linux-kernel - Re: [PATCH 0/2] virtio-scsi: Implement FC

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Date:   Mon, 16 Jan 2017 15:17:59 -0500 (EST)
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Hannes Reinecke <hare@...e.de>
Cc:     Fam Zheng <famz@...hat.com>, linux-kernel@...r.kernel.org,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        virtualization@...ts.linux-foundation.org, stefanha@...hat.com
Subject: Re: [PATCH 0/2] virtio-scsi: Implement FC_HOST feature


> 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