Add an auxiliary subroutine to generate read(2) event while testing.

Reviewed by:	gnn, ngie
Differential Revision:	https://reviews.freebsd.org/D11673

cddl/contrib/opensolaris/cmd/dtrace/test/tst/common/dtraceUtil/tst.DestructWithFunction.d.ksh

@@ -38,6 +38,14 @@
 ##
 
 
+reader()
+{
+	while true
+	do
+		sleep 0.1
+		cat /etc/motd > /dev/null
+	done
+}
 
 if [ $# != 1 ]; then
 	echo expected one argument: '<'dtrace-path'>'
@@ -46,6 +54,9 @@ fi
 
 dtrace=$1
 
+reader &
+child=$!
+
 $dtrace -qwf read'{chill(15); printf("Done chilling"); exit(0);}'
 status=$?
 
@@ -53,4 +64,6 @@ if [ "$status" -ne 0 ]; then
 	echo $tst: dtrace failed
 fi
 
+kill $child
+
 exit $status