libbdev: extended version

This version of libbdev support asynchronous communication,
recovery after driver restarts, and retrying of failed transfer
operations.

lib/libbdev/type.h

@@ -0,0 +1,16 @@
+#ifndef _BDEV_TYPE_H
+#define _BDEV_TYPE_H
+
+typedef struct {
+  bdev_id_t		id;		/* call ID */
+  dev_t			dev;		/* target device number */
+  message		msg;		/* request message */
+  bdev_callback_t	callback;	/* callback function */
+  bdev_param_t		param;		/* callback parameter */
+  int			driver_tries;	/* times retried on driver restarts */
+  int			transfer_tries;	/* times retried on transfer errors */
+  iovec_t		*vec;		/* original vector */
+  iovec_s_t		gvec[1];	/* grant vector */
+} bdev_call_t;
+
+#endif /* _BDEV_TYPE_H */