[PKT_SCHED]: Restore TBF change semantic

When TBF was converted to a classful qdisc, the semantic of the limit
parameter was broken. On initilization an inner bfifo qdisc is created
for backwards compatibility, when changing parameters however the new
limit is ignored and the current child qdisc remains in place.

Always replace the child qdisc by the default bfifo when limit is above
zero, otherwise don't touch the inner qdisc. Current tc version enforce
a limit above zero, other users can avoid creating the inner qdisc by
using zero.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
index e9e473457361f437b9021177acd1f139b17bbb07..d8e03c74ca76f0c0a68159a49d865efe99ec7c74 100644 (file)
--- a/net/sched/sch_tbf.c
+++ b/net/sched/sch_tbf.c
@@ -341,13 +341,14 @@ static int tbf_change(struct Qdisc* sch, struct rtattr *opt)
        if (max_size < 0)
                goto done;
 
-       if (q->qdisc == &noop_qdisc) {
+       if (qopt->limit > 0) {
                if ((child = tbf_create_dflt_qdisc(sch->dev, qopt->limit)) == NULL)
                        goto done;
        }
 
        sch_tree_lock(sch);
-       if (child) q->qdisc = child;
+       if (child)
+               qdisc_destroy(xchg(&q->qdisc, child));
        q->limit = qopt->limit;
        q->mtu = qopt->mtu;
        q->max_size = max_size;