Re: [RFC] [PATCH] qla4xxx driver resubmission

[James Smart <James.Smart@Emulex.Com>]

David Somayajulu wrote:
>> Why does your LLD need to reach up into the block layer to find an i/o
> ?
> Block layer tagging was the gating item in the previous submission.
> Going over the conversation on the linux-scsi reflector on STEX driver
> in this aspect, led us to believe that there should not be any driver
> level book-keeping of outstanding commands to the HBA. This was the
> reason for creating scsi_host_find_tag() in scsi_tcq.h (in the patch
> titled [RFC] [PATCH] helper function for retrieving scsi_cmd given
> hostbased block layer tag)
> http://marc.theaimsgroup.com/?l=linux-scsi&m=115871027627964&w=2
> 
> James, would you mind letting us know if block-layer tagging in your
> opinion simply meant using the scsi_cmd->request->tag and let the driver
> do the book-keeping of out-standing commands to HBA (like stex driver)
> or is it along the lines we have implemented.

Well, in general, I've been working on stuff that has little use for the
tags, so they aren't that meaningful. I can certainly see some implementations
that can benefit.

But, on a newish transport like iSCSI, I'm surprised. There's lots of
house-keeping that has to be done with resets and task management that makes
me believe it's better/easier with local structures. I also know that I like
to double-check my hardware (based on local structure) rather than blindly
trusting job handles. I also believe there will be locking issues or data
structures in flight issues between the block layer and LLDD that will
be ugly.

I wanted some justification. The new block layer function hasn't been needed
in the past and I thought it a rather odd thing to add.

-- james