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| author |   Ming Lei <ming.lei@redhat.com> | 2019-02-15 19:13:22 +0800 |
|---|---|---|
| committer |   Jens Axboe <axboe@kernel.dk> | 2019-02-15 08:40:12 -0700 |
| commit | ac4fa1d107addb2c6b21067d8945a39316a09fc8 (patch) | |
| tree | a7a7763070c6b45f31fab2209874b84b4a4630ff /Documentation/block | |
| parent | block: always define BIO_MAX_PAGES as 256 (diff) | |
| download | linux-dev-ac4fa1d107addb2c6b21067d8945a39316a09fc8.tar.xz linux-dev-ac4fa1d107addb2c6b21067d8945a39316a09fc8.zip | |
block: document usage of bio iterator helpers
Now multi-page bvec is supported, some helpers may return page by
page, meantime some may return segment by segment, this patch
documents the usage.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'Documentation/block')
| -rw-r--r-- | Documentation/block/biovecs.txt | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/Documentation/block/biovecs.txt b/Documentation/block/biovecs.txt index 25689584e6e0..ce6eccaf5df7 100644 --- a/Documentation/block/biovecs.txt +++ b/Documentation/block/biovecs.txt @@ -117,3 +117,28 @@ Other implications: size limitations and the limitations of the underlying devices. Thus there's no need to define ->merge_bvec_fn() callbacks for individual block drivers. + +Usage of helpers: +================= + +* The following helpers whose names have the suffix of "_all" can only be used +on non-BIO_CLONED bio. They are usually used by filesystem code. Drivers +shouldn't use them because the bio may have been split before it reached the +driver. + + bio_for_each_segment_all() + bio_first_bvec_all() + bio_first_page_all() + bio_last_bvec_all() + +* The following helpers iterate over single-page segment. The passed 'struct +bio_vec' will contain a single-page IO vector during the iteration + + bio_for_each_segment() + bio_for_each_segment_all() + +* The following helpers iterate over multi-page bvec. The passed 'struct +bio_vec' will contain a multi-page IO vector during the iteration + + bio_for_each_bvec() + rq_for_each_bvec() |