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

From: Martin Varghese <[email-masked]>
Date: Thu, 12 Dec 2019 21:32:26 +0530

On Wed, Dec 11, 2019 at 08:19:08PM -0800, Pravin Shelar wrote:
> On Wed, Dec 11, 2019 at 7:39 AM Martin Varghese
> <[email-masked]> 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
> > > <[email-masked]> 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
> > > > > <[email-masked]> wrote:
> > > > > >
> > > > > > From: Martin Varghese <[email-masked]>
> > > > > >
> > > > > > 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.

But setting to zero may be appropriate ? (a kind of reset of the protocol)
Normally skb->protocol holds the ethertype, but in this case we have a ethernet
header after the MPLS header and we need to read that ethernet header to 
find the ethertype.
Also if we decide the caller has to pass the ethertype as it is in normal pop
along with a l2 flag, which ethertype the skb_mpls_pop caller will pass.

Or should the caller pass the trans ether bridging ethertype 0x6558.In that 
case we may not need a flag, but i am not sure if using 0x6558 is correct here.