[lkml]   [2018]   [Nov]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH V9 16/19] 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.

Cc: Christoph Hellwig <>
Signed-off-by: Ming Lei <>
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
+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
+ bio_for_each_bvec()
 \ /
  Last update: 2018-11-13 16:17    [W:0.071 / U:0.436 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site