Re: Proposals to change the way all drivers work with SCSI commands

[Muli Ben-Yehuda <muli@il.ibm.com>]

On Fri, May 11, 2007 at 01:33:41PM -0500, James Bottomley wrote:
> Right at the moment, we're planning to clean up the way SCSI drivers
> process commands.  The proposals are essentially:
> 
>      1. Get rid of the now unnecessary map_single path (every command is
>         either zero transfer or scatter/gather)
>      2. use accessors to manipulate the SG lists (mainly so that we can
>         alter the implementation without affecting the drivers)
> 
> It strikes me that in all of this, we could also consider doing the DMA
> mapping inside the mid layer (instead of in every driver).  This is
> essentially what libata is already doing ... leading to confusion in
> SCSI drivers that use libata for SATA.
> 
> So what do people think about this?

Yes please. It will be easier to modify the DMA API interface to
better support hypervisors and other "DMA mapping heavy" users if it's
localized to the mid-layer rather than spread out in drivers.

Cheers,
Muli