[PATCH] uml: add host AIO support to block driver

This adds AIO support to the ubd driver.

The driver breaks a struct request into IO requests to the host, based on the
hardware segments in the request and on any COW blocks covered by the request.

The ubd IO thread is gone, since there is now an equivalent thread in the AIO
module.

There is provision for multiple outstanding requests now.  Requests aren't
retired until all pieces of it have been completed.  The AIO requests have a
shared count, which is decremented as IO operations come in until it reaches
0.  This can be possibly moved to the request struct - haven't looked at this
yet.
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/um/drivers/Makefile

@@ -13,7 +13,7 @@ mcast-objs := mcast_kern.o mcast_user.o
 net-objs := net_kern.o net_user.o
 mconsole-objs := mconsole_kern.o mconsole_user.o
 hostaudio-objs := hostaudio_kern.o
-ubd-objs := ubd_kern.o ubd_user.o
+ubd-objs := ubd_kern.o
 port-objs := port_kern.o port_user.o
 harddog-objs := harddog_kern.o harddog_user.o
 

arch/um/include/aio.h

@@ -14,15 +14,27 @@ struct aio_thread_reply {
 };
 
 struct aio_context {
+	enum aio_type type;
+	int fd;
+	void *data;
+	int len;
+	unsigned long long offset;
 	int reply_fd;
 	struct aio_context *next;
 };
 
+#define INIT_AIO(aio_type, aio_fd, aio_data, aio_len, aio_offset, \
+		 aio_reply_fd) \
+	{ .type 	= aio_type, \
+	  .fd		= aio_fd, \
+	  .data		= aio_data, \
+	  .len		= aio_len, \
+	  .offset	= aio_offset, \
+	  .reply_fd	= aio_reply_fd }
+
 #define INIT_AIO_CONTEXT { .reply_fd	= -1, \
 			   .next	= NULL }
 
-extern int submit_aio(enum aio_type type, int fd, char *buf, int len,
-		      unsigned long long offset, int reply_fd,
-                      struct aio_context *aio);
+extern int submit_aio(struct aio_context *aio);
 
 #endif