Re: [PATCH 0/2] virtio-scsi: Implement FC_HOST feature

[Paolo Bonzini <pbonzini@redhat.com>]

> How it this supposed to work?
> You do export the WWPN/WWNN of the associated host to the guest (nb:
> will get interesting for non NPIV setups ...), but virtio scsi will
> still do a LUN remapping.
> IE the LUNs you see on the host will be different from the LUNs
> presented to the guest.

This is taken care of in the host by presenting to the host all LUNs from
a host's NPIV vHBA.  (Libvirt probably would be the one taking care of this,
because QEMU may not have enough permissions).

> Plus you don't _actually_ expose the FC host, but rather the WWPN of the
> host presenting the LUN.
> So how do you handle LUNs from different FC hosts on the guest?

I'm not sure I understand.

Neither I nor Fam know this stuff very well, but we are trying to do the same
as Hyper-V (and other proprietary hypervisors too).

> Overall, I'm not overly happy with this approach.
> You already added WWPN ids to the virtio transport, so why didn't you
> update the LUN field, too, to avoid this ominous LUN remapping?

Is this your old idea of adding a separate target field to commands,
in order to support 64-bit LUNs?  That is separate, and most FC drivers
only default to 16-bit LUNs anyway.

> And we really should make sure to have a single FC host in the guest
> presenting all LUNs.

Yes, of course.

Paolo