libvirt users - Aug 2014 - Re: Does libvirt have API to detect image format

>
I am using backing store when I create my volume. However, the backing
store file is from another team, which can be either in raw or in qcow2
format.

Is there a libvirt API to detect image format by given an image file? Or I
have to run qemu-img?

>

On 08/11/2014 02:35 PM, Jianfeng Tang wrote:
>>
> 
> I am using backing store when I create my volume. However, the backing
> store file is from another team, which can be either in raw or in qcow2
> format.
> 
> Is there a libvirt API to detect image format by given an image file? Or I
> have to run qemu-img?
virStorageVolGetXMLDesc() in the C code ('virsh vol-dumpxml' from the
command line), if your volume resides within a storage pool.
Furthermore, if there is ANY possibility that the file might be raw but
that the volume has been in use by a possibly malicious guest, you
CANNOT blindly trust a file probe that says qcow2, because a guest can
write header information into a raw disk in order to make probes return
qcow2.  So take the output with a grain of salt (it is safe to blindly
trust a claim of 'raw', but blindly trusting a claim of 'qcow2'
is risky
if you don't know the history behind the image).

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

Unfortunately my backing store file is not in a volume. So I guess I
cannot use that method.

On 8/11/14 3:45 PM, "Eric Blake" <eblake@redhat.com> wrote:
>On 08/11/2014 02:35 PM, Jianfeng Tang wrote:
>>>
>> 
>> I am using backing store when I create my volume. However, the backing
>> store file is from another team, which can be either in raw or in qcow2
>> format.
>> 
>> Is there a libvirt API to detect image format by given an image file?
>>Or I
>> have to run qemu-img?
>
>virStorageVolGetXMLDesc() in the C code ('virsh vol-dumpxml' from
the
>command line), if your volume resides within a storage pool.
>Furthermore, if there is ANY possibility that the file might be raw but
>that the volume has been in use by a possibly malicious guest, you
>CANNOT blindly trust a file probe that says qcow2, because a guest can
>write header information into a raw disk in order to make probes return
>qcow2.  So take the output with a grain of salt (it is safe to blindly
>trust a claim of 'raw', but blindly trusting a claim of
'qcow2' is risky
>if you don't know the history behind the image).
>
>-- 
>Eric Blake   eblake redhat com    +1-919-301-3266
>Libvirt virtualization library http://libvirt.org
>

On Mon, Aug 11, 2014 at 08:35:46PM +0000, Jianfeng Tang
wrote:
> >
> 
> I am using backing store when I create my volume. However, the backing
> store file is from another team, which can be either in raw or in qcow2
> format.
> 
> Is there a libvirt API to detect image format by given an image file? Or I
> have to run qemu-img?
Nothing wrong with running `qemu-img info' IMHO.

Libguestfs has some disk detection features, including format, backing
file, virtual size.  And of course it can go a lot deeper into the
disk content itself using libguestfs inspection.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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