Re: [Qemu-devel] [RFC PATCH 0/6] SCSI series part 2, rewrite LUN parsing

[Paolo Bonzini]

On 05/25/2011 03:17 PM, Christoph Hellwig wrote:
> On Fri, May 20, 2011 at 07:37:30PM +0200, Paolo Bonzini wrote:
> > On 05/20/2011 06:14 PM, Christoph Hellwig wrote:
> > > I don't quite understand what you mean with path here.  It doesn't
> > > seem to map to any SAM concept, nor does it seem to be related
> > > to traditional multipathing.
> >
> > It's what SAM calls a "bus identifier" in the description of LUN addressing
> > modes.
>
> Ok, so it more or less translates to the concept of a "channel" in
> the Linux SCSI subsystem.

Yes.

> It would help if you could explain the concept
> in a bit more detail in a comment.  Or in fact not bother with it at all,
> which should be easy if we never present hierachial LUNs.

Unfortunately spapr_vscsi requires hierarchical LUNs.  The OpenFirmware 
code starts by sending out INQUIRY messages to channel 0/1/2/3/4/5/6/7 
target 0 LUN 0 (it doesn't recognize other targets or LUNs as far as I 
can see).  So if you want to have a CD-ROM and a HD on your virtual 
machine, and you want your HD to keep its name both during the 
installation process and afterwards, you pretty much have to use channel 
0 for the HD and another channel for the CD-ROM..

Paolo