linux-kernel - Re: [kvm-devel] [RFC] Stable kvm userspace interface

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Date:	Thu, 11 Jan 2007 09:40:57 -0800 (PST)
From:	David Lang <david.lang@...italinsight.com>
To:	Arnd Bergmann <arnd@...db.de>
cc:	kvm-devel@...ts.sourceforge.net, Jeff Garzik <jeff@...zik.org>,
	Avi Kivity <avi@...ranet.com>, Andrew Morton <akpm@...l.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [kvm-devel] [RFC] Stable kvm userspace interface

On Thu, 11 Jan 2007, Arnd Bergmann wrote:

> On Tuesday 09 January 2007 14:47, Jeff Garzik wrote:
>> Can we please avoid adding a ton of new ioctls?  ioctls inevitably
>> require 64-bit compat code for certain architectures, whereas
>> sysfs/procfs does not.
>
> For performance reasons, an ascii string based interface is not
> desireable here, some of these calls should be optimized to
> the point of counting cycles.

why is this? most of the API that is being discussed is run once when the VM is 
being setup.

there may be some calls that are performance sensitive, but for things like 
seperating the page tables, the cost of doing the work will swamp any ASCII 
conversion costs.

David Lang

> Sysfs also does not fit the use case at all, and procfs only
> makes sense if you really want to keep all information about the
> guest as part of the process directory it belongs to.
>
> I still think that in the long term, we should migrate to
> new system calls and a special file system for kvm, which
> might be non-mountable. Those will of course have the same
> 32 bit compat problems as the ioctl approach, but so far,
> Avi has kept a good watch on avoiding these problems.
>
> As long as we think the interface is likely to change (which it
> certainly is right now), I believe that ioctl is the right
> interface. We can think about retiring it when the interface has
> stabilized enough to be converted to syscalls.
>
> 	Arnd <><
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