linux-kernel - Re: [PATCH v2 01/11] scsi: Convert struct Scsi_Host->cmd_serial_number to atomic

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Date:	Sat, 18 Sep 2010 12:57:58 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Mike Christie <michaelc@...wisc.edu>
Cc:	Joe Eykholt <jeykholt@...co.com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Vasu Dev <vasu.dev@...ux.intel.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	James Bottomley <James.Bottomley@...e.de>,
	James Smart <james.smart@...lex.com>,
	Andrew Vasquez <andrew.vasquez@...gic.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Hannes Reinecke <hare@...e.de>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 01/11] scsi: Convert struct
	Scsi_Host->cmd_serial_number to atomic_t

On Fri, 2010-09-17 at 21:45 -0500, Mike Christie wrote:
> On 09/17/2010 02:03 PM, Joe Eykholt wrote:
> >
> > How about instead of adding use_serial_number, let's just have the
> > drivers that want a serial number call scsi_cmd_get_serial()
> 
> I think this sounds better.
> 

In that case I will go ahead and add explict scsi_cmd_get_serial() calls
to the LLDs that use struct scsi_cmnd->serial_number in anything beyond
an obvious and simple informational purpose.

> You could also convert drivers to the host tagging if you needed a 
> unique id for each command sent to a host.

Hmmm, what does this entail again..?

> 
> > and stop calling it from scsi_dispatch_cmd()?   AFAICT, it's only
> > used in debug messages in some drivers.  I didn't find other usages
> > but didn't do an exhaustive search.
> 
> The comments for serial_number say that it is only supposed to be used 
> for debugging printks and most drivers use it for that.

So I would suppose it would be OK for those drivers to continue to
printk serial_number to show the internal serial_number allocation is
now disabled by default.

> However, it looks like mpt and dpt_i2o are using it for error handling
> and/or lookup type of operations. I think the mpt* uses are not needed
> in the abort checks.
> 

In that case, then adding an explict scsi_cmd_get_serial() call in mpt*
and dpt_i20 ->queuecommand() callers would be a good first step.

> And eata is using it for ordering and tracking or something. It could 
> probably be converted to the host tagging if or what you suggested if it 
> needs the uniqueue id.

Adding an explict scsi_cmd_get_serial() for eata for now, and we can
consider LLD canidates for host tag conversion as a future step.

> 
> zfcp looks like it copies it. It does not look like the driver needs it.
> 

Ok, I will look at removing it's usage in zfcp or if necessary add an
the explict scsi_cmd_get_serial() call.

> scsi_error.c uses it in scsi_try_to_abort_cmd to check if a command has 
> completed, but I think that can be done by checking if REQ_ATOM_COMPLETE 
> is set.

Hmmm, good catch here.  Jejb and hch, does this item work for you..?

If so then I will take another peek for any ML uses of a struct
scsi_cmnd->serial_number that need to be addressed, and include Joe's
and Mike's recommendations into a v3 series.

Thanks for your comments here Mike!

--nab

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