[PATCH net-next] mptcp: sockopt: implement IPV6_TCLASS

[PATCH net-next] mptcp: sockopt: implement IPV6_TCLASS

[David 'equinox' Lamparter]

The IPV6_TCLASS setsockopt just needs to be forwarded to the individual
TCP sockets, like IP_TOS is already handled for IPv4.  The code here is
pretty much identical, except there's no helper for IPv6 like IPv4's
__ip_sock_set_tos().

Coincidentally, ssh uses this sockopt and prints an error in the middle
of your ongoing SSH session when it doesn't work (very annoying when
doing SCP/SFTP on a multiplexed session.)

Signed-off-by: David 'equinox' Lamparter <equinox@diac24.net>
Cc: Matthieu Baerts <matttbe@kernel.org>
Cc: Mat Martineau <martineau@kernel.org>
Cc: Geliang Tang <geliang@kernel.org>
---
note: I wasn't entirely sure what tree this should be on top of, with the
mptcp trees on github & kernel.org;  this is on top of net-next.  It
shouldn't really matter though.
---
 net/mptcp/sockopt.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index fcf6feb2a9eb..edddafebb8de 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -394,6 +394,35 @@ static int mptcp_setsockopt_sol_socket(struct mptcp_sock *msk, int optname,
 	return -EOPNOTSUPP;
 }
 
+static int mptcp_setsockopt_v6_set_tclass(struct mptcp_sock *msk, int optname,
+					  sockptr_t optval, unsigned int optlen)
+{
+	struct mptcp_subflow_context *subflow;
+	struct sock *sk = (struct sock *)msk;
+	int err, val;
+
+	err = ipv6_setsockopt(sk, SOL_IPV6, optname, optval, optlen);
+
+	if (err != 0)
+		return err;
+
+	lock_sock(sk);
+	sockopt_seq_inc(msk);
+	val = READ_ONCE(inet6_sk(sk)->tclass);
+	mptcp_for_each_subflow(msk, subflow) {
+		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
+		bool slow;
+
+		slow = lock_sock_fast(ssk);
+		inet6_sk(ssk)->tclass = val;
+		sk_dst_reset(ssk);
+		unlock_sock_fast(ssk, slow);
+	}
+	release_sock(sk);
+
+	return 0;
+}
+
 static int mptcp_setsockopt_v6(struct mptcp_sock *msk, int optname,
 			       sockptr_t optval, unsigned int optlen)
 {
@@ -436,6 +465,8 @@ static int mptcp_setsockopt_v6(struct mptcp_sock *msk, int optname,
 
 		release_sock(sk);
 		break;
+	case IPV6_TCLASS:
+		return mptcp_setsockopt_v6_set_tclass(msk, optname, optval, optlen);
 	}
 
 	return ret;
@@ -1485,6 +1516,9 @@ static int mptcp_getsockopt_v6(struct mptcp_sock *msk, int optname,
 	struct sock *sk = (void *)msk;
 
 	switch (optname) {
+	case IPV6_TCLASS:
+		return mptcp_put_int_option(msk, optval, optlen,
+					    READ_ONCE(inet6_sk(sk)->tclass));
 	case IPV6_V6ONLY:
 		return mptcp_put_int_option(msk, optval, optlen,
 					    sk->sk_ipv6only);
-- 
2.53.0

Re: [PATCH net-next] mptcp: sockopt: implement IPV6_TCLASS

[kernel test robot]

Hi David,

kernel test robot noticed the following build errors:

[auto build test ERROR on net-next/main]

url:    https://github.com/intel-lab-lkp/linux/commits/David-equinox-Lamparter/mptcp-sockopt-implement-IPV6_TCLASS/20260713-162825
base:   net-next/main
patch link:    https://lore.kernel.org/r/20260713080634.296011-1-equinox%40diac24.net
patch subject: [PATCH net-next] mptcp: sockopt: implement IPV6_TCLASS
config: sparc-randconfig-001 (https://download.01.org/0day-ci/archive/20260713/202607132109.n8GCw6cD-lkp@intel.com/config)
compiler: sparc-linux-gcc (GCC) 16.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260713/202607132109.n8GCw6cD-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202607132109.n8GCw6cD-lkp@intel.com/

All errors (new ones prefixed by >>):

   sparc-linux-ld: net/mptcp/sockopt.o: in function `mptcp_setsockopt_v6':
>> sockopt.c:(.text+0x908): undefined reference to `ipv6_setsockopt'

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH net-next] mptcp: sockopt: implement IPV6_TCLASS

[David 'equinox' Lamparter]

On Mon, Jul 13, 2026 at 09:24:52PM +0800, kernel test robot wrote:
>    sparc-linux-ld: net/mptcp/sockopt.o: in function `mptcp_setsockopt_v6':
> >> sockopt.c:(.text+0x908): undefined reference to `ipv6_setsockopt'

Oops.  Forgot IPv6 can still be disabled.  v2 in a few minutes.

Re: [PATCH net-next] mptcp: sockopt: implement IPV6_TCLASS

[kernel test robot]

Hi David,

kernel test robot noticed the following build errors:

[auto build test ERROR on net-next/main]

url:    https://github.com/intel-lab-lkp/linux/commits/David-equinox-Lamparter/mptcp-sockopt-implement-IPV6_TCLASS/20260713-162825
base:   net-next/main
patch link:    https://lore.kernel.org/r/20260713080634.296011-1-equinox%40diac24.net
patch subject: [PATCH net-next] mptcp: sockopt: implement IPV6_TCLASS
config: x86_64-kexec (https://download.01.org/0day-ci/archive/20260713/202607131605.i02odG4b-lkp@intel.com/config)
compiler: clang version 22.1.8 (https://github.com/llvm/llvm-project ca7933e47d3a3451d81e72ac174dcb5aa28b59d1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260713/202607131605.i02odG4b-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202607131605.i02odG4b-lkp@intel.com/

All errors (new ones prefixed by >>):

>> ld.lld: error: undefined symbol: ipv6_setsockopt
   >>> referenced by sockopt.c:404 (net/mptcp/sockopt.c:404)
   >>>               vmlinux.o:(mptcp_setsockopt)

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki