[libvirt] [PATCH 0/2] Alter refresh algorithm for volWipe

[Martin Kletzander]

On Fri, Aug 25, 2017 at 07:52:25AM -0400, John Ferlan wrote:
>
>
>On 08/25/2017 05:44 AM, Martin Kletzander wrote:
>> On Thu, Aug 24, 2017 at 06:28:27PM -0400, John Ferlan wrote:
>>> Alter wipeVol to do same refresh operation as pool refresh would do.
>>>
>>
>> I think we should rather keep the format as it is.  Did I miss something
>> here or isn't the source of the problem just the fact that we wipe the
>> volume without keeping the format?
>>
>
>Once you "wipe" the file/image the format that was there (such as qcow2
>as noted in the bz from patch2) is no longer there.
>
>Consider the following sequence:
>
>virsh vol-create-as default bz 10M --format qcow2
>
>virsh vol-dumpxml bz default | grep format
>    <format type='qcow2'/>
>
>qemu-img info /home/vm-images/bz
>image: /home/vm-images/bz
>file format: qcow2
>virtual size: 10M (10485760 bytes)
>disk size: 196K
>cluster_size: 65536
>Format specific information:
>    compat: 0.10
>    refcount bits: 16
>
>virsh vol-wipe bz default
>
>qemu-img info /home/vm-images/bz
>image: /home/vm-images/bz
>file format: raw
>virtual size: 196K (200704 bytes)
>disk size: 196K
>
>virsh vol-dumpxml bz default | grep format
>    <format type='qcow2'/>
>
>(without the patch in 2/2 of course)
>
>BTW: I did consider just changing the format to RAW regardless, but
>figured that was just too simple and may not be the right answer for
>every case.
>

Sure, but that's not my point.  My point is that instead of rewriting
the data with zeros, we could re-initialize it.  Anyway, from what I see
in the docs, we "fixed" it by documenting this behaviour already, so my
point is moo:

https://libvirt.org/html/libvirt-libvirt-storage.html#virStorageVolWipe

(I guess I should know that when I pushed that documentation into the tree)

So ACK series.
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