selftests/bpf: Add bpf_loop test

Add test for bpf_loop testing a variety of cases:
various nr_loops, null callback ctx, invalid flags, nested callbacks.
Signed-off-by: Joanne Koong <joannekoong@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211130030622.4131246-3-joannekoong@fb.com

tools/testing/selftests/bpf/prog_tests/bpf_loop.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include <test_progs.h>
+#include <network_helpers.h>
+#include "bpf_loop.skel.h"
+
+static void check_nr_loops(struct bpf_loop *skel)
+{
+	struct bpf_link *link;
+
+	link = bpf_program__attach(skel->progs.test_prog);
+	if (!ASSERT_OK_PTR(link, "link"))
+		return;
+
+	/* test 0 loops */
+	skel->bss->nr_loops = 0;
+
+	usleep(1);
+
+	ASSERT_EQ(skel->bss->nr_loops_returned, skel->bss->nr_loops,
+		  "0 loops");
+
+	/* test 500 loops */
+	skel->bss->nr_loops = 500;
+
+	usleep(1);
+
+	ASSERT_EQ(skel->bss->nr_loops_returned, skel->bss->nr_loops,
+		  "500 loops");
+	ASSERT_EQ(skel->bss->g_output, (500 * 499) / 2, "g_output");
+
+	/* test exceeding the max limit */
+	skel->bss->nr_loops = -1;
+
+	usleep(1);
+
+	ASSERT_EQ(skel->bss->err, -E2BIG, "over max limit");
+
+	bpf_link__destroy(link);
+}
+
+static void check_callback_fn_stop(struct bpf_loop *skel)
+{
+	struct bpf_link *link;
+
+	link = bpf_program__attach(skel->progs.test_prog);
+	if (!ASSERT_OK_PTR(link, "link"))
+		return;
+
+	/* testing that loop is stopped when callback_fn returns 1 */
+	skel->bss->nr_loops = 400;
+	skel->data->stop_index = 50;
+
+	usleep(1);
+
+	ASSERT_EQ(skel->bss->nr_loops_returned, skel->data->stop_index + 1,
+		  "nr_loops_returned");
+	ASSERT_EQ(skel->bss->g_output, (50 * 49) / 2,
+		  "g_output");
+
+	bpf_link__destroy(link);
+}
+
+static void check_null_callback_ctx(struct bpf_loop *skel)
+{
+	struct bpf_link *link;
+
+	/* check that user is able to pass in a null callback_ctx */
+	link = bpf_program__attach(skel->progs.prog_null_ctx);
+	if (!ASSERT_OK_PTR(link, "link"))
+		return;
+
+	skel->bss->nr_loops = 10;
+
+	usleep(1);
+
+	ASSERT_EQ(skel->bss->nr_loops_returned, skel->bss->nr_loops,
+		  "nr_loops_returned");
+
+	bpf_link__destroy(link);
+}
+
+static void check_invalid_flags(struct bpf_loop *skel)
+{
+	struct bpf_link *link;
+
+	/* check that passing in non-zero flags returns -EINVAL */
+	link = bpf_program__attach(skel->progs.prog_invalid_flags);
+	if (!ASSERT_OK_PTR(link, "link"))
+		return;
+
+	usleep(1);
+
+	ASSERT_EQ(skel->bss->err, -EINVAL, "err");
+
+	bpf_link__destroy(link);
+}
+
+static void check_nested_calls(struct bpf_loop *skel)
+{
+	__u32 nr_loops = 100, nested_callback_nr_loops = 4;
+	struct bpf_link *link;
+
+	/* check that nested calls are supported */
+	link = bpf_program__attach(skel->progs.prog_nested_calls);
+	if (!ASSERT_OK_PTR(link, "link"))
+		return;
+
+	skel->bss->nr_loops = nr_loops;
+	skel->bss->nested_callback_nr_loops = nested_callback_nr_loops;
+
+	usleep(1);
+
+	ASSERT_EQ(skel->bss->nr_loops_returned, nr_loops * nested_callback_nr_loops
+		  * nested_callback_nr_loops, "nr_loops_returned");
+	ASSERT_EQ(skel->bss->g_output, (4 * 3) / 2 * nested_callback_nr_loops
+		* nr_loops, "g_output");
+
+	bpf_link__destroy(link);
+}
+
+void test_bpf_loop(void)
+{
+	struct bpf_loop *skel;
+
+	skel = bpf_loop__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "bpf_loop__open_and_load"))
+		return;
+
+	skel->bss->pid = getpid();
+
+	if (test__start_subtest("check_nr_loops"))
+		check_nr_loops(skel);
+	if (test__start_subtest("check_callback_fn_stop"))
+		check_callback_fn_stop(skel);
+	if (test__start_subtest("check_null_callback_ctx"))
+		check_null_callback_ctx(skel);
+	if (test__start_subtest("check_invalid_flags"))
+		check_invalid_flags(skel);
+	if (test__start_subtest("check_nested_calls"))
+		check_nested_calls(skel);
+
+	bpf_loop__destroy(skel);
+}

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct callback_ctx {
+	int output;
+};
+
+/* These should be set by the user program */
+u32 nested_callback_nr_loops;
+u32 stop_index = -1;
+u32 nr_loops;
+int pid;
+
+/* Making these global variables so that the userspace program
+ * can verify the output through the skeleton
+ */
+int nr_loops_returned;
+int g_output;
+int err;
+
+static int callback(__u32 index, void *data)
+{
+	struct callback_ctx *ctx = data;
+
+	if (index >= stop_index)
+		return 1;
+
+	ctx->output += index;
+
+	return 0;
+}
+
+static int empty_callback(__u32 index, void *data)
+{
+	return 0;
+}
+
+static int nested_callback2(__u32 index, void *data)
+{
+	nr_loops_returned += bpf_loop(nested_callback_nr_loops, callback, data, 0);
+
+	return 0;
+}
+
+static int nested_callback1(__u32 index, void *data)
+{
+	bpf_loop(nested_callback_nr_loops, nested_callback2, data, 0);
+	return 0;
+}
+
+SEC("fentry/__x64_sys_nanosleep")
+int test_prog(void *ctx)
+{
+	struct callback_ctx data = {};
+
+	if (bpf_get_current_pid_tgid() >> 32 != pid)
+		return 0;
+
+	nr_loops_returned = bpf_loop(nr_loops, callback, &data, 0);
+
+	if (nr_loops_returned < 0)
+		err = nr_loops_returned;
+	else
+		g_output = data.output;
+
+	return 0;
+}
+
+SEC("fentry/__x64_sys_nanosleep")
+int prog_null_ctx(void *ctx)
+{
+	if (bpf_get_current_pid_tgid() >> 32 != pid)
+		return 0;
+
+	nr_loops_returned = bpf_loop(nr_loops, empty_callback, NULL, 0);
+
+	return 0;
+}
+
+SEC("fentry/__x64_sys_nanosleep")
+int prog_invalid_flags(void *ctx)
+{
+	struct callback_ctx data = {};
+
+	if (bpf_get_current_pid_tgid() >> 32 != pid)
+		return 0;
+
+	err = bpf_loop(nr_loops, callback, &data, 1);
+
+	return 0;
+}
+
+SEC("fentry/__x64_sys_nanosleep")
+int prog_nested_calls(void *ctx)
+{
+	struct callback_ctx data = {};
+
+	if (bpf_get_current_pid_tgid() >> 32 != pid)
+		return 0;
+
+	nr_loops_returned = 0;
+	bpf_loop(nr_loops, nested_callback1, &data, 0);
+
+	g_output = data.output;
+
+	return 0;
+}