[PATCH 2/4] block: factor out a bio_await helper

[Christoph Hellwig <hch@lst.de>]

Add a new helper to wait for a bio and anything chained off it to
complete synchronous after kicking 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 did, having the flag set makes more sense.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 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..c7e75d532666 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
+ * @kick:	function called to "kick off" the bio
+ * @priv:	private data passed to @kick.
  *
- * 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 @kick.  The wait for the bio is set up before calling
+ * @kick to ensure that the completion is captured.  If @kick 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 (*kick)(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 (kick)
+		kick(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..adcca9ad4eec 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 (*kick)(struct bio *bio, void *priv));
 
 int __must_check bio_add_page(struct bio *bio, struct page *page, unsigned len,
 			      unsigned off);
-- 
2.47.3