From: Jarek Poplawski <redacted>
Date: Thu, 21 Aug 2008 20:58:57 +0200

sch_tree_lock() should be enough for now because in the current
implementation we have only one root qdisc with pointers copied to
every dev_queue. At least I can't see nothing more in qdisc_create()
and qdisc_graft(). So, qdisc_lookup() seems to be designed for the
future (or to do this lookup more exactly with additional loops...).

Yes, I designed it for the future.

Nothing really uses this capability currently.