[Libguestfs] [PATCH] v2v: add support for virtio-scsi

[Richard W.M. Jones]

On Wed, Apr 13, 2016 at 07:45:42PM +0300, Roman Kagan wrote:
> On Wed, Apr 13, 2016 at 10:11:54AM +0100, Richard W.M. Jones wrote:
> > On Tue, Apr 12, 2016 at 06:46:31PM +0300, Roman Kagan wrote:
> > > +  (* Presence of virtio-scsi controller. *)
> > > +  let has_virtio_scsi =
> > > +    let obj = Xml.xpath_eval_expression xpathctx
> > > +                "/domain/devices/controller[@model='virtio-scsi']" in
> > 
> > I guess this short cut is OK.  A true test would involve checking the
> > <target bus="scsi"> on each disk and matching it back to the
> > controller.  In other words, a huge pain!  Maybe you can add an "XXX"
> > comment in the source about this.
> 
> On a second look, I'm not sure I got your comment right.
> 
> AFAICS there's no way in libvirt xml to define multiple scsi buses,

I think this is possible, although massively unlikely in practice.  I
think the different controllers would have different
index="0"/index="1"/... attributes.

> so all the matching I can do is just to notice the presence of
> virtio-scsi controller, and attribute all SCSI drives to it.  This
> is exactly what happens in the patch.
>
> Am I missing something?

So first off I think this part of the patch and your assumption is
fine, there's no need to change the code.

However there is a possibility that the source guest might have
multiple mixed virtio-blk + virtio-scsi disks.  In that case the disks
would look like this:

    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file=...>
      <target dev='vda' bus='virtio'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file=...>
      <target dev='sda' bus='scsi'/>
    </disk>
    <controller type="scsi" index="0" model="virtio-scsi"/>

It's not something that we should worry about, and a simple comment
with "XXX" in it is fine, if you agree with my analysis.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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