[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH] qcow2: Optimize the refcount-block overlap chec

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH] qcow2: Optimize the refcount-block overlap check
Date: Mon, 30 Jan 2017 12:27:44 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0

On 01/30/2017 10:34 AM, Alberto Garcia wrote:

> I don't think QEMU produces files where refcount_table[i] == 0 but
> refcount_table[i + 1] != 0. Do they even make sense?

I don't know if qemu can be directly coerced to create such an image,
but a third party tool can (and that probably includes qemu-io), and
such an image makes sense.  In particular, a refcount can be changed
from non-zero to zero during garbage collection when all clusters
covered by that refcount are no longer in use (perhaps because a
snapshot was deleted).

> In any case, my
> patch would cover those cases too, but this simplified version wouldn't.

Since an image can have holes in the refcount_table, it sounds like the
simplified version is not robust enough.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

Attachment: signature.asc
Description: OpenPGP digital signature

reply via email to

[Prev in Thread] Current Thread [Next in Thread]