[PATCH mptcp-next v7 6/9] mptcp: handle SO_ZEROCOPY in setsockopt

From: Geliang Tang <[email protected]>

SO_ZEROCOPY is currently rejected by MPTCP setsockopt with
-EOPNOTSUPP, even though the matching MSG_ZEROCOPY path in
mptcp_sendmsg() is wired up. As a result MSG_ZEROCOPY silently
falls back to a copy on MPTCP sockets because the opt-in flag
is never set.

Expose SO_ZEROCOPY through the SOL_SOCKET setsockopt dispatcher.
The new mptcp_setsockopt_sol_socket_zerocopy() helper validates
that val is 0 or 1 (matching standard TCP sk_setsockopt) and flips
SOCK_ZEROCOPY on the msk only. mptcp_sendmsg() consults the same
flag directly, so opt-in is honoured on every data path without
any cross-socket propagation.

Signed-off-by: Geliang Tang <[email protected]>
---
 net/mptcp/sockopt.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index fcf6feb2a9eb..abcc7d4452b4 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -175,6 +175,19 @@ static int mptcp_setsockopt_sol_socket_tstamp(struct mptcp_sock *msk, int optnam
 	return 0;
 }
 
+static int mptcp_setsockopt_sol_socket_zerocopy(struct mptcp_sock *msk, int val)
+{
+	struct sock *sk = (struct sock *)msk;
+
+	if (val != 0 && val != 1)
+		return -EINVAL;
+
+	lock_sock(sk);
+	sock_valbool_flag(sk, SOCK_ZEROCOPY, val);
+	release_sock(sk);
+	return 0;
+}
+
 static int mptcp_setsockopt_sol_socket_int(struct mptcp_sock *msk, int optname,
 					   sockptr_t optval,
 					   unsigned int optlen)
@@ -203,6 +216,8 @@ static int mptcp_setsockopt_sol_socket_int(struct mptcp_sock *msk, int optname,
 	case SO_TIMESTAMPNS_OLD:
 	case SO_TIMESTAMPNS_NEW:
 		return mptcp_setsockopt_sol_socket_tstamp(msk, optname, val);
+	case SO_ZEROCOPY:
+		return mptcp_setsockopt_sol_socket_zerocopy(msk, val);
 	}
 
 	return -ENOPROTOOPT;
@@ -342,6 +357,7 @@ static int mptcp_setsockopt_sol_socket(struct mptcp_sock *msk, int optname,
 	case SO_TIMESTAMP_NEW:
 	case SO_TIMESTAMPNS_OLD:
 	case SO_TIMESTAMPNS_NEW:
+	case SO_ZEROCOPY:
 		return mptcp_setsockopt_sol_socket_int(msk, optname, optval,
 						       optlen);
 	case SO_TIMESTAMPING_OLD:
@@ -387,7 +403,6 @@ static int mptcp_setsockopt_sol_socket(struct mptcp_sock *msk, int optname,
 	 * SO_CNX_ADVICE is currently unsupported, could possibly be relevant,
 	 * but likely needs careful design
 	 *
-	 * SO_ZEROCOPY is currently unsupported, TODO in sndmsg
 	 * SO_TXTIME is currently unsupported
 	 */
 
-- 
2.53.0