This patch tests the new helper bpf_mptcpify(). Store the new protocol
value after invoking the helper to a local BSS variable.

This is defined in a 'sock_create' SEC, so it will be invoked in
BPF_CGROUP_RUN_PROG_INET_SOCK() in inet_create().

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 tools/testing/selftests/bpf/bpf_tcp_helpers.h |  1 +
 tools/testing/selftests/bpf/progs/mptcpify.c  | 26 +++++++++++++++++++
 2 files changed, 27 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/mptcpify.c

diff --git a/tools/testing/selftests/bpf/bpf_tcp_helpers.h b/tools/testing/selftests/bpf/bpf_tcp_helpers.h
index 72c618037386..f846d5d62529 100644
--- a/tools/testing/selftests/bpf/bpf_tcp_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_tcp_helpers.h
@@ -38,6 +38,7 @@ struct sock {
 #define sk_state		__sk_common.skc_state
 	unsigned long		sk_pacing_rate;
 	__u32			sk_pacing_status; /* see enum sk_pacing */
+	__u16			sk_protocol;
 } __attribute__((preserve_access_index));
 
 struct inet_sock {
diff --git a/tools/testing/selftests/bpf/progs/mptcpify.c b/tools/testing/selftests/bpf/progs/mptcpify.c
new file mode 100644
index 000000000000..f04b186b9c26
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/mptcpify.c
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023, SUSE. */
+
+#include <sys/socket.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_tcp_helpers.h"
+
+char _license[] SEC("license") = "GPL";
+__u16 protocol = 0;
+
+SEC("cgroup/sock_create")
+int sock(struct bpf_sock *ctx)
+{
+	struct sock *sk;
+
+	if (ctx->type != SOCK_STREAM)
+		return 1;
+
+	sk = bpf_mptcpify(ctx);
+	if (!sk)
+		return 1;
+
+	protocol = sk->sk_protocol;
+	return 1;
+}
-- 
2.35.3