Re: [PATCH] minimal SAS transport class

[Jeff Garzik <jgarzik@pobox.com>]

Luben Tuikov wrote:
> On 08/26/05 13:22, James Bottomley wrote:
> 
>>On Fri, 2005-08-26 at 12:43 -0400, Luben Tuikov wrote:
>>
>>
>>>>A move away from forced HCIL addressing would be a good thing.
>>>>
>>>>However, its impossible to completely move away from addressing, as 
>>>>userspace and the SCSI core need ways to route CDBs to devices based on 
>>>>address.
>>>
>>>They can use _anyone_ label in the label list of the LU.
>>
>>
>>I think what Jeff means is that the mid-layer needs to know which LLD to
>>send the CDB to.
> 
> 
> No, I thought he meant about user space apps, *NOT* SCSI Core.
> 
> Since, the transport found the device on the domain (NOT LU!)
> it then calls SCSI Core to register it.
> 
> So you have:
> 
> task->scsi_domain_device->lldd->lldd_execute_task(task).
> 
> 
>>This is the routing information (and is really just
>>the host number).
> 
> 
> No host numbers, no routing information.  This is all
> transparent to SCSI Core, and NONE of its business.


Routing is an essential part of the SCSI core's duties.

The SCSI core is the resource manager responsible for routing messages 
[CDBs] to/from LLDs based on <scsi-specific device address>.  This 
includes resolution of kernel-specific identifiers (device major/minor, 
etc.) into <s.s.d.a.>.  This also includes direct use of 
userspace-provided identifiers as <s.s.d.a.>, such as via SG_IO ioctl.

Moving away from HCIL requires a lot of thought, including thinking 
about userland app breakage -- a big deal in Linux.

Ask yourself where all these HCIL-addressed CDBs come from...  each one 
of those CDB submittors must be updated from HCIL addressing/routing to 
transport-specific.

	Jeff