Re: [PATCH v2 net-next] Enhanced skb_mpls_pop to update ethertype of the packet in all the cases when an ethernet header is present is the packet.

[Martin Varghese <martinvarghesenokia@gmail.com>]

On Sun, Nov 24, 2019 at 09:32:21PM -0800, Pravin Shelar wrote:
> On Sat, Nov 23, 2019 at 2:35 AM Martin Varghese
> <martinvarghesenokia@gmail.com> wrote:
> >
> > From: Martin Varghese <martin.varghese@nokia.com>
> >
> > The skb_mpls_pop was not updating ethertype of an ethernet packet if the
> > packet was originally received from a non ARPHRD_ETHER device.
> >
> > In the below OVS data path flow, since the device corresponding to port 7
> > is an l3 device (ARPHRD_NONE) the skb_mpls_pop function does not update
> > the ethertype of the packet even though the previous push_eth action had
> > added an ethernet header to the packet.
> >
> > recirc_id(0),in_port(7),eth_type(0x8847),
> > mpls(label=12/0xfffff,tc=0/0,ttl=0/0x0,bos=1/1),
> > actions:push_eth(src=00:00:00:00:00:00,dst=00:00:00:00:00:00),
> > pop_mpls(eth_type=0x800),4
> >
> > Signed-off-by: Martin Varghese <martin.varghese@nokia.com>
> > ---
> > Changes in v2:
> >     - check for dev type removed while updating ethertype
> >       in function skb_mpls_pop.
> >     - key->mac_proto is checked in function pop_mpls to pass
> >       ethernt flag to skb_mpls_pop.
> >     - dev type is checked in function tcf_mpls_act to pass
> >       ethernet flag to skb_mpls_pop.
> >
> >  include/linux/skbuff.h    | 3 ++-
> >  net/core/skbuff.c         | 7 ++++---
> >  net/openvswitch/actions.c | 4 +++-
> >  net/sched/act_mpls.c      | 4 +++-
> >  4 files changed, 12 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > index dfe02b6..70204b9 100644
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -3530,7 +3530,8 @@ int skb_zerocopy(struct sk_buff *to, struct sk_buff *from,
> >  int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci);
> >  int skb_mpls_push(struct sk_buff *skb, __be32 mpls_lse, __be16 mpls_proto,
> >                   int mac_len);
> > -int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto, int mac_len);
> > +int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto, int mac_len,
> > +                bool ethernet);
> >  int skb_mpls_update_lse(struct sk_buff *skb, __be32 mpls_lse);
> >  int skb_mpls_dec_ttl(struct sk_buff *skb);
> >  struct sk_buff *pskb_extract(struct sk_buff *skb, int off, int to_copy,
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index 867e61d..988eefb 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -5529,12 +5529,13 @@ int skb_mpls_push(struct sk_buff *skb, __be32 mpls_lse, __be16 mpls_proto,
> >   * @skb: buffer
> >   * @next_proto: ethertype of header after popped MPLS header
> >   * @mac_len: length of the MAC header
> > - *
> > + * @ethernet: flag to indicate if ethernet header is present in packet
> >   * Expects skb->data at mac header.
> >   *
> >   * Returns 0 on success, -errno otherwise.
> >   */
> > -int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto, int mac_len)
> > +int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto, int mac_len,
> > +                bool ethernet)
> >  {
> >         int err;
> >
> > @@ -5553,7 +5554,7 @@ int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto, int mac_len)
> >         skb_reset_mac_header(skb);
> >         skb_set_network_header(skb, mac_len);
> >
> > -       if (skb->dev && skb->dev->type == ARPHRD_ETHER) {
> > +       if (ethernet) {
> >                 struct ethhdr *hdr;
> >
> >                 /* use mpls_hdr() to get ethertype to account for VLANs. */
> > diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> > index 12936c1..264c3c0 100644
> > --- a/net/openvswitch/actions.c
> > +++ b/net/openvswitch/actions.c
> > @@ -179,7 +179,9 @@ static int pop_mpls(struct sk_buff *skb, struct sw_flow_key *key,
> >  {
> >         int err;
> >
> > -       err = skb_mpls_pop(skb, ethertype, skb->mac_len);
> > +       err = skb_mpls_pop(skb, ethertype, skb->mac_len,
> > +                          (key->mac_proto & ~SW_FLOW_KEY_INVALID)
> > +                           == MAC_PROTO_ETHERNET);
> >         if (err)
> >                 return err;
> >
> Why you are not using ovs_key_mac_proto() here?
>

ovs_key_mac_proto returns u8  (supposedly enum sw_flow_mac_proto)

The new skb_mpls_pop takes bool as the last argument.
int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto, int mac_len,
                 bool ethernet)

But if I change the new prototype to take u8(enum sw_flow_mac_proto) as the last argument

I need to make the generic skb_mpls_pop code aware of enum sw_flow_mac_proto defined in Openvswitch/flow.h .

-  if (ethernet) {
+ if(ethernet == MAC_PROTO_ETHERNET)
                struct ethhdr *hdr;

                /* use mpls_hdr() to get ethertype to account for VLANs. */
                hdr = (struct ethhdr *)((void *)mpls_hdr(skb) - ETH_HLEN);
                skb_mod_eth_type(skb, hdr, next_proto);
        }
        skb->protocol = next_proto;

Also ,it means at all the places where skb_mpls_pop is used, this Openvswitch header file (Openvswitch/flow.h)
has to be included, which I assume is not clean.
 
> > diff --git a/net/sched/act_mpls.c b/net/sched/act_mpls.c
> > index 4d8c822..f919f95 100644
> > --- a/net/sched/act_mpls.c
> > +++ b/net/sched/act_mpls.c
> > @@ -13,6 +13,7 @@
> >  #include <net/pkt_sched.h>
> >  #include <net/pkt_cls.h>
> >  #include <net/tc_act/tc_mpls.h>
> > +#include <linux/if_arp.h>
> >
> >  static unsigned int mpls_net_id;
> >  static struct tc_action_ops act_mpls_ops;
> > @@ -76,7 +77,8 @@ static int tcf_mpls_act(struct sk_buff *skb, const struct tc_action *a,
> >
> >         switch (p->tcfm_action) {
> >         case TCA_MPLS_ACT_POP:
> > -               if (skb_mpls_pop(skb, p->tcfm_proto, mac_len))
> > +               if (skb_mpls_pop(skb, p->tcfm_proto, mac_len,
> > +                                (skb->dev && skb->dev->type == ARPHRD_ETHER)))
> >                         goto drop;
> >                 break;
> >         case TCA_MPLS_ACT_PUSH:
> > --
> > 1.8.3.1
> >