linux-kernel - Re: [PATCH v3] libsas: move ATA bits into a separate module

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Date:	Thu, 14 Sep 2006 15:40:55 -0700
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Jeff Garzik <jeff@...zik.org>,
	linux-ide <linux-ide@...r.kernel.org>
CC:	linux-scsi <linux-scsi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alexis Bruemmer <alexisb@...ibm.com>,
	Mike Anderson <andmike@...ibm.com>
Subject: Re: [PATCH v3] libsas: move ATA bits into a separate module

Jeff Garzik wrote:

> I disagree completely with this approach.
> 
> You don't need a table of hooks for the case where libata is disabled in
> .config.  Thus, it's only useful for the case where libsas is loaded as
> a module, but libata is not.

Indeed, I misunderstood what James Bottomley wanted, so I reworked the
patch.  It has the same functionality as before, but this module uses
the module loader/symbol resolver for all the functions in libata, and
allows libsas to (optionally) call into sas_ata with weak references by
pushing a table of the necessary function pointers into libsas at
sas_ata load time.  Thus, libsas doesn't need to load libata/sas_ata
unless it actually finds a SATA device.

> The libsas code should directly call libata functions.  If ATA support
> in libsas is disabled in .config, then those functions will never be
> called, thus never loaded the libata module.

I certainly can (and now do) call libata functions from sas_ata.
However, there are a few cases where libsas needs to call libata (ex.
sas_ioctl); for those cases, I think the function pointers are still
necessary because I don't want to make libsas require libata.  In any
case, if ATA support is disabled in .config, sata_is_dev always returns
0, so the dead-code eliminator should zap that out of libsas entirely.

As usual, thank you for any feedback that you have.

Link to version 3:
http://sweaglesw.net/~djwong/docs/sas-ata_3.patch

--D

Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
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