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:

quoted

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.

quoted

Signed-off-by: Kent Overstreet <redacted>
CC: Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>
---
 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.

quoted

--- 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