netdev - Re: [PATCH net-next 3/3] openvswitch: New MPLS actions for layer 2 tunnelling

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Date:   Wed, 11 Dec 2019 20:19:08 -0800
From:   Pravin Shelar <pshelar@....org>
To:     Martin Varghese <martinvarghesenokia@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>, scott.drennan@...ia.com,
        Jiri Benc <jbenc@...hat.com>,
        "Varghese, Martin (Nokia - IN/Bangalore)" <martin.varghese@...ia.com>
Subject: Re: [PATCH net-next 3/3] openvswitch: New MPLS actions for layer 2 tunnelling

On Wed, Dec 11, 2019 at 7:39 AM Martin Varghese
<martinvarghesenokia@...il.com> wrote:
>
> On Tue, Dec 10, 2019 at 10:15:19PM -0800, Pravin Shelar wrote:
> > On Tue, Dec 10, 2019 at 4:02 PM Martin Varghese
> > <martinvarghesenokia@...il.com> wrote:
> > >
> > > On Tue, Dec 10, 2019 at 01:22:56PM -0800, Pravin Shelar wrote:
> > > > On Tue, Dec 10, 2019 at 12:17 AM Martin Varghese
> > > > <martinvarghesenokia@...il.com> wrote:
> > > > >
> > > > > From: Martin Varghese <martin.varghese@...ia.com>
> > > > >
> > > > > The existing PUSH MPLS & POP MPLS actions inserts & removes MPLS header
> > > > > between ethernet header and the IP header. Though this behaviour is fine
> > > > > for L3 VPN where an IP packet is encapsulated inside a MPLS tunnel, it
> > > > > does not suffice the L2 VPN (l2 tunnelling) requirements. In L2 VPN
> > > > > the MPLS header should encapsulate the ethernet packet.
> > > > >
> > > > > The new mpls actions PTAP_PUSH_MPLS & PTAP_POP_MPLS inserts and removes
> > > > > MPLS header from start of the packet respectively.
> > > > >
> > > > > PTAP_PUSH_MPLS - Inserts MPLS header at the start of the packet.
> > > > > @ethertype - Ethertype of MPLS header.
> > > > >
> > > > > PTAP_POP_MPLS - Removes MPLS header from the start of the packet.
> > > > > @ethertype - Ethertype of next header following the popped MPLS header.
> > > > >              Value 0 in ethertype indicates the tunnelled packet is
> > > > >              ethernet.
> > > > >
> > > > Did you considered using existing MPLS action to handle L2 tunneling
> > > > packet ? It can be done by adding another parameter to the MPLS
> > > > actions.
> > >
> >
> > >
> > >
> > > Not really.
> > >
> > > Are you suggesting to extend the ovs_action_push_mpls and similarly for pop
> > >
> > > struct ovs_action_push_mpls {
> > >         __be32 mpls_lse;
> > >         __be16 mpls_ethertype; /* Either %ETH_P_MPLS_UC or %ETH_P_MPLS_MC */
> > > +        bool l2_tunnel;
> > > };
> > >
> > > Does not that break the compatibilty with the existing userspace
> > > OVS ?
> > >
> > Right, extending this would not look good. I am fine with new action.
> > But we can design this new action as superset of existing and PTAP
> > functionality, This way in future we can deprecate existing MPLS
> > action in favor of new action.
> > I think if you add mac_len parameter for the action it would take case
> > of both cases.
> Yes i guess so.
> On the similar lines i guess we dont need a new PTAP_POP action as the existing
> pop action pops mpls header from the start of the packet if the skb->mac_len=0
> We just neeed a add a special handling for ethertype 0 is the existing pop
> implementation

Passing next_proto as zero to skb_mpls_pop() would set skb->protocol
to zero. That does not look good. Lets pass mac_len and next_proto for
both Push and Pop action. I am also fine using using boolean to
distinguish between L2 and L3 case. In that case we are dependent on
skb->mac_len.