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

[Paolo Bonzini <pbonzini@redhat.com>]

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.

> Can you explain what a path is supposed to be, and why it's called a "path"?

It's a SAM "BUS IDENTIFIER", but bus was too confusing with respect to 
qdev's BusState (which represents either a SAM bus identifier or 
target).  I think the term "path" comes from Windows, see for example
http://msdn.microsoft.com/en-us/library/ff564699%28v=vs.85%29.aspx:

   PathId [in, optional]

     Indicates the SCSI port or bus for the request. This parameter is
     optional.

... but I chose it because I found it also in SAM: "The BUS IDENTIFIER 
field identifies the bus or path that the SCSI device shall use to relay 
the received command or task management function".

I might also call it scsi-initiator which is consistent from the idea 
that it sits between two targets ports.

Paolo