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Introduce rq_for_each_segment replacing rq_for_each_bio

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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 <[email protected]>

Various compile fixes by me...

Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
NeilBrown 2007-09-25 12:35:59 +02:00 • committed by Jens Axboe
commit 5705f70217
14 changed files with 131 additions and 162 deletions
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20
Documentation/block/biodoc.txt
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@ -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