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Date: Mon, 26 Jul 2010 14:03:50 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [PATCH] move 'unsafe' to end of caching modes in help
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To: Avi Kivity <avi@redhat.com>
Cc: Bruce Rogers <brogers@novell.com>, Markus Armbruster <armbru@redhat.com>, qemu-devel@nongnu.org

On 07/26/2010 11:29 AM, Avi Kivity wrote:
>  On 07/26/2010 07:26 PM, Avi Kivity wrote:
>>
>>> The help output is *not* a supported interface. 
>>
>> There is no supported, usable interface for this.
>
> Well actually, libvirt could probe this by starting qemu with cache=x 
> for various x and seeing if it breaks.  But the milk has already been 
> spilled.

So we're stuck with supporting the help output as an interface 
forever?   Even with a capabilities system, what about old versions of 
libvirt?

At some point in time, old versions of libvirt are going to stop working 
with new versions of QEMU because the help output changes.  If libvirt 
switches to something more reliable (like versioning), then the gap is 
closed until there is a capabilities system.

There will be a breakage though and we shouldn't pretend that taking 
this patch does anything other than delay that breakage.

Regards,

Anthony Liguori