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SubjectRe: [PATCH 5/7] block: Find bio sector offset given idx and offset
On Wed, Oct 01 2008, Martin K. Petersen wrote:
> Helper function to find the sector offset in a bio given bvec index
> and page offset.
>
> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
> ---
> fs/bio.c | 34 ++++++++++++++++++++++++++++++++++
> include/linux/bio.h | 1 +
> 2 files changed, 35 insertions(+), 0 deletions(-)
>
> diff --git a/fs/bio.c b/fs/bio.c
> index e56e768..55ee2fd 100644
> --- a/fs/bio.c
> +++ b/fs/bio.c
> @@ -1300,6 +1300,40 @@ struct bio_pair *bio_split(struct bio *bi, mempool_t *pool, int first_sectors)
> return bp;
> }
>
> +/**
> + * bio_sector_offset - Find hardware sector offset in bio
> + * @bio: bio to inspect
> + * @index: bio_vec index
> + * @offset: offset in bv_page
> + *
> + * Return the number of hardware sectors between beginning of bio
> + * and an end point indicated by a bio_vec index and an offset
> + * within that vector's page.
> + */
> +sector_t bio_sector_offset(struct bio *bio, unsigned short index,
> + unsigned int offset)
> +{
> + struct bio_vec *bv;
> + unsigned int sector_sz = bio->bi_bdev->bd_disk->queue->hardsect_size;
> + sector_t sectors;
> + int i;
> +
> + sectors = 0;
> +
> + BUG_ON(index >= bio->bi_vcnt);
> +
> + bio_for_each_segment(bv, bio, i) {
> + if (i == index) {
> + if (offset > bv->bv_offset)
> + sectors += (offset - bv->bv_offset) / sector_sz;
> + return sectors;
> + }
> +
> + sectors += bv->bv_len / sector_sz;
> + }
> +
> + BUG();
> +}

Too may BUG's there, me thinks, and the interface looks fragile. What if
the bio is alreday done (bi_idx == bi_vcnt)? I'd prefer something ala:

sector_t bio_sector_offset(struct bio *bio, unsigned short index,
unsigned int offset)
{
unsigned int sector_sz = queue_hardsect_size(bio->bi_bdev->bd_disk->queue);
struct bio_vec *bv;
sector_t sectors;
int i;

sectors = 0;

/* total start of bio current start? */
#if 0
if (index >= bio->bi_vcnt)
index = bio->bi_vcnt - 1;

__bio_for_each_segment(bv, bio, i, 0) {
#else
if (index > bio->bi_idx)
return 0;

bio_for_each_segment(bv, bio, i) {
#endif
if (i == index) {
if (offset > bv->bv_offset)
sectors += (offset - bv->bv_offset) / sector_sz;
break;
}

sectors += bv->bv_len / sector_sz;
}

return sectors;
}

Depending on which interface you want, pick one of the if/else parts :-)

--
Jens Axboe



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