Illumos #2703: add mechanism to report ZFS send progress

Reviewed by: Matt Ahrens <matt@delphix.com>
Reviewed by: Robert Mustacchi <rm@joyent.com>
Reviewed by: Richard Lowe <richlowe@richlowe.net>
Approved by: Eric Schrock <Eric.Schrock@delphix.com>

References:
  https://www.illumos.org/issues/2703

Ported by: Martin Matuska <martin@matuska.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

include/sys/dsl_dataset.h

@@ -21,6 +21,7 @@
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2011 by Delphix. All rights reserved.
+ * Copyright (c) 2012, Joyent, Inc. All rights reserved.
  */
 
 #ifndef	_SYS_DSL_DATASET_H
@@ -150,6 +151,9 @@ typedef struct dsl_dataset {
 	uint64_t ds_reserved;	/* cached refreservation */
 	uint64_t ds_quota;	/* cached refquota */
 
+	kmutex_t ds_sendstream_lock;
+	list_t ds_sendstreams;
+
 	/* Protected by ds_lock; keep at end of struct for better locality */
 	char ds_snapname[MAXNAMELEN];
 } dsl_dataset_t;