Re: [PATCH 1/3] block: Introduce __blk_segment_map_sg() helper

[Asias He]

On 06/19/2012 05:31 AM, Tejun Heo wrote:
> Hello, Asias.
>
> On Mon, Jun 18, 2012 at 02:53:08PM +0800, Asias He wrote:
> > Split the mapping code in blk_rq_map_sg() to a helper
> > __blk_segment_map_sg(), so that other mapping function, e.g.
> > blk_bio_map_sg(), can share the code.
> >
> > Cc: Jens Axboe <axboe@xxxxxxxxx>
> > Cc: Tejun Heo <tj@xxxxxxxxxx>
> > Cc: Shaohua Li <shli@xxxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Suggested-by: Tejun Heo <tj@xxxxxxxxxx>
> > Suggested-by: Jens Axboe <axboe@xxxxxxxxx>
> > Signed-off-by: Asias He <asias@xxxxxxxxxx>
> > ---
> >   block/blk-merge.c |   80 ++++++++++++++++++++++++++++++-----------------------
> >   1 file changed, 45 insertions(+), 35 deletions(-)
> >
> > diff --git a/block/blk-merge.c b/block/blk-merge.c
> > index 160035f..576b68e 100644
> > --- a/block/blk-merge.c
> > +++ b/block/blk-merge.c
> > @@ -110,6 +110,49 @@ static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
> >   	return 0;
> >   }
> >
> > +static void
> > +__blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
> > +		     struct scatterlist *sglist, struct bio_vec **bvprv,
> > +		     struct scatterlist **sg, int *nsegs, int *cluster)
> > +{
> > +
> > +	int nbytes = bvec->bv_len;
> > +
> > +	if (*bvprv && *cluster) {
> > +		if ((*sg)->length + nbytes > queue_max_segment_size(q))
> > +			goto new_segment;
> > +
> > +		if (!BIOVEC_PHYS_MERGEABLE(*bvprv, bvec))
> > +			goto new_segment;
> > +		if (!BIOVEC_SEG_BOUNDARY(q, *bvprv, bvec))
> > +			goto new_segment;
> > +
> > +		(*sg)->length += nbytes;
> > +	} else {
> > +new_segment:
> > +		if (!*sg)
> > +			*sg = sglist;
> > +		else {
> > +			/*
> > +			 * If the driver previously mapped a shorter
> > +			 * list, we could see a termination bit
> > +			 * prematurely unless it fully inits the sg
> > +			 * table on each mapping. We KNOW that there
> > +			 * must be more entries here or the driver
> > +			 * would be buggy, so force clear the
> > +			 * termination bit to avoid doing a full
> > +			 * sg_init_table() in drivers for each command.
> > +			 */
> > +			(*sg)->page_link &= ~0x02;
> > +			*sg = sg_next(*sg);
> > +		}
> > +
> > +		sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
> > +		(*nsegs)++;
> > +	}
> > +	*bvprv = bvec;
> > +}
>
> I *hope* this is a bit prettier.  e.g. Do we really need to pass in
> @sglist and keep using "goto new_segment"?

I think this deserves another patch on top of this splitting one. I'd 
like to clean this up later.

--
Asias


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/