[RFC PATCHv2 bpf-next 0/2] xdp: add dev map multicast support

[Hangbin Liu <liuhangbin@gmail.com>]

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 achieve this, I re-implement a new helper bpf_redirect_map_multi()
to accept two maps, the forwarding map and exclude map. If user
don't want to use exclude map and just want simply stop redirecting back
to ingress device, they can use flag BPF_F_EXCLUDE_INGRESS.

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

v2: Discussed with Jiri, Toke, Jesper, Eelco, we think the v1 is doing
a trick and may make user confused. So let's just add a new helper
to make the implemention more clear.

Hangbin Liu (2):
  xdp: add a new helper for dev map multicast support
  sample/bpf: add xdp_redirect_map_multicast test

 include/linux/bpf.h                       |  20 +++
 include/linux/filter.h                    |   1 +
 include/net/xdp.h                         |   1 +
 include/uapi/linux/bpf.h                  |  23 ++-
 kernel/bpf/devmap.c                       | 114 +++++++++++++++
 kernel/bpf/verifier.c                     |   6 +
 net/core/filter.c                         |  98 ++++++++++++-
 net/core/xdp.c                            |  26 ++++
 samples/bpf/Makefile                      |   3 +
 samples/bpf/xdp_redirect_map_multi.sh     | 124 ++++++++++++++++
 samples/bpf/xdp_redirect_map_multi_kern.c | 100 +++++++++++++
 samples/bpf/xdp_redirect_map_multi_user.c | 170 ++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h            |  23 ++-
 13 files changed, 702 insertions(+), 7 deletions(-)
 create mode 100755 samples/bpf/xdp_redirect_map_multi.sh
 create mode 100644 samples/bpf/xdp_redirect_map_multi_kern.c
 create mode 100644 samples/bpf/xdp_redirect_map_multi_user.c

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2.19.2