Re: [Qemu-ppc] Bug with REPORT LUNS in IBM VSCSI

[Nathan Whitehorn]

On 10/04/13 04:55, Nikunj A Dadhania wrote:
> Nathan Whitehorn <address@hidden> writes:
>
> > On 10/02/13 10:17, Paolo Bonzini wrote:
> > > Il 02/10/2013 17:12, Nathan Whitehorn ha scritto:
> > > > I'm having some trouble with the VSCSI emulation in the pSeries machine.
> > > > It seems that the emulated SCSI target device on the SRP IT_nexus
> > > > properly distributes SCSI commands to its children but does not report
> > > > them in response to a REPORT LUNS request. This happens because it
> > > > forwards REPORT LUNs to target 0 on its child bus instead of answering
> > > > the command itself.
> > > How so?  The SCSI emulation hijacks REPORT_LUNS and does not pass it
> > > down to the device's alloc_req callback, but the request is still
> > > processed as if it came to the device.
> > >
> > > Can you give QEMU's command-line?  Can you reproduce the same bug with
> > > an x86 FreeBSD guest using virtio-scsi?
> > The issue is that VSCSI SRP has only one direct target port and then
> > uses hierarchical LUNs to pass requests further down the bus using the
> > LUN addressing method. My understanding of SAM5 is that the emulated
> > target device should report all of those sub-LUNs, on all sub-targets,
> > in response to a REPORT LUNS command addressed to LUN 0 on the only
> > direct target. Is that correct?
> What I see in slof code wrt the above in board-qemu/slof/vio-vscsi.fs:
>
>
> \ We use SRP luns of the form 8000 | (bus << 8) | (id << 5) | lun
> \ in the top 16 bits of the 64-bit LUN
>
> Thats the reason I suppose you would not find anything at 0.

Zero is also a legitimate choice (and works). Per the SRP and SCSI 
standards, all other LUNs are supposed to be reported by a REPORT LUNs 
to LUN zero or the "REPORT LUNs" well-known LUN -- SRP doesn't have any 
concept of "bus" and "id". QEMU's emulation seems to violate the 
standard in this respect, however. I don't have any actual pSeries 
hardware handy at the moment, but I would assume that it does do REPORT 
LUNs correctly given the Linux VSCSI target code I have seen.
-Nathan