Re: [PATCH scsi-misc-2.6 01/08] scsi: remove unused bounce-buffer release path

[Tejun Heo <htejun@gmail.com>]

 Hello, James.

James Bottomley wrote:
> On Wed, 2005-03-23 at 11:14 +0900, Tejun Heo wrote:
>
> > 01_scsi_remove_scsi_release_buffers.patch
> >
> > 	Buffer bouncing hasn't been done inside the scsi midlayer for
> > 	quite sometime now, but bounce-buffer release paths are still
> > 	around.  This patch removes these unused paths.
>
>
> Yes, but scsi_release_buffers isn't referring to bounce buffers anymore,
> it's simply releasing the sg buffers.

 That's what I did.  Replacing scsi_release_buffers() calls with calls 
to scsi_free_sgtable().  The only logic removed is bounce-buffer 
release/copy-back.

> [...]
>
> > -	else if (cmd->buffer != req->buffer) {
> > -		if (rq_data_dir(req) == READ) {
> > -			unsigned long flags;
> > -			char *to = bio_kmap_irq(req->bio, &flags);
> > -			memcpy(to, cmd->buffer, cmd->bufflen);
> > -			bio_kunmap_irq(to, &flags);
> > -		}
> > -		kfree(cmd->buffer);
> > -	}
>
>
> I'll defer to Jens here, but I don't thing you can just remove this ...
> sg_io with a misaligned buffer will fail without this.

 AFAIK, those are done by blk_rq_map_user() and blk_rq_unmap_user(), 
both of which are invoked directly by sg_io().

> That rather nasty code freeing cmd->buffer needs to be in there as
> well ... so it does make sense to keep this API

 That code is invoked only for REQ_BLOCK_PC requests without bio, and I 
digged pretty hard but, in those cases, AFAICT, the callers are 
responsible for supplying dma-able buffers and nothing seems to alter 
cmd->buffer after the cmd gets initialized, but I might be missing 
things here.  If so, please point out.

 Thanks.

--
tejun

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