[PATCH 3/5] block: factor out a bio_await helper

Christoph Hellwig
2026-04-07T14:05:57Z

Add a new helper to wait for a bio and anything chained off it to
complete synchronously after submitting it. This factors common code out
of submit_bio_wait and bio_await_chain and will also be useful for
file system code and thus is exported.

Note that this will now set REQ_SYNC also for the bio_await case for
consistency. Nothing should look at the flag in the end_io handler,
but if something does having the flag set makes more sense.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
---
block/bio.c | 53 +++++++++++++++++++++++++++++++--------------
include/linux/bio.h | 2 ++
2 files changed, 39 insertions(+), 16 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 434e41182c05..61d65c544bcc 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1468,17 +1468,20 @@ static void bio_wait_end_io(struct bio *bio)
}

/**
- * submit_bio_wait - submit a bio, and wait until it completes
- * @bio: The &struct bio which describes the I/O
+ * bio_await - call a function on a bio, and wait until it completes
+ * @bio: the bio which describes the I/O
+ * @submit: function called to submit the bio
+ * @priv: private data passed to @submit
*
- * Simple wrapper around submit_bio(). Returns 0 on success, or the error from
- * bio_endio() on failure.
+ * Wait for the bio as well as any bio chained off it after executing the
+ * passed in callback @submit. The wait for the bio is set up before calling
+ * @submit to ensure that the completion is captured. If @submit is %NULL,
+ * submit_bio() is used instead to submit the bio.
*
- * WARNING: Unlike to how submit_bio() is usually used, this function does not
- * result in bio reference to be consumed. The caller must drop the reference
- * on his own.
+ * Note: this overrides the bi_private and bi_end_io fields in the bio.
*/
-int submit_bio_wait(struct bio *bio)
+void bio_await(struct bio *bio, void *priv,
+ void (*submit)(struct bio *bio, void *priv))
{
DECLARE_COMPLETION_ONSTACK_MAP(done,
bio->bi_bdev->bd_disk->lockdep_map);
@@ -1486,13 +1489,37 @@ int submit_bio_wait(struct bio *bio)
bio->bi_private = &done;
bio->bi_end_io = bio_wait_end_io;
bio->bi_opf |= REQ_SYNC;
- submit_bio(bio);
+ if (submit)
+ submit(bio, priv);
+ else
+ submit_bio(bio);
blk_wait_io(&done);
+}
+EXPORT_SYMBOL_GPL(bio_await);

+/**
+ * submit_bio_wait - submit a bio, and wait until it completes
+ * @bio: The &struct bio which describes the I/O
+ *
+ * Simple wrapper around submit_bio(). Returns 0 on success, or the error from
+ * bio_endio() on failure.
+ *
+ * WARNING: Unlike to how submit_bio() is usually used, this function does not
+ * result in bio reference to be consumed. The caller must drop the reference
+ * on his own.
+ */
+int submit_bio_wait(struct bio *bio)
+{
+ bio_await(bio, NULL, NULL);
return blk_status_to_errno(bio->bi_status);
}
EXPORT_SYMBOL(submit_bio_wait);

+static void bio_endio_cb(struct bio *bio, void *priv)
+{
+ bio_endio(bio);
+}
+
/**
* bdev_rw_virt - synchronously read into / write from kernel mapping
* @bdev: block device to access
@@ -1528,13 +1555,7 @@ EXPORT_SYMBOL_GPL(bdev_rw_virt);
*/
void bio_await_chain(struct bio *bio)
{
- DECLARE_COMPLETION_ONSTACK_MAP(done,
- bio->bi_bdev->bd_disk->lockdep_map);
-
- bio->bi_private = &done;
- bio->bi_end_io = bio_wait_end_io;
- bio_endio(bio);
- blk_wait_io(&done);
+ bio_await(bio, NULL, bio_endio_cb);
bio_put(bio);
}

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 984844d2870b..97d747320b35 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -432,6 +432,8 @@ 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 *);
+void bio_await(struct bio *bio, void *priv,
+ void (*submit)(struct bio *bio, void *priv));

int __must_check bio_add_page(struct bio *bio, struct page *page, unsigned len,
unsigned off);
--
2.47.3