diff options
| author | NeilBrown <neilb@suse.de> | 2007-09-25 06:35:59 -0400 |
|---|---|---|
| committer | Jens Axboe <axboe@carl.home.kernel.dk> | 2007-10-10 03:25:56 -0400 |
| commit | 5705f7021748a69d84d6567e68e8851dab551464 (patch) | |
| tree | 5a6dbc8fc6055c0334f4a97540e36a7844b9c482 /Documentation/block/biodoc.txt | |
| parent | 9dfa52831e96194b8649613e3131baa2c109f7dc (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.txt | 20 |
1 files changed, 10 insertions, 10 deletions
diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt index 8af392fc6ef0..dc3f49e3e539 100644 --- a/Documentation/block/biodoc.txt +++ b/Documentation/block/biodoc.txt | |||
| @@ -477,9 +477,9 @@ With this multipage bio design: | |||
| 477 | the same bi_io_vec array, but with the index and size accordingly modified) | 477 | the same bi_io_vec array, but with the index and size accordingly modified) |
| 478 | - A linked list of bios is used as before for unrelated merges (*) - this | 478 | - A linked list of bios is used as before for unrelated merges (*) - this |
| 479 | avoids reallocs and makes independent completions easier to handle. | 479 | avoids reallocs and makes independent completions easier to handle. |
| 480 | - Code that traverses the req list needs to make a distinction between | 480 | - Code that traverses the req list can find all the segments of a bio |
| 481 | segments of a request (bio_for_each_segment) and the distinct completion | 481 | by using rq_for_each_segment. This handles the fact that a request |
| 482 | units/bios (rq_for_each_bio). | 482 | has multiple bios, each of which can have multiple segments. |
| 483 | - Drivers which can't process a large bio in one shot can use the bi_idx | 483 | - Drivers which can't process a large bio in one shot can use the bi_idx |
| 484 | field to keep track of the next bio_vec entry to process. | 484 | field to keep track of the next bio_vec entry to process. |
| 485 | (e.g a 1MB bio_vec needs to be handled in max 128kB chunks for IDE) | 485 | (e.g a 1MB bio_vec needs to be handled in max 128kB chunks for IDE) |
| @@ -664,14 +664,14 @@ in lvm or md. | |||
| 664 | 664 | ||
| 665 | 3.2.1 Traversing segments and completion units in a request | 665 | 3.2.1 Traversing segments and completion units in a request |
| 666 | 666 | ||
| 667 | The macros bio_for_each_segment() and rq_for_each_bio() should be used for | 667 | The macro rq_for_each_segment() should be used for traversing the bios |
| 668 | traversing the bios in the request list (drivers should avoid directly | 668 | in the request list (drivers should avoid directly trying to do it |
| 669 | trying to do it themselves). Using these helpers should also make it easier | 669 | themselves). Using these helpers should also make it easier to cope |
| 670 | to cope with block changes in the future. | 670 | with block changes in the future. |
| 671 | 671 | ||
| 672 | rq_for_each_bio(bio, rq) | 672 | struct req_iterator iter; |
| 673 | bio_for_each_segment(bio_vec, bio, i) | 673 | rq_for_each_segment(bio_vec, rq, iter) |
| 674 | /* bio_vec is now current segment */ | 674 | /* bio_vec is now current segment */ |
| 675 | 675 | ||
| 676 | I/O completion callbacks are per-bio rather than per-segment, so drivers | 676 | I/O completion callbacks are per-bio rather than per-segment, so drivers |
| 677 | that traverse bio chains on completion need to keep that in mind. Drivers | 677 | that traverse bio chains on completion need to keep that in mind. Drivers |