[PATCH v1 1/4] block: bio: introduce helpers to get the 1st and last bvec

[PATCH v1 1/4] block: bio: introduce helpers to get the 1st and last bvec

[Ming Lei]

The bio passed to bio_will_gap() may be fast cloned from upper
layer(dm, md, bcache, fs, ...), or from bio splitting in block
core.

Unfortunately bio_will_gap() just figures out the last bvec via
'bi_io_vec[prev->bi_vcnt - 1]' directly, and this way is obviously
wrong.

This patch introduces two helpers for getting the first and last
bvec of one bio for fixing the issue.

Cc: stable@vger.kernel.org
Reported-by: Sagi Grimberg <sagig@dev.mellanox.co.il>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
 include/linux/bio.h | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 5349e68..3ce2e45 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -310,6 +310,47 @@ static inline void bio_clear_flag(struct bio *bio, unsigned int bit)
 	bio->bi_flags &= ~(1U << bit);
 }
 
+static inline void bio_get_first_bvec(struct bio *bio, struct bio_vec *bv)
+{
+	*bv = bio_iovec(bio);
+}
+
+/*
+ * bio_get_last_bvec() is introduced to get the last bvec of one
+ * bio for bio_will_gap().
+ */
+static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
+{
+	struct bvec_iter iter = bio->bi_iter;
+	int idx;
+
+	if (!bio_flagged(bio, BIO_CLONED)) {
+		*bv = bio->bi_io_vec[bio->bi_vcnt - 1];
+		return;
+	}
+
+	if (unlikely(!bio_multiple_segments(bio))) {
+		*bv = bio_iovec(bio);
+		return;
+	}
+
+	bio_advance_iter(bio, &iter, iter.bi_size);
+
+	if (!iter.bi_bvec_done)
+		idx = iter.bi_idx - 1;
+	else	/* in the middle of bvec */
+		idx = iter.bi_idx;
+
+	*bv = bio->bi_io_vec[idx];
+
+	/*
+	 * iter.bi_bvec_done records actual length of the last bvec
+	 * if this bio ends in the middle of one io vector
+	 */
+	if (iter.bi_bvec_done)
+		bv->bv_len = iter.bi_bvec_done;
+}
+
 enum bip_flags {
 	BIP_BLOCK_INTEGRITY	= 1 << 0, /* block layer owns integrity data */
 	BIP_MAPPED_INTEGRITY	= 1 << 1, /* ref tag has been remapped */
-- 
1.9.1

[PATCH v1 3/4] block: get the 1st and last bvec via helpers

[Ming Lei]

This patch applies the two introduced helpers to
figure out the 1st and last bvec, and fixes the
original way after bio splitting.

Cc: stable@vger.kernel.org
Reported-by: Sagi Grimberg <sagig@dev.mellanox.co.il>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
 include/linux/blkdev.h | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 5023401..de4fc002 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1394,11 +1394,16 @@ static inline bool bvec_gap_to_prev(struct request_queue *q,
 static inline bool bio_will_gap(struct request_queue *q, struct bio *prev,
 			 struct bio *next)
 {
-	if (!bio_has_data(prev) || !queue_virt_boundary(q))
+	if (!bio_has_data(prev) || !queue_virt_boundary(q)) {
 		return false;
+	} else {
+		struct bio_vec pb, nb;
 
-	return bvec_gap_to_prev(q, &prev->bi_io_vec[prev->bi_vcnt - 1],
-				next->bi_io_vec[0].bv_offset);
+		bio_get_last_bvec(prev, &pb);
+		bio_get_first_bvec(next, &nb);
+
+		return __bvec_gap_to_prev(q, &pb, nb.bv_offset);
+	}
 }
 
 static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
-- 
1.9.1

Re: [PATCH v1 1/4] block: bio: introduce helpers to get the 1st and last bvec

[Sagi Grimberg]

Looks fine,

Reviewed-by: Sagi Grimberg <sagig@mellanox.com>

Re: [PATCH v1 3/4] block: get the 1st and last bvec via helpers

[Sagi Grimberg]

Looks fine,

Reviewed-by: Sagi Grimberg <sagig@mellanox.com>

Re: [PATCH v1 1/4] block: bio: introduce helpers to get the 1st and last bvec

[Christoph Hellwig]

> +/*
> + * bio_get_last_bvec() is introduced to get the last bvec of one
> + * bio for bio_will_gap().
> + */

I don't think this comment adds any value.

Otherwise looks fine:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v1 3/4] block: get the 1st and last bvec via helpers

[Christoph Hellwig]

On Fri, Feb 19, 2016 at 11:20:21AM +0800, Ming Lei wrote:
> This patch applies the two introduced helpers to
> figure out the 1st and last bvec, and fixes the
> original way after bio splitting.

Looks fine,

Reviewed-by: Christoph Hellwig <hch@lst.de>