selftests/bpf: Add mptcp_subflow bpf_iter test prog

This patch adds a ftrace hook for mptcp_sched_get_send() to test the newly
added mptcp_subflow bpf_iter. This test simulates a typical mptcp packet
scheduler, which selects a subflow from multiple subflows of an mptcp
socket to send data.

Export mptcp_subflow helpers bpf_iter_mptcp_subflow_new/_next/_destroy,
bpf_mptcp_sock_acquire/_release and other helpers into bpf_experimental.h.

Use _acquire() to acquire the msk, then use bpf_for_each(mptcp_subflow) to
walk the subflow list of this msk. Invoke kfuncs mptcp_subflow_active() and
bpf_mptcp_subflow_tcp_sock() in the loop to pick a subsocket. Finally use
bpf_mptcp_subflow_ctx() to get the subflow context of this subsocket and
use mptcp_subflow_set_scheduled() to set it as being scheduled.

Signed-off-by: Geliang Tang <[email protected]>

tools/testing/selftests/bpf/bpf_experimental.h

@@ -575,6 +575,13 @@ extern int bpf_iter_css_new(struct bpf_iter_css *it,
 extern struct cgroup_subsys_state *bpf_iter_css_next(struct bpf_iter_css *it) __weak __ksym;
 extern void bpf_iter_css_destroy(struct bpf_iter_css *it) __weak __ksym;
 
+struct bpf_iter_mptcp_subflow;
+extern int bpf_iter_mptcp_subflow_new(struct bpf_iter_mptcp_subflow *it,
+				      struct mptcp_sock *msk) __weak __ksym;
+extern struct mptcp_subflow_context *
+bpf_iter_mptcp_subflow_next(struct bpf_iter_mptcp_subflow *it) __weak __ksym;
+extern void bpf_iter_mptcp_subflow_destroy(struct bpf_iter_mptcp_subflow *it) __weak __ksym;
+
 extern int bpf_wq_init(struct bpf_wq *wq, void *p__map, unsigned int flags) __weak __ksym;
 extern int bpf_wq_start(struct bpf_wq *wq, unsigned int flags) __weak __ksym;
 extern int bpf_wq_set_callback_impl(struct bpf_wq *wq,

tools/testing/selftests/bpf/progs/mptcp_bpf.h

@@ -43,9 +43,18 @@ mptcp_subflow_tcp_sock(const struct mptcp_subflow_context *subflow)
 }
 
 /* ksym */
+extern bool mptcp_subflow_active(struct mptcp_subflow_context *subflow) __ksym;
 extern void mptcp_subflow_set_scheduled(struct mptcp_subflow_context *subflow,
 					bool scheduled) __ksym;
 
+extern struct mptcp_sock *bpf_mptcp_sock_acquire(struct mptcp_sock *msk) __ksym;
+extern void bpf_mptcp_sock_release(struct mptcp_sock *msk) __ksym;
+
+extern struct mptcp_subflow_context *
+bpf_mptcp_subflow_ctx(const struct sock *sk) __ksym;
+extern struct sock *
+bpf_mptcp_subflow_tcp_sock(const struct mptcp_subflow_context *subflow) __ksym;
+
 extern struct mptcp_subflow_context *
 bpf_mptcp_subflow_ctx_by_pos(const struct mptcp_sched_data *data, unsigned int pos) __ksym;
 

tools/testing/selftests/bpf/progs/mptcp_bpf_iters_subflow.c

@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024, Kylin Software */
+
+/* vmlinux.h, bpf_helpers.h and other 'define' */
+#include "bpf_tracing_net.h"
+#include "mptcp_bpf.h"
+
+char _license[] SEC("license") = "GPL";
+int subflows;
+int pid;
+
+SEC("fentry/mptcp_sched_get_send")
+int BPF_PROG(trace_mptcp_sched_get_send, struct mptcp_sock *msk)
+{
+	struct mptcp_subflow_context *subflow;
+	struct sock *ssk = NULL;
+
+	if (bpf_get_current_pid_tgid() >> 32 != pid)
+		return 0;
+
+	msk = bpf_mptcp_sock_acquire(msk);
+	if (!msk)
+		return 0;
+	bpf_for_each(mptcp_subflow, subflow, msk) {
+		if (subflow->token != msk->token)
+			break;
+
+		if (!mptcp_subflow_active(subflow))
+			continue;
+
+		ssk = bpf_mptcp_subflow_tcp_sock(subflow);
+	}
+	bpf_mptcp_sock_release(msk);
+
+	if (!ssk)
+		return 0;
+	subflow = bpf_mptcp_subflow_ctx(ssk);
+	mptcp_subflow_set_scheduled(subflow, true);
+	subflows = subflow->subflow_id;
+
+	return 0;
+}