On Wed, Dec 31, 2014 at 4:15 AM, Cong Wang [off-list ref] wrote:

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

quoted

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.

Thanks Cong, got it. The device will use the noop_qdisc when it's not
activated yet...

BTW, do you have some methods to recommend if I want to find the
initial codes that introduce the noop_qdisc first in the kernel? I
tried to search the LKML archives and google, but seems it's not easy
to do that

-- 
Den