On Fri, 2019-05-31 at 11:38 -0700, Cong Wang wrote:
> On Fri, May 31, 2019 at 10:26 AM Davide Caratti <dcara...@redhat.com> wrote:
> > diff --git a/net/sched/act_csum.c b/net/sched/act_csum.c
> > index 14bb525e355e..e8308ddcae9d 100644
> > --- a/net/sched/act_csum.c
> > +++ b/net/sched/act_csum.c
> > @@ -574,7 +574,6 @@ static int tcf_csum_act(struct sk_buff *skb, const
> > struct tc_action *a,
> > struct tcf_result *res)
> > {
> > struct tcf_csum *p = to_tcf_csum(a);
> > - bool orig_vlan_tag_present = false;
> > unsigned int vlan_hdr_count = 0;
> > struct tcf_csum_params *params;
> > u32 update_flags;
> > @@ -604,17 +603,8 @@ static int tcf_csum_act(struct sk_buff *skb, const
> > struct tc_action *a,
> > break;
> > case cpu_to_be16(ETH_P_8021AD): /* fall through */
> > case cpu_to_be16(ETH_P_8021Q):
> > - if (skb_vlan_tag_present(skb) && !orig_vlan_tag_present) {
> > - protocol = skb->protocol;
> > - orig_vlan_tag_present = true;
> > - } else {
> > - struct vlan_hdr *vlan = (struct vlan_hdr
> > *)skb->data;
> > -
> > - protocol = vlan->h_vlan_encapsulated_proto;
> > - skb_pull(skb, VLAN_HLEN);
> > - skb_reset_network_header(skb);
> > - vlan_hdr_count++;
> > - }
> > + if (tc_skb_pull_vlans(skb, &vlan_hdr_count, &protocol))
> > + goto drop;
> > goto again;
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").
> 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:
goto again;
'protocol' contains the innermost ethertype, read from
'h_vlan_encapsulated_proto'.
If that value is 0x0800 (IPv4) or 0x86dd (IPv6), 'act_csum' will go on
computing the internet checksum for the IPv4 header or for (some of the)
IPv6 'nexthdrs'.
(yes, we could move the call to tc_skb_pull_vlans() before the switch
statement to make this code more understandable, also in the other 2
actions. Please let me know if you think it's better).
>
> > }
> >
> > 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.
>
> > +{
> > + 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.
> 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.
>
> > + (*hdr_count)++;
> > + }
> > + return 0;
> > +}
>
> Thanks.
Thanks for reviewing, looking forward to read more comments from you!
