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    SubjectRe: [PATCH 03/33] block: convert to using sg helpers
    On Mon, Jul 16 2007, Bartlomiej Zolnierkiewicz wrote:
    >
    > Hi,
    >
    > On Monday 16 July 2007, Jens Axboe wrote:
    > > Convert the main rq mapper (blk_rq_map_sg()) to the sg helper setup.
    > >
    > > Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
    > > ---
    > > block/ll_rw_blk.c | 19 ++++++++++++-------
    > > 1 files changed, 12 insertions(+), 7 deletions(-)
    > >
    > > diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
    > > index ef42bb2..ab71087 100644
    > > --- a/block/ll_rw_blk.c
    > > +++ b/block/ll_rw_blk.c
    > > @@ -30,6 +30,7 @@
    > > #include <linux/cpu.h>
    > > #include <linux/blktrace_api.h>
    > > #include <linux/fault-inject.h>
    > > +#include <linux/scatterlist.h>
    > >
    > > /*
    > > * for max sense size
    > > @@ -1307,9 +1308,11 @@ static int blk_hw_contig_segment(request_queue_t *q, struct bio *bio,
    > > * map a request to scatterlist, return number of sg entries setup. Caller
    > > * must make sure sg can hold rq->nr_phys_segments entries
    > > */
    > > -int blk_rq_map_sg(request_queue_t *q, struct request *rq, struct scatterlist *sg)
    > > +int blk_rq_map_sg(request_queue_t *q, struct request *rq,
    > > + struct scatterlist *sglist)
    > > {
    > > struct bio_vec *bvec, *bvprv;
    > > + struct scatterlist *next_sg, *sg;
    > > struct bio *bio;
    > > int nsegs, i, cluster;
    > >
    > > @@ -1320,6 +1323,7 @@ int blk_rq_map_sg(request_queue_t *q, struct request *rq, struct scatterlist *sg
    > > * for each bio in rq
    > > */
    > > bvprv = NULL;
    > > + sg = next_sg = &sglist[0];
    > > rq_for_each_bio(bio, rq) {
    > > /*
    > > * for each segment in bio
    > > @@ -1328,7 +1332,7 @@ int blk_rq_map_sg(request_queue_t *q, struct request *rq, struct scatterlist *sg
    > > int nbytes = bvec->bv_len;
    > >
    > > if (bvprv && cluster) {
    > > - if (sg[nsegs - 1].length + nbytes > q->max_segment_size)
    > > + if (sg->length + nbytes > q->max_segment_size)
    > > goto new_segment;
    > >
    > > if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
    > > @@ -1336,14 +1340,15 @@ int blk_rq_map_sg(request_queue_t *q, struct request *rq, struct scatterlist *sg
    > > if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
    > > goto new_segment;
    > >
    > > - sg[nsegs - 1].length += nbytes;
    > > + sg->length += nbytes;
    > > } else {
    > > new_segment:
    > > - memset(&sg[nsegs],0,sizeof(struct scatterlist));
    >
    > Is this intended? If so why this is no longer needed?

    It is, actually it's even required. All fields input fields should be
    set, the mapping/iommu helpers should set all output fields.

    But I understand your concerns, it's definitely something that should be
    kept an eye on. And I have so far. I even listed it as the primary
    concern in an email (off list) to Tomo today.

    --
    Jens Axboe

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