On Sat, Jun 1, 2019 at 9:22 PM Eli Britstein [off-list ref] wrote:

On 6/1/2019 1:50 AM, Cong Wang wrote:

quoted

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

quoted

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

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.

After Davide's patch, the "goto again" is needed to re-enter the switch
case, and guaranteed to be done only once, as all the VLAN tags were
already pulled. The alternative is having a dedicated if before the switch.

Yeah, I think that can be simply moved before the switch so
that we don't have to use two loops, which should be easier to
understand too.

Thanks.