extern boolean_t zfs_nocacheflush;
extern int vdev_open(vdev_t *);
+extern void vdev_open_children(vdev_t *vd);
extern int vdev_validate(vdev_t *);
extern void vdev_close(vdev_t *);
extern int vdev_create(vdev_t *, uint64_t txg, boolean_t isreplace);