On Fri, Sep 18, 2020 at 5:13 AM Nicolas Rybowski <nicolas.rybowski@xxxxxxxxxxxx> wrote: > > is_mptcp is a field from struct tcp_sock used to indicate that the > current tcp_sock is part of the MPTCP protocol. > > In this protocol, a first socket (mptcp_sock) is created with > sk_protocol set to IPPROTO_MPTCP (=262) for control purpose but it > isn't directly on the wire. This is the role of the subflow (kernel) > sockets which are classical tcp_sock with sk_protocol set to > IPPROTO_TCP. The only way to differentiate such sockets from plain TCP > sockets is the is_mptcp field from tcp_sock. > > Such an exposure in BPF is thus required to be able to differentiate > plain TCP sockets from MPTCP subflow sockets in BPF_PROG_TYPE_SOCK_OPS > programs. > > The choice has been made to silently pass the case when CONFIG_MPTCP is > unset by defaulting is_mptcp to 0 in order to make BPF independent of > the MPTCP configuration. Another solution is to make the verifier fail > in 'bpf_tcp_sock_is_valid_ctx_access' but this will add an additional > '#ifdef CONFIG_MPTCP' in the BPF code and a same injected BPF program > will not run if MPTCP is not set. > > An example use-case is provided in > https://github.com/multipath-tcp/mptcp_net-next/tree/scripts/bpf/examples > > Suggested-by: Matthieu Baerts <matthieu.baerts@xxxxxxxxxxxx> > Acked-by: Matthieu Baerts <matthieu.baerts@xxxxxxxxxxxx> > Acked-by: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx> > Signed-off-by: Nicolas Rybowski <nicolas.rybowski@xxxxxxxxxxxx> Acked-by: Song Liu <songliubraving@xxxxxx> [...]
