On Thu, 25 Apr 2002, Varun Varma wrote:
> From what I can see of the code in register_netdevice (and the wrapper
> regsiter_netdev), no default qdisc is assigned to a device, if it doesn't
> already contain one when these functions are called - not even noop_qdisc.
> The result should be that dev->qdisc == NULL when it get's checked in
> dev_queue_xmit, and thus queuing is altogether ignored for such a device,
> and the skb is sent to the dev->hard_start_xmit function instead.
>
> Maybe I'm missing something here. What kernel version are you using?
Good point! I am using 2.2.18. The register_netdevice() in 2.2.18 has a
dev_init_scheduler() call which initializes the qdiscs to noop_qdisc.
I am going to look at the 2.4 series to see their changes.
> > And the enqueue function for the noop_qdisc is noop_enqueue() which just
> > frees the skb! So where is the actual packet kicked out from?
>
> Two part answer to this:
>
> 1) If device does indeed have a noop_qdisc associated with it, the skb
> would get "lost" in the noop_enqueue function.
>
> 2) Most interfaces, even those configured with good 'ol ifconfig have
> a queueing discipline associated with them. I believe the default is
> pfifo_fast. You can check this by running "ip link show" on you m/c.
> So a "standard" interface configured with ifconfig would still let
> all packets go through!
Now the test for me to do is check if point 2 holds true for 2.2.18
Will get back with the results.
Thanx.
ciao,
Amit
--
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Amit Kucheria
EECS Grad. Research Assistant
University of Kansas @ Lawrence
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