linux-kernel - Re: [PATCH] ide-floppy: use scatterlists for pio transfers

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Date:	Wed, 6 Aug 2008 21:30:56 +0200
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
Cc:	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ide-floppy: use scatterlists for pio transfers

On Wed, Aug 06, 2008 at 06:05:00PM +0200, Bartlomiej Zolnierkiewicz wrote:
> 
> Hi,
> 
> On Tuesday 05 August 2008, Borislav Petkov wrote:
> > Hi Bart,
> > 
> > here's my first stab at using scatterlists in ide-floppy. I've adapted your
> > ide-scsi version to fit in here. The change here is that i use pc->b_count as
> > a sort-of completion counter to know when i'm at the end of the sg element and
> > be able to switch to the next/finish transfer. I've tested the patch with the
> > Iomega ZIP drive i have here - it works. We should do some more testing first
> > though, before sending it upstream.
> 
> [...]
> 
> > @@ -569,7 +577,7 @@ static void idefloppy_create_rw_cmd(idefloppy_floppy_t *floppy,
> >  	memcpy(rq->cmd, pc->c, 12);
> >  
> >  	pc->rq = rq;
> > -	pc->b_count = cmd == READ ? 0 : rq->bio->bi_size;
> > +	pc->b_count = 0;
> >  	if (rq->cmd_flags & REQ_RW)
> >  		pc->flags |= PC_FLAG_WRITING;
> >  	pc->buf = NULL;
> 
> Don't we also need to zero pc->b_count in idefloppy_blockpc_cmd()?
> 
> [ idefloppy_init_pc() clears whole pc so ->b_count assignment
>   to zero is not strictly necessary ]

We probably should and i should've probably hit that during testing and maybe
hit an OOPS along that path but we don't do REQ_TYPE_BLOCK_PC in ide-floppy
yet, as it appears, and since idefloppy_blockpc_cmd() is only called when
blk_pc_request(rq) that's why this one doesn't matter here. We should consider
it though when we convert to using BLOCK_PC type rq's.

-- 
Regards/Gruss,
    Boris.
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