4334 Improve ZFS N-way mirror read performance

@@ -20,10 +20,11 @@
  */
 
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 Steven Hartland. All rights reserved.
  */
 
 #ifndef _SYS_VDEV_H
 #define _SYS_VDEV_H
 

@@ -116,10 +117,13 @@
 
 extern void vdev_queue_init(vdev_t *vd);
 extern void vdev_queue_fini(vdev_t *vd);
 extern zio_t *vdev_queue_io(zio_t *zio);
 extern void vdev_queue_io_done(zio_t *zio);
+extern int vdev_queue_length(vdev_t *vd);
+extern uint64_t vdev_queue_last_queued_offset(vdev_t *vd);
+extern void vdev_queue_register_last_queued_offset(vdev_t *vd, zio_t *zio);
 
 extern void vdev_config_dirty(vdev_t *vd);
 extern void vdev_config_clean(vdev_t *vd);
 extern int vdev_config_sync(vdev_t **svd, int svdcount, uint64_t txg,
     boolean_t);