From: Christoph Hellwig <hch@lst.de>
Date: Tue, 28 Apr 2020 13:27:53 +0200
Subject: [PATCH] block: improve the submit_bio and generic_make_request
 documentation
References: bsc#1175995,jsc#SLE-15608
Git-commit: 3fdd40861d800a4e1eb67c5158e8ab90076e2f93
Patch-mainline: v5.8-rc1

The current documentation is a little weird, as it doesn't clearly
explain which function to use, and also has the guts of the information
on generic_make_request, which is the internal interface for stacking
drivers.

Fix this up by properly documenting submit_bio, and only documenting
the differences and the use case for generic_make_request.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 block/blk-core.c | 35 ++++++++++++-----------------------
 1 file changed, 12 insertions(+), 23 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index a3d4ae1cb550..35169cd76343 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -985,28 +985,13 @@ generic_make_request_checks(struct bio *bio)
 }
 
 /**
- * generic_make_request - hand a buffer to its device driver for I/O
+ * generic_make_request - re-submit a bio to the block device layer for I/O
  * @bio:  The bio describing the location in memory and on the device.
  *
- * generic_make_request() is used to make I/O requests of block
- * devices. It is passed a &struct bio, which describes the I/O that needs
- * to be done.
- *
- * generic_make_request() does not return any status.  The
- * success/failure status of the request, along with notification of
- * completion, is delivered asynchronously through the bio->bi_end_io
- * function described (one day) else where.
- *
- * The caller of generic_make_request must make sure that bi_io_vec
- * are set to describe the memory buffer, and that bi_dev and bi_sector are
- * set to describe the device address, and the
- * bi_end_io and optionally bi_private are set to describe how
- * completion notification should be signaled.
- *
- * generic_make_request and the drivers it calls may use bi_next if this
- * bio happens to be merged with someone else, and may resubmit the bio to
- * a lower device by calling into generic_make_request recursively, which
- * means the bio should NOT be touched after the call to ->make_request_fn.
+ * This is a version of submit_bio() that shall only be used for I/O that is
+ * resubmitted to lower level drivers by stacking block drivers.  All file
+ * systems and other upper level users of the block layer should use
+ * submit_bio() instead.
  */
 blk_qc_t generic_make_request(struct bio *bio)
 {
@@ -1137,10 +1122,14 @@ EXPORT_SYMBOL_GPL(direct_make_request);
  * submit_bio - submit a bio to the block device layer for I/O
  * @bio: The &struct bio which describes the I/O
  *
- * submit_bio() is very similar in purpose to generic_make_request(), and
- * uses that function to do most of the work. Both are fairly rough
- * interfaces; @bio must be presetup and ready for I/O.
+ * submit_bio() is used to submit I/O requests to block devices.  It is passed a
+ * fully set up &struct bio that describes the I/O that needs to be done.  The
+ * bio will be send to the device described by the bi_disk and bi_partno fields.
  *
+ * The success/failure status of the request, along with notification of
+ * completion, is delivered asynchronously through the ->bi_end_io() callback
+ * in @bio.  The bio must NOT be touched by thecaller until ->bi_end_io() has
+ * been called.
  */
 blk_qc_t submit_bio(struct bio *bio)
 {
-- 
2.16.4