On Fri, Jul 10, 2020 at 12:37:59AM +0200, Daniel Borkmann wrote: > On 7/9/20 3:30 AM, Hangbin Liu wrote: > > This patch is for xdp multicast support. which has been discussed before[0], > > The goal is to be able to implement an OVS-like data plane in XDP, i.e., > > a software switch that can forward XDP frames to multiple ports. > > > > To achieve this, an application needs to specify a group of interfaces > > to forward a packet to. It is also common to want to exclude one or more > > physical interfaces from the forwarding operation - e.g., to forward a > > packet to all interfaces in the multicast group except the interface it > > arrived on. While this could be done simply by adding more groups, this > > quickly leads to a combinatorial explosion in the number of groups an > > application has to maintain. > > > > To avoid the combinatorial explosion, we propose to include the ability > > to specify an "exclude group" as part of the forwarding operation. This > > needs to be a group (instead of just a single port index), because a > > physical interface can be part of a logical grouping, such as a bond > > device. > > > > Thus, the logical forwarding operation becomes a "set difference" > > operation, i.e. "forward to all ports in group A that are not also in > > group B". This series implements such an operation using device maps to > > represent the groups. This means that the XDP program specifies two > > device maps, one containing the list of netdevs to redirect to, and the > > other containing the exclude list. > > Could you move this description as part of patch 1/3 instead of cover > letter? Mostly given this helps understanding the rationale wrt exclusion > map which is otherwise lacking from just looking at the patch itself. OK, I will > > Assuming you have a bond, how does this look in practice for your mentioned > ovs-like data plane in XDP? The map for 'group A' is shared among all XDP > progs and the map for 'group B' is managed per prog? The BPF_F_EXCLUDE_INGRESS Yes, kind of. Since we have two maps as parameter. The 'group A map'(include map) will be shared between the interfaces in same group/vlan. The 'group B map' (exclude map) is interface specific. Each interface will hold it's own exclude map. As most time each interface only exclude itself, a null map + BPF_F_EXCLUDE_INGRESS should be enough. For bond situation. e.g. A active-backup bond0 with eth1 + eth2 as slaves. If eth1 is active interface, we can add eth2 to the exclude map. > is clear, but how would this look wrt forwarding from a phys dev /to/ the > bond iface w/ XDP? As bond interface doesn't support native XDP, This forwarding only works for physical slave interfaces. For generic xdp, maybe we can forward to bond interface directly, but I haven't tried. > > Also, what about tc BPF helper support for the case where not every device > might have native XDP (but they could still share the maps)? I haven't tried tc BPF. This helper works for both generic and native xdp forwarding. I think it should also works if we load the prog with native xdp mode in one interface and generic xdp mode in another interface, couldn't we? Thanks Hangbin
