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block: improve the submit_bio and generic_make_request documentation

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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>
This commit is contained in:
Christoph Hellwig 2020-04-28 13:27:53 +02:00 committed by Jens Axboe
parent e1b586f2b8
commit 3fdd40861d
1 changed files with 12 additions and 23 deletions
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35
block/blk-core.c
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@ -992,28 +992,13 @@ 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)
{
@ -1152,10 +1137,14 @@ 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)
{