On Fri, Jan 22, 2021 at 03:46:49PM +0800, 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. > > To achieve this, I re-implement a new helper bpf_redirect_map_multi() > to accept two maps, the forwarding map and exclude map. The forwarding > map could be DEVMAP or DEVMAP_HASH, but the exclude map *must* be > DEVMAP_HASH to get better performace. 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. Hangbin, before you submit next revision, could you try to apply imperative mood to your commit messages? >From Documentation/process/submitting-patches.rst: <quote> Describe your changes in imperative mood, e.g. "make xyzzy do frotz" instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy to do frotz", as if you are giving orders to the codebase to change its behaviour. </quote> That's the thing I'm trying to remind people internally and it feels like we keep on forgetting about that. Thanks! > > As both bpf_xdp_redirect_map() and this new helpers are using struct > bpf_redirect_info, I add a new ex_map and set tgt_value to NULL in the > new helper to make a difference with bpf_xdp_redirect_map(). > > Also I keep the general data path in net/core/filter.c, the native data > path in kernel/bpf/devmap.c so we can use direct calls to get better > performace. > > [0] https://xdp-project.net/#Handling-multicast > > Signed-off-by: Hangbin Liu <liuhangbin@xxxxxxxxx> >
