On Tue, Dec 30, 2014 at 1:23 AM, Dennis Chen [off-list ref] wrote:

After google and the code reading, seems this Qdisc instance is only
used for the initialization purpose, I can't find the reason that this
object introduced in the kernel. Does anybody know what the historical
reason is for this invention? the purpose or the benefit for this
Qdisc object?

Not just for initialization, it is kinda a null qdisc when
the previous qdisc gets removed:

        /* ... and graft new one */
        if (qdisc == NULL)
                qdisc = &noop_qdisc;

or the entire device is not activated yet. It guarantees no
packets can be sent out via this qdisc.