On Wed, 16 Oct 2019 15:42:28 -0700, Cong Wang wrote: > > @@ -612,7 +613,7 @@ static int netem_enqueue(struct sk_buff *skb, struct > > Qdisc *sch, > > } > > segs = skb2; > > } > > - qdisc_tree_reduce_backlog(sch, -nb, prev_len - len); > > + qdisc_tree_reduce_backlog(sch, !skb - nb, prev_len - len); > > Am I the only one has trouble to understand the expression > "!skb - nb"?
The backward logic of qdisc_tree_reduce_backlog() always gives me a pause :S Is -nb + !skb any better? The point is we have a "credit" for the "head" skb we dropped. If we didn't manage to queue any of the segs then the expression becomes ...reduce_backlog(sch, 1, prev_len) basically cleaning up after the head. My knee jerk reaction was -> we should return DROP if head got dropped, but that just makes things more nasty because we requeue the segs directly into netem so if we say DROP we have to special case all the segs which succeeded, that gets even more hairy. I'm open to suggestions.. :(
