linux-kernel - Re: [tip:tools/kvm] kvm tools, qcow: Fix copy-on-write image corruption

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Date:	Fri, 22 Jul 2011 11:21:09 +0300 (EEST)
From:	Pekka Enberg <penberg@...nel.org>
To:	Kevin Wolf <kwolf@...hat.com>
cc:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	levinsasha928@...il.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org, kvm-devel <kvm@...r.kernel.org>
Subject: Re: [tip:tools/kvm] kvm tools, qcow: Fix copy-on-write image
 corruption

On Thu, 21 Jul 2011, Kevin Wolf wrote:
> Hm, I must have missed this patch on the KVM mailing list...

It wasn't on the list, sorry.

> You should also error out before creating a new L2 table as its refcount
> would have to be updated, too. On the other hand, the patch is a bit too
> restrictive, because it applies the check to qcow1 which doesn't even
> have a refcount table.

Oh, right, I broken QCOW1.

> I'm not sure if everyone is aware of it, so another hint: Now that you
> can't grow qcow2 any more, you might find it useful to use qemu-img
> create -f qcow2 -o preallocation=metadata, so that all clusters are
> already present and you don't get random failures.

Yup, I'm aware that you can't grow images anymore. The patch was meant as 
a stop-gap measure while I'm hacking on refcount table support.

 			Pekka
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