Re: [PATCH] virtio-scsi: define VIRTIO_SCSI_F_FC_HOST

[Stefan Hajnoczi <stefanha@redhat.com>]

On Wed, Nov 30, 2016 at 01:08:44PM +0100, Paolo Bonzini wrote:
> 
> 
> On 30/11/2016 11:43, Stefan Hajnoczi wrote:
> > On Tue, Nov 29, 2016 at 02:56:07PM +0100, Paolo Bonzini wrote:
> >> Add a new feature and the related configuration fields.
> >>
> >> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> >> ---
> >>  content.tex | 22 ++++++++++++++++++++++
> >>  1 file changed, 22 insertions(+)
> > 
> > Hi Paolo,
> > Can you elaborate a bit on how this feature can be used?
> > 
> > It's not clear to me why having exactly two addresses is useful rather
> > than having just one or allowing the inactive address to change.
> 
> Because the WWNN and WWPN in the virtio-scsi configuration must be used
> when creating the NPIV virtual HBA in the host, you do not want two
> hosts to use the same WWNN and WWPN.  That would be the same as using
> the same MAC address on two machines.  The switch from primary to
> secondary or vice versa then happens on migration.  This is the same
> scheme used by Hyper-V.

Ah, I see.  So each guest has not one but two assigned addresses and
only one of them is in use at any given time.  When doing multiple
migrations you keep flipping between the two allocated addresses.

It would be useful to describe the purpose in the spec.  The usage
wasn't obvious to me although it makes sense after you explained it.

Stefan

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