested, look at my MOL enabling patch. It's less than 500 lines of code.

The kernel/userspace interface really isn't the difficult part. Getting device emulation working properly, easily and fast is.


Alex