Hi all, This is a prototype 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. To be able to reuse the existing bpf_redirect_map() helper, we use a containing map-in-map type to store the forwarding and exclude groups. When a map-in-map type is passed to the redirect helper, it will interpret the index as encoding the forwarding group in the upper 16 bits and the exclude group in the lower 16 bits. The enqueue logic will unpack the two halves of the index and perform separate lookups in the containing map. E.g., an index of 0x00010001 will look for the forwarding group at map index 0x10000 and the exclude group at map index 0x1; the application is expected to populate the map accordingly. For this RFC series we are primarily looking for feedback on the concept and API: the example in patch 2 is functional, but not a lot of effort has been made on performance optimisation. Last but not least, thanks a lot to Jiri, Eelco, Toke and Jesper for suggestions and help on implementation. [0] https://xdp-project.net/#Handling-multicast Hangbin Liu (2): xdp: add dev map multicast support sample/bpf: add xdp_redirect_map_multicast test include/linux/bpf.h | 29 ++ include/net/xdp.h | 1 + kernel/bpf/arraymap.c | 2 +- kernel/bpf/devmap.c | 118 +++++++ kernel/bpf/hashtab.c | 2 +- kernel/bpf/verifier.c | 15 +- net/core/filter.c | 69 +++- net/core/xdp.c | 26 ++ samples/bpf/Makefile | 3 + samples/bpf/xdp_redirect_map_multicast.sh | 142 ++++++++ samples/bpf/xdp_redirect_map_multicast_kern.c | 147 +++++++++ samples/bpf/xdp_redirect_map_multicast_user.c | 306 ++++++++++++++++++ 12 files changed, 854 insertions(+), 6 deletions(-) create mode 100755 samples/bpf/xdp_redirect_map_multicast.sh create mode 100644 samples/bpf/xdp_redirect_map_multicast_kern.c create mode 100644 samples/bpf/xdp_redirect_map_multicast_user.c -- 2.19.2
