Until recently, the 'flags' attribute was not used. This has recently been changed with the introduction of the 'deny_join_id0' flag [1]. This flag is set when a connection is created and the other peer set the 'C' flag in the MP_CAPABLE packets [2]. This flag can be set to tell the other side that the peer will not accept extra subflows requests sent to its initial IP address and port: typically set by a server behind a legacy Layer 4 load balancer. Now, when this flag is set, "deny_join_id0" will be printed instead of "flags=1". Unknown remaining flags will be printed in hexadecimal at the end, e.g. "flags=0x2". Link: https://git.kernel.org/torvalds/c/2293c57484ae [1] Link: https://datatracker.ietf.org/doc/html/rfc8684#section-3.1-20.6 [2] Signed-off-by: Matthieu Baerts (NGI0) --- ip/ipmptcp.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/ip/ipmptcp.c b/ip/ipmptcp.c index aaacc0a5..01f6906f 100644 --- a/ip/ipmptcp.c +++ b/ip/ipmptcp.c @@ -477,6 +477,7 @@ static int mptcp_monitor_msg(struct rtnl_ctrl_data *ctrl, const struct genlmsghdr *ghdr = NLMSG_DATA(n); struct rtattr *tb[MPTCP_ATTR_MAX + 1]; int len = n->nlmsg_len; + __u16 flags = 0; len -= NLMSG_LENGTH(GENL_HDRLEN); if (len < 0) @@ -526,8 +527,6 @@ static int mptcp_monitor_msg(struct rtnl_ctrl_data *ctrl, printf(" backup=%u", rta_getattr_u8(tb[MPTCP_ATTR_BACKUP])); if (tb[MPTCP_ATTR_ERROR]) printf(" error=%u", rta_getattr_u8(tb[MPTCP_ATTR_ERROR])); - if (tb[MPTCP_ATTR_FLAGS]) - printf(" flags=%x", rta_getattr_u16(tb[MPTCP_ATTR_FLAGS])); if (tb[MPTCP_ATTR_TIMEOUT]) printf(" timeout=%u", rta_getattr_u32(tb[MPTCP_ATTR_TIMEOUT])); if (tb[MPTCP_ATTR_IF_IDX]) @@ -539,6 +538,15 @@ static int mptcp_monitor_msg(struct rtnl_ctrl_data *ctrl, if (tb[MPTCP_ATTR_SERVER_SIDE] && rta_getattr_u8(tb[MPTCP_ATTR_SERVER_SIDE])) printf(" server_side"); + if (tb[MPTCP_ATTR_FLAGS]) + flags = rta_getattr_u16(tb[MPTCP_ATTR_FLAGS]); + if (flags & MPTCP_PM_EV_FLAG_DENY_JOIN_ID0) { + flags &= ~MPTCP_PM_EV_FLAG_DENY_JOIN_ID0; + printf(" deny_join_id0"); + } + if (flags) /* remaining bits */ + printf(" flags=0x%x", flags); + puts(""); out: fflush(stdout); -- 2.51.0