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Re: [Qemu-devel] buffer alignment for block backends

From: Gerd Hoffmann
Subject: Re: [Qemu-devel] buffer alignment for block backends
Date: Thu, 09 Apr 2009 15:54:34 +0200
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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?

The xen block protocol can handle unaligned requests just fine. The granted page is splitted into 512 sectors (8 pieces in case of 4k pages on x86). You can then request only some of the of the sectors being transfered. If you have two sectors with a 1024 byte offset to the page border you'll just ask for sectors 2+3.


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