[libvirt] [PATCH] libvirt no longer supports qemu format=host_device

Jamie Strandboge jamie at canonical.com
Mon Nov 8 18:08:26 UTC 2010

On Mon, 2010-11-08 at 10:02 +0000, Daniel P. Berrange wrote:
> On Fri, Nov 05, 2010 at 02:04:50PM -0500, Jamie Strandboge wrote:> 
> > This is confirmed as not working on 0.8.3 and 0.8.5. The attached patch
> > against 0.8.5 fixes the issue and restores host_device support.
> host_device is not a data format type, but rather a qemu driver protocol.
> As such it is not applicable for the <driver type=XXX> field, because
> the protocol is already specified at the <disk> element level with
> a combo of the type+device fields. If it happened to be possible to
> set it in the <driver>  field that is just pure chance & not something
> that is supported. If we need to setup host_device anywhere, then this
> needs to be dealt with at the qemu_conf.c where we generate the CLI
> args.  

Hmm... that is not clear in the documention IMHO (and the patch was
careful to only use this for the qemu driver). Eg from the qemu-img man

"Supported image file formats:
    raw ...
    host_device ...
    qcow2 ...

Ie, the language in the qemu-img man page has 'host_device' at the same
level as 'raw', 'qcow2', 'cow', etc as a 'file format'.
http://libvirt.org/formatdomain.html#elementsDisks only talks about a
'sub-type' for the qemu driver (but it is easy to infer that it is
looking at the qemu-img types after using libvirt for a while) and
http://libvirt.org/storage.html does not list 'host_device' as a 'format
type', but it does list all of the other ones from the same section of
the qemu-img man page (except 'vdi', which is maybe an omission in the
libvirt docs?). Finally, 'man virsh' does list 'host_device' as a 'file
format' in its 'vol-create-as' command.

By all means if this needs to be cleaned up in qemu_conf.c that seems
fine, but until then I feel that either host_device should be supported
again (preferred based on the qemu-img man page) or the documentation
made more consistent, and something probably added in
http://libvirt.org/news.html for people upgrading to 0.8.3 or later
since libvirt users are hitting this.

Jamie Strandboge             | http://www.canonical.com
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