Re: PMP and SEMB messages to SEP

[James Bottomley <James.Bottomley@suse.de>]

On Mon, 2011-01-17 at 18:18 +0100, Tejun Heo wrote:
> Hello, James.
> 
> On Mon, Jan 17, 2011 at 10:18:51AM -0600, James Bottomley wrote:
> > > The problem is that the PMP device itself is currently not allocated a
> > > userland visible device, so it doesn't have any /dev/* node.  Hmmm...
> > 
> > So perhaps it should be.  If you look at the equivalent topology on SAS,
> > our expanders have a bsg device node precisely so that we can do this.
> >
> > That said, SAS expanders have a defined protocol (SAS Management
> > Protocol) to talk to the outside world, so they are real visible objects
> > always in our topology ... I'm not sure PMP has this ... it seems that
> > all PMP visibility is an extension to the standard?
> 
> SATA PMP is mostly a dumb switch and there isn't much which can be
> done by issuing custom commands (and IIRC we didn't have bsg back
> then), so it was never made visible to userland, but yeah probably
> exporting a bsg node is a good idea.  Inside libata, the PMP device
> has its device representation and all so it shouldn't be too difficult
> either.  Not really sure how the inquiry and stuff should be handled
> tho.

Expanders aren't SCSI devices either ... that means they don't appear as
visible to standard SCSI mechanisms like INQUIRY (SMP isn't a SCSI
protocol it's a SAS extension).  They just appear as part of the
topology in the device tree.

James