On Thu, Sep 20, 2012 at 04:45:44PM -0700, Tejun Heo wrote:
> On Mon, Sep 10, 2012 at 05:22:18PM -0700, Kent Overstreet wrote:
> > Prep work for immutable bio_vecs/efficient bio splitting: they require
> > auditing and removing most uses of bi_idx.
> >
> > So here we convert bio_split() to respect the current value of bi_idx
> > and use the bio_iovec() macro, instead of assuming bi_idx will be 0.
>
> I find the description a bit cryptic.
Yeah, I wasn't able to come up with a better description at the time...
how's this:
Change bio_split() to respect the current value of bi_idx
In the current code bio_split() won't be seeing partially completed bios
so this doesn't change any behaviour, but this makes the code a bit
clearer as to what bio_split() actually requires.
The immediate purpose of the patch is removing unnecessary bi_idx
references, but the end goal is to allow partial completed bios to be
submitted, which along with immutable biovecs enables effecient bio
splitting.
>
> > Signed-off-by: Kent Overstreet <koverstr...@google.com>
> > CC: Jens Axboe <ax...@kernel.dk>
> > ---
> > drivers/block/drbd/drbd_req.c | 6 +++---
> > drivers/md/raid0.c | 3 +--
> > drivers/md/raid10.c | 3 +--
> > fs/bio-integrity.c | 4 ++--
> > fs/bio.c | 7 +++----
> > 5 files changed, 10 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
> > index af69a96..57eb253 100644
> > --- a/drivers/block/drbd/drbd_req.c
> > +++ b/drivers/block/drbd/drbd_req.c
> > @@ -1155,11 +1155,11 @@ void drbd_make_request(struct request_queue *q,
> > struct bio *bio)
> >
> > /* can this bio be split generically?
> > * Maybe add our own split-arbitrary-bios function. */
> > - if (bio->bi_vcnt != 1 || bio->bi_idx != 0 || bio->bi_size >
> > DRBD_MAX_BIO_SIZE) {
> > + if (bio_segments(bio) != 1 || bio->bi_size > DRBD_MAX_BIO_SIZE) {
> > /* rather error out here than BUG in bio_split */
> > dev_err(DEV, "bio would need to, but cannot, be split: "
> > - "(vcnt=%u,idx=%u,size=%u,sector=%llu)\n",
> > - bio->bi_vcnt, bio->bi_idx, bio->bi_size,
> > + "(segments=%u,size=%u,sector=%llu)\n",
> > + bio_segments(bio), bio->bi_size,
> > (unsigned long long)bio->bi_sector);
> > bio_endio(bio, -EINVAL);
> > } else {
> > diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
> > index 387cb89..0587450 100644
> > --- a/drivers/md/raid0.c
> > +++ b/drivers/md/raid0.c
> > @@ -509,8 +509,7 @@ static void raid0_make_request(struct mddev *mddev,
> > struct bio *bio)
> > sector_t sector = bio->bi_sector;
> > struct bio_pair *bp;
> > /* Sanity check -- queue functions should prevent this
> > happening */
> > - if (bio->bi_vcnt != 1 ||
> > - bio->bi_idx != 0)
> > + if (bio_segments(bio) != 1)
> > goto bad_map;
> > /* This is a one page bio that upper layers
> > * refuse to split for us, so we need to split it.
> > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> > index 9715aaf..bbd08f5 100644
> > --- a/drivers/md/raid10.c
> > +++ b/drivers/md/raid10.c
> > @@ -1081,8 +1081,7 @@ static void make_request(struct mddev *mddev, struct
> > bio * bio)
> > || conf->prev.near_copies < conf->prev.raid_disks))) {
> > struct bio_pair *bp;
> > /* Sanity check -- queue functions should prevent this
> > happening */
> > - if (bio->bi_vcnt != 1 ||
> > - bio->bi_idx != 0)
> > + if (bio_segments(bio) != 1)
> > goto bad_map;
> > /* This is a one page bio that upper layers
> > * refuse to split for us, so we need to split it.
>
> And wonder how the description applies to the above.
>
> > --- a/fs/bio.c
> > +++ b/fs/bio.c
> > @@ -1616,8 +1616,7 @@ struct bio_pair *bio_split(struct bio *bi, int
> > first_sectors)
> > trace_block_split(bdev_get_queue(bi->bi_bdev), bi,
> > bi->bi_sector + first_sectors);
> >
> > - BUG_ON(bi->bi_vcnt != 1);
> > - BUG_ON(bi->bi_idx != 0);
> > + BUG_ON(bio_segments(bi) != 1);
> > atomic_set(&bp->cnt, 3);
> > bp->error = 0;
> > bp->bio1 = *bi;
> > @@ -1626,8 +1625,8 @@ struct bio_pair *bio_split(struct bio *bi, int
> > first_sectors)
> > bp->bio2.bi_size -= first_sectors << 9;
> > bp->bio1.bi_size = first_sectors << 9;
> >
> > - bp->bv1 = bi->bi_io_vec[0];
> > - bp->bv2 = bi->bi_io_vec[0];
> > + bp->bv1 = *bio_iovec(bi);
> > + bp->bv2 = *bio_iovec(bi);
>
> This conflicts with a recent commit from Martin. You probably wanna
> rebase.
>
> Thanks.
>
> --
> tejun
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