block: add a bio_reuse helper

Add a helper to allow an existing bio to be resubmitted without
having to re-add the payload.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jens Axboe <[email protected]>
Reviewed-by: Hans Holmberg <[email protected]>
Reviewed-by: Carlos Maiolino <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Reviewed-by: "Darrick J. Wong" <[email protected]>

Author: Christoph Hellwig

block/bio.c

@@ -311,6 +311,40 @@ 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
+ * @opf:	operation and flags for the next I/O
+ *
+ * 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 when @bio is first used to read data which is then written
+ * to another location without modification.  @bio must not be in-flight and
+ * owned by the caller.  Can't be used for cloned bios.
+ *
+ * Note: Can't be used when @bio has integrity or blk-crypto contexts for now.
+ * Feel free to add that support when you need it, though.
+ */
+void bio_reuse(struct bio *bio, blk_opf_t opf)
+{
+	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));
+	WARN_ON_ONCE(bio_integrity(bio));
+	WARN_ON_ONCE(bio_has_crypt_ctx(bio));
+
+	bio_reset(bio, bio->bi_bdev, 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;

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, blk_opf_t opf);
 void bio_chain(struct bio *, struct bio *);
 
 int __must_check bio_add_page(struct bio *bio, struct page *page, unsigned len,