pkt_sched: Add and use qdisc_root() and qdisc_root_lock().

When code wants to lock the qdisc tree state, the logic
operation it's doing is locking the top-level qdisc that
sits of the root of the netdev_queue.

Add qdisc_root_lock() to represent this and convert the
easiest cases.

In order for this to work out in all cases, we have to
hook up the noop_qdisc to a dummy netdev_queue.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 0 deletions

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index bc2a09d..9241782 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -161,6 +161,18 @@ struct tcf_proto
 	struct tcf_proto_ops	*ops;
 };
 
+static inline struct Qdisc *qdisc_root(struct Qdisc *qdisc)
+{
+	return qdisc->dev_queue->qdisc;
+}
+
+static inline spinlock_t *qdisc_root_lock(struct Qdisc *qdisc)
+{
+	struct Qdisc *root = qdisc_root(qdisc);
+
+	return &root->dev_queue->lock;
+}
+
 static inline struct net_device *qdisc_dev(struct Qdisc *qdisc)
 {
 	return qdisc->dev_queue->dev;