X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=Documentation%2Fblock%2Fbiodoc.txt;h=dc3f49e3e5392891f10d700567363b3446358b67;hb=b981d8b3f5e008ff10d993be633ad00564fc22cd;hp=c6c9a9c10d7f88b5f894990e45878acadbb2ea64;hpb=cfee47f99bc14a6d7c6b0be2284db2cef310a815;p=linux-2.6

diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt
index c6c9a9c10d..dc3f49e3e5 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
@@ -740,12 +740,12 @@ Block now offers some simple generic functionality to help support command
 queueing (typically known as tagged command queueing), ie manage more than
 one outstanding command on a queue at any given time.
 
-	blk_queue_init_tags(request_queue_t *q, int depth)
+	blk_queue_init_tags(struct request_queue *q, int depth)
 
 	Initialize internal command tagging structures for a maximum
 	depth of 'depth'.
 
-	blk_queue_free_tags((request_queue_t *q)
+	blk_queue_free_tags((struct request_queue *q)
 
 	Teardown tag info associated with the queue. This will be done
 	automatically by block if blk_queue_cleanup() is called on a queue
@@ -754,7 +754,7 @@ one outstanding command on a queue at any given time.
 The above are initialization and exit management, the main helpers during
 normal operations are:
 
-	blk_queue_start_tag(request_queue_t *q, struct request *rq)
+	blk_queue_start_tag(struct request_queue *q, struct request *rq)
 
 	Start tagged operation for this request. A free tag number between
 	0 and 'depth' is assigned to the request (rq->tag holds this number),
@@ -762,7 +762,7 @@ normal operations are:
 	for this queue is already achieved (or if the tag wasn't started for
 	some other reason), 1 is returned. Otherwise 0 is returned.
 
-	blk_queue_end_tag(request_queue_t *q, struct request *rq)
+	blk_queue_end_tag(struct request_queue *q, struct request *rq)
 
 	End tagged operation on this request. 'rq' is removed from the internal
 	book keeping structures.
@@ -781,7 +781,7 @@ queue. For instance, on IDE any tagged request error needs to clear both
 the hardware and software block queue and enable the driver to sanely restart
 all the outstanding requests. There's a third helper to do that:
 
-	blk_queue_invalidate_tags(request_queue_t *q)
+	blk_queue_invalidate_tags(struct request_queue *q)
 
 	Clear the internal block tag queue and re-add all the pending requests
 	to the request queue. The driver will receive them again on the
@@ -946,6 +946,13 @@ elevator_merged_fn		called when a request in the scheduler has been
 				scheduler for example, to reposition the request
 				if its sorting order has changed.
 
+elevator_allow_merge_fn		called whenever the block layer determines
+				that a bio can be merged into an existing
+				request safely. The io scheduler may still
+				want to stop a merge at this point if it
+				results in some sort of conflict internally,
+				this hook allows it to do that.
+
 elevator_dispatch_fn		fills the dispatch queue with ready requests.
 				I/O schedulers are free to postpone requests by
 				not filling the dispatch queue unless @force