Re: PMP and SEMB messages to SEP

[Tejun Heo <tj@kernel.org>]

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.

Thanks.

-- 
tejun