Re: [Fwd: [RFT] major libata update]

[Jeff Garzik <jeff@garzik.org>]

James Bottomley wrote:
> On Wed, 2006-05-17 at 11:06 -0400, Jeff Garzik wrote:
>> storage device and storage host are key objects included in the 
> 
> This is one of the questions.  Currently block has no concept of "host".
> All it knows about are queues (which may be per host or per device
> depending on the implementation).  Do we need to introduce the concept
> of something like queue grouping (a sort of lightweight infrastructure
> that could be used by the underlying transport to implement a host
> concept without introducing hosts at the block layer)?

Yes, and not only that...  you must describe the queue pipeline too. 
i.e. N logical devices can be bottlenecked behind a bridge (expander, 
port multiplier, tunnel) of queue depth Q, which may in turn be behind 
another bottleneck.  :)

But overall, libata and SAS controllers are forced to deal with the 
reality of the situation:  they all wind up either using, or recreating 
from scratch, objects for host/device/bus/etc. in order to sanely allow 
all the infrastructure to interoperate.

You'll all note that struct Scsi_Host and struct scsi_cmnd have very 
little to do with SCSI.  Its almost all infrastructure and driver 
management.  That's the _useful_ stuff that libata uses SCSI for.

Thus, moving libata to the block layer entails either 
s/Scsi_Host/Storage_Host/g or a highly similar infrastructure, to 
achieve the same gains.

It is _trivial_ to write a new SCSI driver [even if your hardware is not 
SCSI], and there are good reasons for that.  Please all, examine those 
reasons...

	Jeff