Date:	Mon, 27 Sep 2010 16:05:51 +0200
From:	Christof Schmitt <christof.schmitt@...ibm.com>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc:	Mike Christie <michaelc@...wisc.edu>,
	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 Sat, Sep 18, 2010 at 12:57:58PM -0700, Nicholas A. Bellinger wrote:
> 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.

In zfcp, the serial_number is only accessed for writing it to debug
traces. With the change that the driver has to request the serial
number through use_serial_number, simply remove the serial number from
zfcp.

Thanks,

Christof

> 
> > 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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