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

Commit Message

Ming Lei Feb. 19, 2016, 3:20 a.m. UTC

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: [e-mail]
Reported-by: Sagi Grimberg <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Signed-off-by: Ming Lei <[e-mail]>
---
 include/linux/bio.h | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

Comments

Sagi Grimberg Feb. 21, 2016, 9:38 a.m. UTC | #1

Looks fine,

Reviewed-by: Sagi Grimberg <[e-mail]>
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Christoph Hellwig Feb. 22, 2016, 8:59 a.m. UTC | #2

> +/*
> + * 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 <[e-mail]>
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Patch

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 */