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

Ming Lei
2016-02-19T03:20:40Z

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