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    SubjectRe: virtio scsi host draft specification, v3
    On 06/14/2011 10:39 AM, Hannes Reinecke wrote:
    > If, however, we decide to expose some details about the backend, we
    > could be using the values from the backend directly.
    > EG we could be forwarding the SCSI target port identifier here
    > (if backed by real hardware) or creating our own SAS-type
    > identifier when backed by qemu block. Then we could just query
    > the backend via a new command on the controlq
    > (eg 'list target ports') and wouldn't have to worry about any protocol
    > specific details here.

    Besides the controlq command, which I can certainly add, this is
    actually quite similar to what I had in mind (though my plan likely
    would not have worked because I was expecting hierarchical LUNs used
    uniformly). So, "list target ports" would return a set of LUN values to
    which you can send REPORT LUNS, or something like that? I suppose that
    if you're using real hardware as the backing storage the in-kernel
    target can provide that.

    For the QEMU backend I'd keep hierarchical LUNs, though of course one
    could add a FC or SAS bus to QEMU, each implementing its own identifier

    If I understand it correctly, it should remain possible to use a single
    host for both pass-through and emulated targets.

    Would you draft the command structure, so I can incorporate it into the

    > Of course, when doing so we would be lose the ability to freely remap
    > LUNs. But then remapping LUNs doesn't gain you much imho.
    > Plus you could always use qemu block backend here if you want
    > to hide the details.

    And you could always use the QEMU block backend with scsi-generic if you
    want to remap LUNs, instead of true passthrough via the kernel target.


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