Re: [PATCH / RFC] scsi_error handler update. (1/4)

[Doug Ledford <dledford@redhat.com>]

On Thu, Feb 13, 2003 at 01:55:15PM -0500, Luben Tuikov wrote:
> 	::same_target_siblings -- this shouldn't exist by design.

Yes!  That one most certainly should exist!  There are lots of operations 
in the scsi protocol that are target specific instead of lun specific and 
having a quick, cheap way of getting to all the luns on a single target is 
important (for example, on SPI, all device transfer negotiations are 
target specific, so when you negotiate a speed with target 0 lun 0, you 
have also negotiated the speed of target 0 lun 1, and getting to and 
setting the "I've already negotiated with this device" flag on all your 
luns should be quick and easy).  Now, there are really only a few places 
where this kind of target vs. lun view is important:

device_busy:  we need to know how many commands are active on a lun, and 
in some cases also on a target.  So this should really be 
"active_cmd_count_target" and "active_cmd_count_lun" to use Luben's 
preferred names.  The active_cmd_count_target would actually have to be a 
pointer to the single real counter while each scsi device would have an 
independant lun counter.  This makes single_lun devices simpler because we 
just check that active_cmd_count_target == 0 before queueing a command.

hostdata:  ideally this would be lldd_lun_data and lldd_target_data and 
each would be a pointer that the lldd could init during slave_alloc() 
time.  That way if a lldd cares about the difference between target and 
lun data structs, then it can put them in different areas and treat them 
appropriately.

Hmmm...those are the two most important items.  There may be others I'm 
forgetting.  But, take care of those two and you should then be able to 
eliminate the same_target_siblings without incurring a bad performance 
penalty on single_lun devices.

-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606