[PATCH v2 1/3] ipv6: extract and export ip6_sock_set_tclass helpers

[Geliang Tang]

From: Geliang Tang <tanggeliang at kylinos.cn>

IPV6_TCLASS handling in do_ipv6_setsockopt() inlines the same ECN mask
logic and inet6_sk(sk)->tclass write that callers need when propagating
a tclass value onto a newly created socket.

Pull this into small helpers __ip6_sock_set_tclass()/ip6_sock_set_tclass()
exported via <net/ipv6.h>, so external modules can apply IPV6_TCLASS
without duplicating the ECN handling.

__ip6_sock_set_tclass() will be used by MPTCP's sockopt implementation
(similar to __ip_sock_set_tos), while ip6_sock_set_tclass() will be used
by nvme-tcp (similar to ip_sock_set_tos).

Signed-off-by: Geliang Tang <tanggeliang at kylinos.cn>
---
 include/net/ipv6.h       |  3 +++
 net/ipv6/ipv6_sockglue.c | 31 +++++++++++++++++++++++--------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 3de07e738538..82e57b34ba57 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -1252,6 +1252,9 @@ static inline void ip6_sock_set_recverr(struct sock *sk)
 	inet6_set_bit(RECVERR6, sk);
 }
 
+void __ip6_sock_set_tclass(struct sock *sk, int val);
+void ip6_sock_set_tclass(struct sock *sk, int val);
+
 #define IPV6_PREFER_SRC_MASK (IPV6_PREFER_SRC_TMP | IPV6_PREFER_SRC_PUBLIC | \
 			      IPV6_PREFER_SRC_COA)
 
diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index b4c977434c2e..c59f25fbb336 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -373,6 +373,28 @@ static int ipv6_set_opt_hdr(struct sock *sk, int optname, sockptr_t optval,
 	return err;
 }
 
+void __ip6_sock_set_tclass(struct sock *sk, int val)
+{
+	u8 old_tclass = inet6_sk(sk)->tclass;
+
+	if (sk->sk_type == SOCK_STREAM) {
+		val &= ~INET_ECN_MASK;
+		val |= old_tclass & INET_ECN_MASK;
+	}
+	if (old_tclass != val) {
+		WRITE_ONCE(inet6_sk(sk)->tclass, val);
+		sk_dst_reset(sk);
+	}
+}
+
+void ip6_sock_set_tclass(struct sock *sk, int val)
+{
+	sockopt_lock_sock(sk);
+	__ip6_sock_set_tclass(sk, val);
+	sockopt_release_sock(sk);
+}
+EXPORT_SYMBOL(ip6_sock_set_tclass);
+
 int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 		       sockptr_t optval, unsigned int optlen)
 {
@@ -713,14 +735,7 @@ int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 		/* RFC 3542, 6.5: default traffic class of 0x0 */
 		if (val == -1)
 			val = 0;
-		if (sk->sk_type == SOCK_STREAM) {
-			val &= ~INET_ECN_MASK;
-			val |= np->tclass & INET_ECN_MASK;
-		}
-		if (np->tclass != val) {
-			np->tclass = val;
-			sk_dst_reset(sk);
-		}
+		__ip6_sock_set_tclass(sk, val);
 		retv = 0;
 		break;
 
-- 
2.53.0