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mptcp: monitor: add 'deny join id0' info

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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) <matttbe@kernel.org>
Signed-off-by: David Ahern <dsahern@kernel.org>
This commit is contained in:
Matthieu Baerts (NGI0) 2025-11-24 12:19:25 +01:00 committed by David Ahern
parent 18e46e8180
commit 9beba226b9
1 changed files with 10 additions and 2 deletions
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12
ip/ipmptcp.c
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@ -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);