Subject: Re: [PATCH 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.

From: Martin Varghese <[email-masked]>
Date: Fri, 22 Nov 2019 10:42:53 +0530

On Thu, Nov 21, 2019 at 06:22:29PM -0800, Pravin Shelar wrote:
> On Thu, Nov 21, 2019 at 4:23 AM Martin Varghese
> <[email-masked]> wrote:
> >
> > From: Martin Varghese <[email-masked]>
> >
> > 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 <[email-masked]>
> > ---
> >  include/linux/skbuff.h    | 3 ++-
> >  net/core/skbuff.c         | 8 +++++---
> >  net/openvswitch/actions.c | 2 +-
> >  net/sched/act_mpls.c      | 2 +-
> >  4 files changed, 9 insertions(+), 6 deletions(-)
> >
> ...
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index 867e61d..8ac377d 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -5529,12 +5529,14 @@ 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
> > + *           ignored for device type ARPHRD_ETHER
> >   * 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 +5555,7 @@ 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 ((skb->dev && skb->dev->type == ARPHRD_ETHER) || ethernet) {
> >                 struct ethhdr *hdr;
> Lets move the dev-type check to caller. That would also avoid one more
> argument to this function.

To have only the ethernet flag check in the function like below ?
 If (ethernet) {
     /*pseudo*/   Update ethertype
 }
And pass the flag to the function considering the device type
Fo example in case of tc.

if (skb_mpls_pop(skb, p->tcfm_proto, mac_len,
                                 (skb->dev && skb->dev->type == ARPHRD_ETHER))).

But how do we avoid an argument here ? I am missing anything ?
> 
> >
> >                 /* use mpls_hdr() to get ethertype to account for VLANs. */
> > diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> > index 12936c1..9e5d274 100644
> > --- a/net/openvswitch/actions.c
> > +++ b/net/openvswitch/actions.c
> > @@ -179,7 +179,7 @@ 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, true);
> >         if (err)
> OVS supports L3 packets, you need to check flow key for type of packet
> (ovs_key_mac_proto()) under process.

Yes I missed that.
        err = skb_mpls_pop(skb, ethertype, skb->mac_len, ovs_key_mac_proto())); ?
       or 
	err = skb_mpls_pop(skb, ethertype, skb->mac_len, key->mac_proto = MAC_PROTO_ETHERNET)

I assume both acheives the same 

Thanks for reviewing

Martin