On Fri, May 31, 2019 at 3:01 PM Davide Caratti [off-list ref] wrote:

Please note: this loop was here also before this patch (the 'goto again;'
line is only patch context). It has been introduced with commit
2ecba2d1e45b ("net: sched: act_csum: Fix csum calc for tagged packets").

This is exactly why I ask...

quoted

Why do you still need to loop here? tc_skb_pull_vlans() already
contains a loop to pop all vlan tags?

The reason why the loop is here is:
1) in case there is a stripped vlan tag, it replaces tc_skb_protocol(skb)
with the inner ethertype (i.e. skb->protocol)

2) in case there is one or more unstripped VLAN tags, it pulls them. At
the last iteration, when it does:

Let me ask it in another way:

The original code, without your patch, has a loop (the "goto again") to
pop all vlan tags.

The code with your patch adds yet another loop (the while loop inside your
tc_skb_pull_vlans()) to pop all vlan tags.

So, after your patch, we have both loops. So, I am confused why we need
these two nested loops to just pop all vlan tags? I think one is sufficient.

quoted

quoted

        }

diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index d4699156974a..382ee69fb1a5 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c

@@ -3300,6 +3300,28 @@ unsigned int tcf_exts_num_actions(struct tcf_exts *exts)
 }
 EXPORT_SYMBOL(tcf_exts_num_actions);

+int tc_skb_pull_vlans(struct sk_buff *skb, unsigned int *hdr_count,
+                     __be16 *proto)

It looks like this function fits better in net/core/skbuff.c, because
I don't see anything TC specific.

Ok, I don't know if other parts of the kernel really need it. Its use
should be combined with tc_skb_protocol(), which is in pkt_sched.h.

But i can move it to skbuff, or elsewhwere, unless somebody disagrees.

quoted

quoted

+{
+       if (skb_vlan_tag_present(skb))
+               *proto = skb->protocol;
+
+       while (eth_type_vlan(*proto)) {
+               struct vlan_hdr *vlan;
+
+               if (unlikely(!pskb_may_pull(skb, VLAN_HLEN)))
+                       return -ENOMEM;
+
+               vlan = (struct vlan_hdr *)skb->data;
+               *proto = vlan->h_vlan_encapsulated_proto;
+               skb_pull(skb, VLAN_HLEN);
+               skb_reset_network_header(skb);

Again, this code was in act_csum.c also before. The only intention of this
patch is to ensure that pskb_may_pull() is called before skb_pull(), as
per Eric suggestion, and move this code out of act_csum to use it with
other TC actions.

Sure, no one says the code before yours is more correct, right? :)

quoted

Any reason not to call __skb_vlan_pop() directly?

I think we can't use __skb_vlan_pop(), because 'act_csum' needs to read
the innermost ethertype in the packet to understand if it's IPv4, IPv6 or
else (ARP, EAPOL, ...).

If I well read __skb_vlan_pop(), it returns the VLAN ID, which is useless
here.

I am confused, this could be checked by eth_type_vlan(skb->protocol),
right? So why it stops you from considering __skb_vlan_pop() or
skb_vlan_pop()? They both should return error or zero, not vlan ID.

Thanks.