From 8cca39e251718baec13a5999bf3d18c05af865be Mon Sep 17 00:00:00 2001 From: Matthieu Baerts Date: Wed, 2 Feb 2022 17:03:39 -0800 Subject: mptcp: clarify when options can be used RFC8684 doesn't seem to clearly specify which MPTCP options can be used together. Some options are mutually exclusive -- e.g. MP_CAPABLE and MP_JOIN --, some can be used together -- e.g. DSS + MP_PRIO --, some can but we prefer not to -- e.g. DSS + ADD_ADDR -- and some have to be used together at some points -- e.g. MP_FAIL and DSS. We need to clarify this as a base before allowing other modifications. For example, does it make sense to send a RM_ADDR with an MPC or MPJ? This remains open for possible future discussions. Signed-off-by: Matthieu Baerts Signed-off-by: Mat Martineau Signed-off-by: David S. Miller --- net/mptcp/options.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/net/mptcp/options.c b/net/mptcp/options.c index ab054c389a5f..7345f28f3de1 100644 --- a/net/mptcp/options.c +++ b/net/mptcp/options.c @@ -1267,8 +1267,27 @@ void mptcp_write_options(__be32 *ptr, const struct tcp_sock *tp, const struct sock *ssk = (const struct sock *)tp; struct mptcp_subflow_context *subflow; - /* DSS, MPC, MPJ, ADD_ADDR, FASTCLOSE and RST are mutually exclusive, - * see mptcp_established_options*() + /* Which options can be used together? + * + * X: mutually exclusive + * O: often used together + * C: can be used together in some cases + * P: could be used together but we prefer not to (optimisations) + * + * Opt: | MPC | MPJ | DSS | ADD | RM | PRIO | FAIL | FC | + * ------|------|------|------|------|------|------|------|------| + * MPC |------|------|------|------|------|------|------|------| + * MPJ | X |------|------|------|------|------|------|------| + * DSS | X | X |------|------|------|------|------|------| + * ADD | X | X | P |------|------|------|------|------| + * RM | C | C | C | P |------|------|------|------| + * PRIO | X | C | C | C | C |------|------|------| + * FAIL | X | X | C | X | X | X |------|------| + * FC | X | X | X | X | X | X | X |------| + * RST | X | X | X | X | X | X | O | O | + * ------|------|------|------|------|------|------|------|------| + * + * The same applies in mptcp_established_options() function. */ if (likely(OPTION_MPTCP_DSS & opts->suboptions)) { struct mptcp_ext *mpext = &opts->ext_copy; -- cgit