On Thu, Oct 10, 2019 at 08:43:52PM +0200, Davide Caratti wrote:
> the following script:
>
> # tc qdisc add dev eth0 clsact
> # tc filter add dev eth0 egress matchall action mpls pop
>
> implicitly makes the kernel drop all packets transmitted by eth0, if they
> don't have a MPLS header. This behavior is uncommon: other encapsulations
> (like VLAN) just let the packet pass unmodified. Since the result of MPLS
> 'pop' operation would be the same regardless of the presence / absence of
> MPLS header(s) in the original packet, we can let skb_mpls_pop() return 0
> when dealing with non-MPLS packets.
>
> Fixes: 2a2ea50870ba ("net: sched: add mpls manipulation actions to TC")
> Signed-off-by: Davide Caratti <dcara...@redhat.com>
Hi Davide,
For the TC use-case I think this is correct for the reasons you explain
above.
For the OVS use-case I also think it is fine because
__ovs_nla_copy_actions() will ensure that MPLS POP only occurs
for packets with an MPLS Ethernet protocol. That is, this condition
should never occur in that use-case.
And it appears that there are no other users of this function.
I think it might be worth adding something about use-cases other than TC
to the changelog, but that aside:
Reviewed-by: Simon Horman <simon.hor...@netronome.com>
> ---
> net/core/skbuff.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 529133611ea2..cd59ccd6da57 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -5536,7 +5536,7 @@ int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto)
> int err;
>
> if (unlikely(!eth_p_mpls(skb->protocol)))
> - return -EINVAL;
> + return 0;
>
> err = skb_ensure_writable(skb, skb->mac_len + MPLS_HLEN);
> if (unlikely(err))
> --
> 2.21.0
>
