This patch implements the setting of stale flag in BPF MPTCP scheduler,
named bpf_stale. The stale flag will be set in bpf_stale_data_init() and
will be checked in bpf_stale_get_subflow().

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 tools/testing/selftests/bpf/bpf_tcp_helpers.h |  3 +-
 .../selftests/bpf/progs/mptcp_bpf_stale.c     | 63 +++++++++++++++++++
 2 files changed, 65 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/progs/mptcp_bpf_stale.c

diff --git a/tools/testing/selftests/bpf/bpf_tcp_helpers.h b/tools/testing/selftests/bpf/bpf_tcp_helpers.h
index 945dd46c98c0..c749940c9103 100644
--- a/tools/testing/selftests/bpf/bpf_tcp_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_tcp_helpers.h
@@ -234,7 +234,8 @@ extern void tcp_cong_avoid_ai(struct tcp_sock *tp, __u32 w, __u32 acked) __ksym;
 #define MPTCP_SUBFLOWS_MAX	8
 
 struct mptcp_subflow_context {
-	__u32	backup : 1;
+	__u32	backup : 1,
+		stale : 1;
 	struct	sock *tcp_sock;	    /* tcp sk backpointer */
 } __attribute__((preserve_access_index));
 
diff --git a/tools/testing/selftests/bpf/progs/mptcp_bpf_stale.c b/tools/testing/selftests/bpf/progs/mptcp_bpf_stale.c
new file mode 100644
index 000000000000..e8cc2e0c24b9
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/mptcp_bpf_stale.c
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023, SUSE. */
+
+#include <linux/bpf.h>
+#include "bpf_tcp_helpers.h"
+
+char _license[] SEC("license") = "GPL";
+
+extern void mptcp_subflow_set_stale(struct mptcp_subflow_context *subflow,
+				    int stale) __ksym;
+
+SEC("struct_ops/mptcp_sched_stale_init")
+void BPF_PROG(mptcp_sched_stale_init, struct mptcp_sock *msk)
+{
+}
+
+SEC("struct_ops/mptcp_sched_stale_release")
+void BPF_PROG(mptcp_sched_stale_release, struct mptcp_sock *msk)
+{
+}
+
+void BPF_STRUCT_OPS(bpf_stale_data_init, struct mptcp_sock *msk,
+		    struct mptcp_sched_data *data)
+{
+	struct mptcp_subflow_context *subflow;
+
+	mptcp_sched_data_set_contexts(msk, data);
+	subflow = mptcp_subflow_ctx_by_pos(data, 1);
+	if (subflow)
+		mptcp_subflow_set_stale(subflow, 1);
+}
+
+int BPF_STRUCT_OPS(bpf_stale_get_subflow, struct mptcp_sock *msk,
+		   const struct mptcp_sched_data *data)
+{
+	int nr = -1;
+
+	for (int i = 0; i < data->subflows && i < MPTCP_SUBFLOWS_MAX; i++) {
+		struct mptcp_subflow_context *subflow;
+
+		subflow = mptcp_subflow_ctx_by_pos(data, i);
+		if (!subflow)
+			break;
+
+		if (BPF_CORE_READ_BITFIELD_PROBED(subflow, stale))
+			continue;
+
+		nr = i;
+	}
+
+	if (nr != -1)
+		mptcp_subflow_set_scheduled(mptcp_subflow_ctx_by_pos(data, nr), true);
+	return 0;
+}
+
+SEC(".struct_ops")
+struct mptcp_sched_ops stale = {
+	.init		= (void *)mptcp_sched_stale_init,
+	.release	= (void *)mptcp_sched_stale_release,
+	.data_init	= (void *)bpf_stale_data_init,
+	.get_subflow	= (void *)bpf_stale_get_subflow,
+	.name		= "bpf_stale",
+};
-- 
2.35.3