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

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Message-ID: <4E2935DD.20005@redhat.com>
Date:	Fri, 22 Jul 2011 10:33:33 +0200
From:	Kevin Wolf <kwolf@...hat.com>
To:	Pekka Enberg <penberg@...nel.org>
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

Am 22.07.2011 10:21, schrieb Pekka Enberg:
> 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.

Yeah, I was pretty sure you were aware of _that_, but maybe not everyone
knows that metadata preallocation exists.

Kevin
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