[PATCH] TBF: stop qdisc infanticide

[Stephen Hemminger <shemminger@vyatta.com>]

Several netem users have complained that when using TBF for rate control
that any change to TBF parameters destroys the child qdisc. A typical
use is to have a test that sets up netem + TBF then changes bandwidth
setting.  But every time the parameters of TBF are changed it destroys
the child qdisc, requiring reconfiguration. Other qdisc's like HTB
don't do this.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>


--- a/net/sched/sch_tbf.c	2010-05-12 20:41:06.257006386 -0700
+++ b/net/sched/sch_tbf.c	2010-05-12 20:52:35.671216316 -0700
@@ -273,7 +273,11 @@ static int tbf_change(struct Qdisc* sch,
 	if (max_size < 0)
 		goto done;
 
-	if (qopt->limit > 0) {
+	if (q->qdisc) {
+		err = fifo_set_limit(q->qdisc, qopt->limit);
+		if (err)
+			goto done;
+	} else if (qopt->limit > 0) {
 		child = fifo_create_dflt(sch, &bfifo_qdisc_ops, qopt->limit);
 		if (IS_ERR(child)) {
 			err = PTR_ERR(child);