[PATCH V9 16/19] block: document usage of bio iterator helpers
From: Ming Lei <hidden>
Date: 2018-11-13 15:16:49
Also in:
lkml
Subsystem:
block layer, documentation, the rest · Maintainers:
Jens Axboe, Jonathan Corbet, Linus Torvalds
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. Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Ming Lei <redacted> --- Documentation/block/biovecs.txt | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+)
diff --git a/Documentation/block/biovecs.txt b/Documentation/block/biovecs.txt
index 25689584e6e0..bfafb70d0d9e 100644
--- a/Documentation/block/biovecs.txt
+++ b/Documentation/block/biovecs.txt@@ -117,3 +117,29 @@ 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, and usually they are used by filesystem code, and driver +shouldn't use them because bio may have been split before they got to 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 bvec, and the local +variable of 'struct bio_vec' or the reference records single-page IO +vector during the itearation: + + bio_for_each_segment() + bio_for_each_segment_all() + +* The following helper iterates over multi-page bvec, and each bvec may +include multiple physically contiguous pages, and the local variable of +'struct bio_vec' or the reference records multi-page IO vector during the +itearation: + + bio_for_each_bvec()
--
2.9.5