On Mon, Sep 14, 2020 at 11:21 AM Song Liu <song@xxxxxxxxxx> wrote: > > On Fri, Sep 11, 2020 at 8:07 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> > > --- > > include/uapi/linux/bpf.h | 1 + > > net/core/filter.c | 9 ++++++++- > > tools/include/uapi/linux/bpf.h | 1 + > > 3 files changed, 10 insertions(+), 1 deletion(-) > > > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > > index 7dd314176df7..7d179eada1c3 100644 > > --- a/include/uapi/linux/bpf.h > > +++ b/include/uapi/linux/bpf.h > > @@ -4060,6 +4060,7 @@ struct bpf_tcp_sock { > > __u32 delivered; /* Total data packets delivered incl. rexmits */ > > __u32 delivered_ce; /* Like the above but only ECE marked packets */ > > __u32 icsk_retransmits; /* Number of unrecovered [RTO] timeouts */ > > + __u32 is_mptcp; /* Is MPTCP subflow? */ > > Shall we have an __u32 flags, and make is_mptcp a bit of it? > Bitfields are slow and more annoying to rewrite in verifier, so having an __u32 field is actually good. > Thanks, > Song > [...]
