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authorNeilBrown <neilb@suse.de>2007-09-25 12:35:59 +0200
committerJens Axboe <axboe@carl.home.kernel.dk>2007-10-10 09:25:56 +0200
commit5705f7021748a69d84d6567e68e8851dab551464 (patch)
tree5a6dbc8fc6055c0334f4a97540e36a7844b9c482 /Documentation/block/biodoc.txt
parent9dfa52831e96194b8649613e3131baa2c109f7dc (diff)
Introduce rq_for_each_segment replacing rq_for_each_bio
Every usage of rq_for_each_bio wraps a usage of bio_for_each_segment, so these can be combined into rq_for_each_segment. We define "struct req_iterator" to hold the 'bio' and 'index' that are needed for the double iteration. Signed-off-by: Neil Brown <neilb@suse.de> Various compile fixes by me... Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'Documentation/block/biodoc.txt')
-rw-r--r--Documentation/block/biodoc.txt20
1 files changed, 10 insertions, 10 deletions
diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt
index 8af392fc6ef..dc3f49e3e53 100644
--- a/Documentation/block/biodoc.txt
+++ b/Documentation/block/biodoc.txt
@@ -477,9 +477,9 @@ With this multipage bio design:
the same bi_io_vec array, but with the index and size accordingly modified)
- A linked list of bios is used as before for unrelated merges (*) - this
avoids reallocs and makes independent completions easier to handle.
-- Code that traverses the req list needs to make a distinction between
- segments of a request (bio_for_each_segment) and the distinct completion
- units/bios (rq_for_each_bio).
+- Code that traverses the req list can find all the segments of a bio
+ by using rq_for_each_segment. This handles the fact that a request
+ has multiple bios, each of which can have multiple segments.
- Drivers which can't process a large bio in one shot can use the bi_idx
field to keep track of the next bio_vec entry to process.
(e.g a 1MB bio_vec needs to be handled in max 128kB chunks for IDE)
@@ -664,14 +664,14 @@ in lvm or md.
3.2.1 Traversing segments and completion units in a request
-The macros bio_for_each_segment() and rq_for_each_bio() should be used for
-traversing the bios in the request list (drivers should avoid directly
-trying to do it themselves). Using these helpers should also make it easier
-to cope with block changes in the future.
+The macro rq_for_each_segment() should be used for traversing the bios
+in the request list (drivers should avoid directly trying to do it
+themselves). Using these helpers should also make it easier to cope
+with block changes in the future.
- rq_for_each_bio(bio, rq)
- bio_for_each_segment(bio_vec, bio, i)
- /* bio_vec is now current segment */
+ struct req_iterator iter;
+ rq_for_each_segment(bio_vec, rq, iter)
+ /* bio_vec is now current segment */
I/O completion callbacks are per-bio rather than per-segment, so drivers
that traverse bio chains on completion need to keep that in mind. Drivers