[PATCH 1/4] block: introduce bio_clone_bioset_partial()

Ming Lei
2017-02-05T06:22:37Z

md still need bio clone(not the fast version) for behind write,
and it is more efficient to use bio_clone_bioset_partial().

The idea is simple and just copy the bvecs range specified from
parameters.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
block/bio.c | 61 +++++++++++++++++++++++++++++++++++++++++------------
include/linux/bio.h | 11 ++++++++--
2 files changed, 57 insertions(+), 15 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 4b564d0c3e29..5eec5e08417f 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -625,21 +625,20 @@ struct bio *bio_clone_fast(struct bio *bio, gfp_t gfp_mask, struct bio_set *bs)
}
EXPORT_SYMBOL(bio_clone_fast);

-/**
- * bio_clone_bioset - clone a bio
- * @bio_src: bio to clone
- * @gfp_mask: allocation priority
- * @bs: bio_set to allocate from
- *
- * Clone bio. Caller will own the returned bio, but not the actual data it
- * points to. Reference count of returned bio will be one.
- */
-struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
- struct bio_set *bs)
+static struct bio *__bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
+ struct bio_set *bs, int offset,
+ int size)
{
struct bvec_iter iter;
struct bio_vec bv;
struct bio *bio;
+ struct bvec_iter iter_src = bio_src->bi_iter;
+
+ /* for supporting partial clone */
+ if (offset || size != bio_src->bi_iter.bi_size) {
+ bio_advance_iter(bio_src, &iter_src, offset);
+ iter_src.bi_size = size;
+ }

/*
* Pre immutable biovecs, __bio_clone() used to just do a memcpy from
@@ -663,7 +662,8 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
* __bio_clone_fast() anyways.
*/

- bio = bio_alloc_bioset(gfp_mask, bio_segments(bio_src), bs);
+ bio = bio_alloc_bioset(gfp_mask, __bio_segments(bio_src,
+ &iter_src), bs);
if (!bio)
return NULL;
bio->bi_bdev = bio_src->bi_bdev;
@@ -680,7 +680,7 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
bio->bi_io_vec[bio->bi_vcnt++] = bio_src->bi_io_vec[0];
break;
default:
- bio_for_each_segment(bv, bio_src, iter)
+ __bio_for_each_segment(bv, bio_src, iter, iter_src)
bio->bi_io_vec[bio->bi_vcnt++] = bv;
break;
}
@@ -699,9 +699,44 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,

return bio;
}
+
+/**
+ * bio_clone_bioset - clone a bio
+ * @bio_src: bio to clone
+ * @gfp_mask: allocation priority
+ * @bs: bio_set to allocate from
+ *
+ * Clone bio. Caller will own the returned bio, but not the actual data it
+ * points to. Reference count of returned bio will be one.
+ */
+struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
+ struct bio_set *bs)
+{
+ return __bio_clone_bioset(bio_src, gfp_mask, bs, 0,
+ bio_src->bi_iter.bi_size);
+}
EXPORT_SYMBOL(bio_clone_bioset);

/**
+ * bio_clone_bioset_partial - clone a partial bio
+ * @bio_src: bio to clone
+ * @gfp_mask: allocation priority
+ * @bs: bio_set to allocate from
+ * @offset: cloned starting from the offset
+ * @size: size for the cloned bio
+ *
+ * Clone bio. Caller will own the returned bio, but not the actual data it
+ * points to. Reference count of returned bio will be one.
+ */
+struct bio *bio_clone_bioset_partial(struct bio *bio_src, gfp_t gfp_mask,
+ struct bio_set *bs, int offset,
+ int size)
+{
+ return __bio_clone_bioset(bio_src, gfp_mask, bs, offset, size);
+}
+EXPORT_SYMBOL(bio_clone_bioset_partial);
+
+/**
* bio_add_pc_page - attempt to add page to bio
* @q: the target queue
* @bio: destination bio
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 7cf8a6c70a3f..8e521194f6fc 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -183,7 +183,7 @@ static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter,

#define bio_iter_last(bvec, iter) ((iter).bi_size == (bvec).bv_len)

-static inline unsigned bio_segments(struct bio *bio)
+static inline unsigned __bio_segments(struct bio *bio, struct bvec_iter *bvec)
{
unsigned segs = 0;
struct bio_vec bv;
@@ -205,12 +205,17 @@ static inline unsigned bio_segments(struct bio *bio)
break;
}

- bio_for_each_segment(bv, bio, iter)
+ __bio_for_each_segment(bv, bio, iter, *bvec)
segs++;

return segs;
}

+static inline unsigned bio_segments(struct bio *bio)
+{
+ return __bio_segments(bio, &bio->bi_iter);
+}
+
/*
* get a reference to a bio, so it won't disappear. the intended use is
* something like:
@@ -384,6 +389,8 @@ extern void bio_put(struct bio *);
extern void __bio_clone_fast(struct bio *, struct bio *);
extern struct bio *bio_clone_fast(struct bio *, gfp_t, struct bio_set *);
extern struct bio *bio_clone_bioset(struct bio *, gfp_t, struct bio_set *bs);
+extern struct bio *bio_clone_bioset_partial(struct bio *, gfp_t,
+ struct bio_set *, int, int);

extern struct bio_set *fs_bio_set;

--
2.7.4