[PATCH v2] sch_htb: let skb->priority refer to non-leaf class

[Harry Mason <harry.mason@smoothwall.net>]

If the class in skb->priority is not a leaf, apply filters from the
selected class, not the qdisc. This lets netfilter or user space
partially classify the packet.

Signed-off-by: Harry Mason <harry.mason@smoothwall.net>
---

On Thu, 2014-01-16 at 08:25 -0800, Eric Dumazet wrote:
> On Thu, 2014-01-16 at 14:45 +0000, Harry Mason wrote:
> 
>> + /* Start with inner filter chain if a non-leaf class is selected */
>> + if (cl)
>> +     tcf = cl->filter_list;
>> + else
>> +     tcf = q->filter_list;
> 
> Could this break some existing htb setups ?

I think it is unlikely. Setting skb->priority to a non-leaf class would
be equivalent to setting it to the base qdisc. In theory an application
might rely on this if it expects the classes to be dynamic, but adding
a filter could restore the old behaviour.

To me this is intuitively how it should behave, and reproduces what would
happen if a tc filter instead of netfilter had first assigned the
non-leaf class.

> Also we test cl being NULL at line 222, it would be nice to not
> test it again...

Updated below.

 net/sched/sch_htb.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index 717b210..8073d92 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -219,11 +219,15 @@ static struct htb_class *htb_classify(struct sk_buff *skb, struct Qdisc *sch,
 	if (skb->priority == sch->handle)
 		return HTB_DIRECT;	/* X:0 (direct flow) selected */
 	cl = htb_find(skb->priority, sch);
-	if (cl && cl->level == 0)
-		return cl;
+	if (cl) {
+		if (cl->level == 0)
+			return cl;
+		/* Start with inner filter chain if a non-leaf class is selected */
+		tcf = cl->filter_list;
+	} else
+		tcf = q->filter_list;
 
 	*qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
-	tcf = q->filter_list;
 	while (tcf && (result = tc_classify(skb, tcf, &res)) >= 0) {
 #ifdef CONFIG_NET_CLS_ACT
 		switch (result) {
-- 
1.7.10.4