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Re: [Xen-devel] The two image formats called qcow

To: Kevin Wolf <kwolf@xxxxxxx>
Subject: Re: [Xen-devel] The two image formats called qcow
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 26 Mar 2008 14:15:50 +0000
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Otavio Salvador <otavio@xxxxxxxxxxxxxxxx>
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On 26/3/08 14:07, "Kevin Wolf" <kwolf@xxxxxxx> wrote:

>> Can we really tack an 'extended header' into a public format like qcow?
> 
> I didn't introduce this, it was already there in tapdisk. I don't see a
> problem with it as the start of the L1 table is referenced in the normal
> qcow header. qemu-img sets this to something like 0x48 which is
> immediately after the header, tapdisk uses 0x1000 and gains some unused
> space for things like the extended header. This is compatible with the
> qcow implementation of qemu/ioemu.
> 
> On the other hand, I could simply strip that extended header (i.e.
> overwrite the magic with 0x0) after having fixed the image. Then it
> wouldn't be detected as broken on the next start as well.

Oh, I see. I think it's fine as it is then. Is there any reason not to paste
this fixup code into tapdisk too?

 -- Keir



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