[PATCH] (Documentation) append more detail explanation to the I/O scheduler API.

[Hiroyasu OHYAMA <ohyama_sec@ariel-networks.com>]

 This patch append more detail explanation to the Documentation of API of I/O scheduler.

 Thank you for reading.

---
diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt
index 8d2158a..7c04f54 100644
--- a/Documentation/block/biodoc.txt
+++ b/Documentation/block/biodoc.txt
@@ -935,7 +935,12 @@ keeping work.
 4.1. I/O scheduler API

  The functions an elevator may implement are: (* are mandatory)
-elevator_merge_fn    called to query requests for merge with a bio
+elevator_merge_fn    called to query requests for merge with a bio. This method
+       have two following works. One is to indicate how to merge request
+       with bio from head or tail. This function doesn't merge them actually,
+       but just indicate direction for merging from head or tail, or that
+       there is no request with that bio can merge. Another work is to get
+       the request object which is merged, if the bio can do.

 elevator_merge_req_fn    called when two requests get merged. the one
         which gets merged into the other one will be