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

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Message-ID: <4509DC8F.6030900@garzik.org>
Date:	Thu, 14 Sep 2006 18:49:51 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	"Darrick J. Wong" <djwong@...ibm.com>
CC:	linux-ide <linux-ide@...r.kernel.org>,
	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>,
	James Bottomley <James.Bottomley@...elEye.com>
Subject: Re: [PATCH v3] libsas: move ATA bits into a separate module

Darrick J. Wong wrote:
> 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.

Looks MUCH better to me, and eliminates my objection to the 
libata-related hooks.

There remains the issue that I poke James about on IRC, namely that 
there is no need to emulate the SATA phy registers.  libata permits a 
driver high level access to the ATA engine without needing SATA SCRs. 
Witness all the PATA drivers, which obviously do not have SCRs at all.

	Jeff



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