X-Git-Url: http://mj.ucw.cz/gitweb/?a=blobdiff_plain;f=lib%2Fasio.h;h=6773c81fd1333d95a610381b509f9dd2ed7922ef;hb=c4bf633211b0424492b5a3937d6a6d2e0d79a4cf;hp=45c7fb9f40d1899040814e9b8e9b08f7513833bf;hpb=7e1f93ce44a60eb194562680cbd662866eee829a;p=libucw.git

diff --git a/lib/asio.h b/lib/asio.h
index 45c7fb9f..6773c81f 100644
--- a/lib/asio.h
+++ b/lib/asio.h
@@ -13,7 +13,19 @@
 #include "lib/workqueue.h"
 #include "lib/clists.h"
 
-/* FIXME: Comment, especially on request ordering */
+/*
+ *  This module takes care of scheduling and executing asynchronous I/O requests
+ *  on files opened with O_DIRECT. It is primarily used by the fb-direct fastbuf
+ *  back-end, but you can use it explicitly, too.
+ *
+ *  You can define several I/O queues, each for use by a single thread. Requests
+ *  on a single queue are always processed in order of their submits, requests
+ *  from different queues may be interleaved (although the current implementation
+ *  does not do so). Normal read and write requests are returned to their queue
+ *  when they are completed. Write-back requests are automatically freed when
+ *  done, but the number of such requests in fly is limited in order to avoid
+ *  consuming all memory, so a submit of a write-back request can block.
+ */
 
 struct asio_queue {
   uns buffer_size;			// How large buffers do we use [user-settable]
@@ -24,6 +36,7 @@ struct asio_queue {
   clist idle_list;			// Recycled requests waiting for get
   clist done_list;			// Finished requests
   struct work_queue queue;
+  uns use_count;			// For use by the caller
 };
 
 enum asio_op {
@@ -43,6 +56,7 @@ struct asio_request {
   int status;
   int returned_errno;
   int submitted;
+  void *user_data;			// For use by the caller
 };
 
 void asio_init_queue(struct asio_queue *q);			// Initialize a new queue