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Date: Thu, 09 Apr 2009 16:46:38 +0100
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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Subject: Re: [Qemu-devel] buffer alignment for block backends
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To: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

Samuel Thibault wrote:

> Gerd Hoffmann, le Thu 09 Apr 2009 15:54:34 +0200, a écrit :
>> On 04/09/09 15:30, Stefano Stabellini wrote:
>>> The userspace\kernelspace distinction does not make much sense in
>>> minios, but yes it provides an interface to communicate with blkback in
>>> dom0. This interface is used by block-vbd in qemu instead of
>>> block-raw-posix when run in minios.
>> Sit back, look again.  Do you really need it being page-aligned?
> 
> Page aligned is an optimization which comes for free when you can
> already choose the alignment.
> 
>> The xen block protocol can handle unaligned requests just fine.
> 
> Not completely arbitrarily aligned requests. They need to be
> sector-aligned.
> 

Samuel is right, I was misled by my test environment.
Blkfront does support sector aligned buffers (even though at the moment
they don't work for me :P ).