[PATCH] block: document io scheduler allow_merge_fn hook

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt
index c6c9a9c10d7f..3adaace328a6 100644
--- a/Documentation/block/biodoc.txt
+++ b/Documentation/block/biodoc.txt
@@ -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