[PATCH 1/3] block: add a bio_reuse helper

[Christoph Hellwig <hch@lst.de>]

Add a helper to allow an existing bio to be resubmitted withtout
having to re-add the payload.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
---
 block/bio.c         | 29 +++++++++++++++++++++++++++++
 include/linux/bio.h |  1 +
 2 files changed, 30 insertions(+)

diff --git a/block/bio.c b/block/bio.c
index e726c0e280a8..ed99368c662f 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -311,6 +311,35 @@ void bio_reset(struct bio *bio, struct block_device *bdev, blk_opf_t opf)
 }
 EXPORT_SYMBOL(bio_reset);
 
+/**
+ * bio_reuse - reuse a bio with the payload left intact
+ * @bio bio to reuse
+ *
+ * Allow reusing an existing bio for another operation with all set up
+ * fields including the payload, device and end_io handler left intact.
+ *
+ * Typically used for bios first used to read data which is then written
+ * to another location without modification.  This must be used by the
+ * I/O submitter on an bio that is not in flight.  Can't be used for
+ * cloned bios.
+ */
+void bio_reuse(struct bio *bio)
+{
+	unsigned short vcnt = bio->bi_vcnt, i;
+	bio_end_io_t *end_io = bio->bi_end_io;
+	void *private = bio->bi_private;
+
+	WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED));
+
+	bio_reset(bio, bio->bi_bdev, bio->bi_opf);
+	for (i = 0; i < vcnt; i++)
+		bio->bi_iter.bi_size += bio->bi_io_vec[i].bv_len;
+	bio->bi_vcnt = vcnt;
+	bio->bi_private = private;
+	bio->bi_end_io = end_io;
+}
+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 ad2d57908c1c..c0190f8badde 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -414,6 +414,7 @@ static inline void bio_init_inline(struct bio *bio, struct block_device *bdev,
 }
 extern void bio_uninit(struct bio *);
 void bio_reset(struct bio *bio, struct block_device *bdev, blk_opf_t opf);
+void bio_reuse(struct bio *bio);
 void bio_chain(struct bio *, struct bio *);
 
 int __must_check bio_add_page(struct bio *bio, struct page *page, unsigned len,
-- 
2.47.3