This patch implements the setting a subflow as stale/unstale in BPF MPTCP
scheduler, named bpf_stale. The staled subflow id will be added into a
map in sk_storage.

Two helper mptcp_subflow_set_stale() and mptcp_subflow_clear_stale() are
added.

In this test, subflow 1 is set as stale in bpf_stale_data_init(). Each
subflow is checked whether it's a stale one in bpf_stale_get_subflow() to
select a unstale subflow to send data.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 tools/testing/selftests/bpf/bpf_tcp_helpers.h |   1 +
 .../selftests/bpf/progs/mptcp_bpf_stale.c     | 163 ++++++++++++++++++
 2 files changed, 164 insertions(+)
 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 6360593f64a4..4f7a41c8a47a 100644
--- a/tools/testing/selftests/bpf/bpf_tcp_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_tcp_helpers.h
@@ -239,6 +239,7 @@ struct mptcp_subflow_context {
 	unsigned long avg_pacing_rate;
 	__u32	backup : 1;
 	__u8	stale_count;
+	__u32	subflow_id;
 	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..10e56fa07818
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/mptcp_bpf_stale.c
@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023, SUSE. */
+
+#include <linux/bpf.h>
+#include "bpf_tcp_helpers.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct mptcp_stale_storage {
+	__u8 nr;
+	__u32 ids[MPTCP_SUBFLOWS_MAX];
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_SK_STORAGE);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__type(key, int);
+	__type(value, struct mptcp_stale_storage);
+} mptcp_stale_map SEC(".maps");
+
+static void mptcp_subflow_set_stale(struct mptcp_stale_storage *storage,
+				    __u32 subflow_id)
+{
+	if (!subflow_id)
+		return;
+
+	for (int i = 0; i < storage->nr && i < MPTCP_SUBFLOWS_MAX; i++) {
+		if (storage->ids[i] == subflow_id)
+			return;
+	}
+
+	if (storage->nr < MPTCP_SUBFLOWS_MAX - 1)
+		storage->ids[storage->nr++] = subflow_id;
+}
+
+static void mptcp_subflow_clear_stale(struct mptcp_stale_storage *storage,
+				      __u32 subflow_id)
+{
+	if (!subflow_id)
+		return;
+
+	for (int i = 0; i < storage->nr && i < MPTCP_SUBFLOWS_MAX; i++) {
+		if (storage->ids[i] == subflow_id) {
+			for (int j = i; j < MPTCP_SUBFLOWS_MAX - 1; j++) {
+				if (!storage->ids[j + 1])
+					break;
+				storage->ids[j] = storage->ids[j + 1];
+				storage->ids[j + 1] = 0;
+			}
+			storage->nr--;
+			return;
+		}
+	}
+}
+
+static bool mptcp_subflow_is_stale(struct mptcp_stale_storage *storage,
+				   __u32 subflow_id)
+{
+	for (int i = 0; i < storage->nr && i < MPTCP_SUBFLOWS_MAX; i++) {
+		if (storage->ids[i] == subflow_id)
+			return true;
+	}
+
+	return false;
+}
+
+static bool mptcp_subflow_is_active(struct mptcp_sched_data *data,
+				    __u32 subflow_id)
+{
+	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 (subflow->subflow_id == subflow_id)
+			return true;
+	}
+
+	return false;
+}
+
+SEC("struct_ops/mptcp_sched_stale_init")
+void BPF_PROG(mptcp_sched_stale_init, struct mptcp_sock *msk)
+{
+	struct mptcp_stale_storage *storage;
+
+	storage = bpf_sk_storage_get(&mptcp_stale_map, msk, 0,
+				     BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (!storage)
+		return;
+
+	storage->nr = 0;
+}
+
+SEC("struct_ops/mptcp_sched_stale_release")
+void BPF_PROG(mptcp_sched_stale_release, struct mptcp_sock *msk)
+{
+	bpf_sk_storage_delete(&mptcp_stale_map, msk);
+}
+
+void BPF_STRUCT_OPS(bpf_stale_data_init, struct mptcp_sock *msk,
+		    struct mptcp_sched_data *data)
+{
+	struct mptcp_subflow_context *subflow;
+	struct mptcp_stale_storage *storage;
+
+	mptcp_sched_data_set_contexts(msk, data);
+
+	storage = bpf_sk_storage_get(&mptcp_stale_map, msk, 0,
+				     BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (!storage)
+		return;
+
+	for (int i = 0; i < storage->nr && i < MPTCP_SUBFLOWS_MAX; i++) {
+		if (!mptcp_subflow_is_active(data, storage->ids[i]))
+			mptcp_subflow_clear_stale(storage, storage->ids[i]);
+	}
+
+	subflow = mptcp_subflow_ctx_by_pos(data, 1);
+	if (subflow)
+		mptcp_subflow_set_stale(storage, subflow->subflow_id);
+}
+
+int BPF_STRUCT_OPS(bpf_stale_get_subflow, struct mptcp_sock *msk,
+		   const struct mptcp_sched_data *data)
+{
+	struct mptcp_stale_storage *storage;
+	int nr = -1;
+
+	storage = bpf_sk_storage_get(&mptcp_stale_map, msk, 0,
+				     BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (!storage)
+		return -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 (mptcp_subflow_is_stale(storage, subflow->subflow_id))
+			continue;
+
+		nr = i;
+	}
+
+	if (nr != -1) {
+		mptcp_subflow_set_scheduled(mptcp_subflow_ctx_by_pos(data, nr), true);
+		return -1;
+	}
+	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