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Date: Tue, 25 May 2010 08:17:13 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [RFC PATCH 1/1] ceph/rbd block driver for qemu-kvm
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To: Avi Kivity <avi@redhat.com>
Cc: kvm@vger.kernel.org, qemu-devel@nongnu.org, Blue Swirl <blauwirbel@gmail.com>, ceph-devel@vger.kernel.org, Christian Brunner <chb@muc.de>, MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>

On 05/25/2010 04:14 AM, Avi Kivity wrote:
> On 05/24/2010 10:38 PM, Anthony Liguori wrote:
>>
>>> - Building a plugin API seems a bit simpler to me, although I'm to
>>> sure if I'd get the
>>>    idea correctly:
>>>    The block layer has already some kind of api (.bdrv_file_open, 
>>> .bdrv_read). We
>>>    could simply compile the block-drivers as shared objects and 
>>> create a method
>>>    for loading the necessary modules at runtime.
>>
>> That approach would be a recipe for disaster.   We would have to 
>> introduce a new, reduced functionality block API that was supported 
>> for plugins.  Otherwise, the only way a plugin could keep up with our 
>> API changes would be if it was in tree which defeats the purpose of 
>> having plugins.
>
> We could guarantee API/ABI stability in a stable branch but not across 
> releases.

We have releases every six months.  There would be tons of block plugins 
that didn't work for random sets of releases.  That creates a lot of 
user confusion and unhappiness.

Regards,

Anthony Liguori