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Date: Wed, 31 Dec 2014 15:31:42 +0800 From: Dennis Chen <kernel.org.gnu@...il.com> To: Cong Wang <cwang@...pensource.com> Cc: netdev <netdev@...r.kernel.org> Subject: Re: [Question] What's the noop_qdisc introduced for in the kernel? On Wed, Dec 31, 2014 at 4:15 AM, Cong Wang <cwang@...pensource.com> wrote: > On Tue, Dec 30, 2014 at 1:23 AM, Dennis Chen <kernel.org.gnu@...il.com> 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. 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 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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