Merge tag 'libnvdimm-for-5.1' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm...

[sfrench/cifs-2.6.git] / Documentation / block / biovecs.txt

diff --git a/Documentation/block/biovecs.txt b/Documentation/block/biovecs.txt
index 25689584e6e045b44202e314ca4a803a4a3cca56..ce6eccaf5df7aa6939410dabcb52bf367c6fa59b 100644 (file)
--- 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()