net: mctp: add MCTP_OPT_ROUTE_SRCADDR getsockopt

include/uapi/linux/mctp.h

@@ -55,6 +55,19 @@ struct mctp_fq_addr {
 #define MCTP_TAG_PREALLOC	0x10
 
 #define MCTP_OPT_ADDR_EXT	1
+#define MCTP_OPT_ROUTE_SRCADDR	2
+
+/* Query structure for MCTP_OPT_ROUTE_SRCADDR getsockopt.
+ *
+ * Caller fills in @net and @daddr before calling getsockopt.
+ * Performs a route lookup and returns the local source EID in @saddr.
+ */
+struct mctp_route_srcaddr {
+	unsigned int	net;
+	mctp_eid_t	daddr;
+	mctp_eid_t	saddr;
+	__u8		__pad[2];
+};
 
 #define SIOCMCTPALLOCTAG	(SIOCPROTOPRIVATE + 0)
 #define SIOCMCTPDROPTAG		(SIOCPROTOPRIVATE + 1)

net/mctp/af_mctp.c

@@ -425,6 +425,39 @@ static int mctp_getsockopt(struct socket *sock, int level, int optname,
 		return 0;
 	}
 
+	if (optname == MCTP_OPT_ROUTE_SRCADDR) {
+		struct mctp_route_srcaddr rsa;
+		struct mctp_dst dst;
+		unsigned int net;
+		int rc;
+
+		if (len != sizeof(rsa))
+			return -EINVAL;
+
+		if (copy_from_user(&rsa, optval, sizeof(rsa)))
+			return -EFAULT;
+
+		net = rsa.net;
+		if (net == MCTP_NET_ANY)
+			net = mctp_default_net(sock_net(sock->sk));
+
+		rc = mctp_route_lookup(sock_net(sock->sk), net, rsa.daddr, &dst);
+		if (rc)
+			return rc;
+
+		rsa.saddr = dst.saddr;
+		mctp_dst_release(&dst);
+
+		if (rsa.saddr == MCTP_ADDR_NULL)
+			return -EADDRNOTAVAIL;
+
+		if (put_user(sizeof(rsa), optlen))
+			return -EFAULT;
+		if (copy_to_user(optval, &rsa, sizeof(rsa)))
+			return -EFAULT;
+		return 0;
+	}
+
 	return -ENOPROTOOPT;
 }
 

net/mctp/test/sock-test.c

@@ -379,10 +379,59 @@ static void mctp_test_assumptions(struct kunit *test)
 	KUNIT_ASSERT_EQ(test, mctp_default_net(&init_net), 1);
 }
 
+static void mctp_test_getsockopt_route_srcaddr(struct kunit *test)
+{
+	struct mctp_route_srcaddr rsa = {
+		.net = MCTP_INITIAL_DEFAULT_NET,
+		.daddr = 9,
+	};
+	struct mctp_test_route *rt;
+	struct mctp_test_dev *dev;
+	struct socket *sock;
+	int optlen = sizeof(rsa);
+	int rc;
+
+	__mctp_sock_test_init(test, &dev, &rt, &sock);
+
+	/* Query the source EID for destination EID 9; the device has
+	 * local EID 8, so the route lookup should return saddr=8.
+	 */
+	rc = mctp_getsockopt(sock, SOL_MCTP, MCTP_OPT_ROUTE_SRCADDR,
+			     (char __user *)&rsa, (int __user *)&optlen);
+	KUNIT_EXPECT_EQ(test, rc, 0);
+	KUNIT_EXPECT_EQ(test, (int)rsa.saddr, 8);
+	KUNIT_EXPECT_EQ(test, optlen, (int)sizeof(rsa));
+
+	__mctp_sock_test_fini(test, dev, rt, sock);
+}
+
+static void mctp_test_getsockopt_route_srcaddr_no_route(struct kunit *test)
+{
+	struct mctp_route_srcaddr rsa = {
+		.net = MCTP_INITIAL_DEFAULT_NET,
+		.daddr = 99,  /* no route for this EID */
+	};
+	struct mctp_test_route *rt;
+	struct mctp_test_dev *dev;
+	struct socket *sock;
+	int optlen = sizeof(rsa);
+	int rc;
+
+	__mctp_sock_test_init(test, &dev, &rt, &sock);
+
+	rc = mctp_getsockopt(sock, SOL_MCTP, MCTP_OPT_ROUTE_SRCADDR,
+			     (char __user *)&rsa, (int __user *)&optlen);
+	KUNIT_EXPECT_EQ(test, rc, -EHOSTUNREACH);
+
+	__mctp_sock_test_fini(test, dev, rt, sock);
+}
+
 static struct kunit_case mctp_test_cases[] = {
 	KUNIT_CASE(mctp_test_assumptions),
 	KUNIT_CASE(mctp_test_sock_sendmsg_extaddr),
 	KUNIT_CASE(mctp_test_sock_recvmsg_extaddr),
+	KUNIT_CASE(mctp_test_getsockopt_route_srcaddr),
+	KUNIT_CASE(mctp_test_getsockopt_route_srcaddr_no_route),
 	KUNIT_CASE_PARAM(mctp_test_bind_conflicts, mctp_bind_pair_gen_params),
 	KUNIT_CASE(mctp_test_bind_invalid),
 	{}