There is an design problem with the qdisc interface that causes qlen related
bugs
in netem, tbf, and other qdisc's that peek at the top of the queue. The problem
is
that requeue needs to be called from the dequeue function but requeue can fail.
If requeue fails, then the calling qdisc can not properly handle the error. If
it
returns NULL, then the parent's expectation about qlen gets messed up.
Example:
prio (qlen = 1)
skb = netem dequeue
skb = htb dequeue
... decides not to send this skb now
htp requeue(skb) fails
?? what now
--netem.qlen // := 0
return NULL
skb is NULL
at this point prio qlen is 1 but underlying queue's are empty.
My proposal is to require requeue to always succeed and change it to be
void instead of returning int.
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