Re: [RFC PATCH-mm] scsi: use unaligned endian helpers rather than byteshifting

[Matthew Wilcox <matthew@wil.cx>]

On Wed, Dec 03, 2008 at 11:37:23AM -0800, Harvey Harrison wrote:
> Depends on the unaligned access work in -mm.  Just so you can see what the
> transition would look like.  See in particular the READ/WRITE6 bits
> as just reading the full 32 bits and masking ends up being better on
> lots of arches. (x86/powerpc/SH at least)

>  		case WRITE_6:
>  		case READ_6:
> -			lba = ((scsicmd->cmnd[1] & 0x1F) << 16) |
> -			    (scsicmd->cmnd[2] << 8) | scsicmd->cmnd[3];
> +			lba = load_be32_noalign((__be32 *)&scsicmd->cmnd[0]) & 0x1fffff;
>  			break;

That may well generate better code, but I have a hard time convincing
myself that it's correct.  This badly needs to be abstracted into
something *THAT MAKES SENSE FOR SCSI*.

James, if I resend my patches that introduce scsi_get_u24() et al, will
you apply them?  I'm tired of having to nack all the crazy patches that
Harvey keeps sending.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."