Re: [RFC] SAS domain layout for Linux sysfs

[Christoph Hellwig <hch@infradead.org>]

> sysfs and SAS discovery
> -----------------------
> It seems reasonable that sda should be visible in sysfs
> since the silicon in the HBA (for scsi0) knows about it.
> However the silicon for scsi1 knows about ex1 (and
> nothing beyond that). SAS defines the Serial Management
> Protocol (SMP) for the purpose of probing what (else) is
> connected to an expander. SMP is similar to a SCSI command
> set and SMP frames need to be sent via scsi1 to ex1.
> Note that ex1 is _not_ a SCSI device (it is
> part of the service delivery subsystem) and we have no
> representation currently for it in sysfs. [Fibre channel
> switches are architecturally similar to SAS expanders.]

Note that the current scsi code allows to create custom per-transport
objects below the target object.  We're using that in the fibre channel
transport class for the concept of remote ports.

> Once the SAS discovery algorithm has been run should we
> show its results in sysfs??

I think so, yes.  Similar to how we have all fibre channel remote ports
in sysfs, even if they are not scsi targets.