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Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format

From: Avi Kivity
Subject: Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format
Date: Fri, 10 Sep 2010 14:15:59 +0300
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 On 09/10/2010 12:01 AM, Christoph Hellwig wrote:
On Thu, Sep 09, 2010 at 09:24:26AM +0300, Avi Kivity wrote:
The other thing we can do is defragment the logical image, then
defragment the underlying file (if the filesystem supports it, issue the
appropriate ioctl, otherwise defragment to a new file which you write
What's what the defragmentation code does in a slightly optimized
fashion anyway - so if you want to do it from qemu just do it that
way.  Don't even bother calling the filesystem ioctls directly given
that they just implementa low-level helpers and the actual logic is
in the userspace side of the defragmentation tools.

Well, if we ask the kernel do to it, we gain any future optimizations as well. For example, if parts of the file are already defragmented, the kernel can avoid moving that data.

I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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