[PATCH 1/6] block: add a bio_reuse helper

[Christoph Hellwig <hch@lst.de>]

This abstracts out a way to reuse a bio without destroying the
bio vectors containing the data.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/bio.c         | 19 +++++++++++++++++++
 include/linux/bio.h |  1 +
 2 files changed, 20 insertions(+)

diff --git a/block/bio.c b/block/bio.c
index 70c4e1b6dd45..67393ab9abe0 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -308,6 +308,25 @@ void bio_reset(struct bio *bio)
 }
 EXPORT_SYMBOL(bio_reset);
 
+/**
+ * bio_reuse - prepare a bio for reuse
+ * @bio:	bio to reuse
+ * @size:	size of the bio 
+ *
+ * Prepares an already setup and possible used bio for reusing it another
+ * time.  Compared to bio_reset() this preserves the setup of the bio
+ * vectors containing the data.
+ */
+void bio_reuse(struct bio *bio, unsigned size)
+{
+	unsigned short vcnt = bio->bi_vcnt;
+
+	bio_reset(bio);
+	bio->bi_iter.bi_size = size;
+	bio->bi_vcnt = vcnt;
+}
+EXPORT_SYMBOL_GPL(bio_reuse);
+
 static struct bio *__bio_chain_endio(struct bio *bio)
 {
 	struct bio *parent = bio->bi_private;
diff --git a/include/linux/bio.h b/include/linux/bio.h
index f08f5fe7bd08..d114ccc4bac2 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -475,6 +475,7 @@ extern void bio_init(struct bio *bio, struct bio_vec *table,
 		     unsigned short max_vecs);
 extern void bio_uninit(struct bio *);
 extern void bio_reset(struct bio *);
+void bio_reuse(struct bio *, unsigned int);
 void bio_chain(struct bio *, struct bio *);
 
 extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
-- 
2.17.1