selftests/bpf: Add libbpf feature-probing API selftests

Add selftests for prog/map/prog+helper feature probing APIs. Prog and
map selftests are designed in such a way that they will always test all
the possible prog/map types, based on running kernel's vmlinux BTF enum
definition. This way we'll always be sure that when adding new BPF
program types or map types, libbpf will be always updated accordingly to
be able to feature-detect them.

BPF prog_helper selftest will have to be manually extended with
interesting and important prog+helper combinations, it's easy, but can't
be completely automated.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/bpf/20211217171202.3352835-3-andrii@kernel.org

tools/testing/selftests/bpf/config

@@ -38,7 +38,9 @@ CONFIG_IPV6_SIT=m
 CONFIG_BPF_JIT=y
 CONFIG_BPF_LSM=y
 CONFIG_SECURITY=y
+CONFIG_RC_CORE=y
 CONFIG_LIRC=y
+CONFIG_BPF_LIRC_MODE2=y
 CONFIG_IMA=y
 CONFIG_SECURITYFS=y
 CONFIG_IMA_WRITE_POLICY=y

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

+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2021 Facebook */
+
+#include <test_progs.h>
+#include <bpf/btf.h>
+
+void test_libbpf_probe_prog_types(void)
+{
+	struct btf *btf;
+	const struct btf_type *t;
+	const struct btf_enum *e;
+	int i, n, id;
+
+	btf = btf__parse("/sys/kernel/btf/vmlinux", NULL);
+	if (!ASSERT_OK_PTR(btf, "btf_parse"))
+		return;
+
+	/* find enum bpf_prog_type and enumerate each value */
+	id = btf__find_by_name_kind(btf, "bpf_prog_type", BTF_KIND_ENUM);
+	if (!ASSERT_GT(id, 0, "bpf_prog_type_id"))
+		goto cleanup;
+	t = btf__type_by_id(btf, id);
+	if (!ASSERT_OK_PTR(t, "bpf_prog_type_enum"))
+		goto cleanup;
+
+	for (e = btf_enum(t), i = 0, n = btf_vlen(t); i < n; e++, i++) {
+		const char *prog_type_name = btf__str_by_offset(btf, e->name_off);
+		enum bpf_prog_type prog_type = (enum bpf_prog_type)e->val;
+		int res;
+
+		if (prog_type == BPF_PROG_TYPE_UNSPEC)
+			continue;
+
+		if (!test__start_subtest(prog_type_name))
+			continue;
+
+		res = libbpf_probe_bpf_prog_type(prog_type, NULL);
+		ASSERT_EQ(res, 1, prog_type_name);
+	}
+
+cleanup:
+	btf__free(btf);
+}
+
+void test_libbpf_probe_map_types(void)
+{
+	struct btf *btf;
+	const struct btf_type *t;
+	const struct btf_enum *e;
+	int i, n, id;
+
+	btf = btf__parse("/sys/kernel/btf/vmlinux", NULL);
+	if (!ASSERT_OK_PTR(btf, "btf_parse"))
+		return;
+
+	/* find enum bpf_map_type and enumerate each value */
+	id = btf__find_by_name_kind(btf, "bpf_map_type", BTF_KIND_ENUM);
+	if (!ASSERT_GT(id, 0, "bpf_map_type_id"))
+		goto cleanup;
+	t = btf__type_by_id(btf, id);
+	if (!ASSERT_OK_PTR(t, "bpf_map_type_enum"))
+		goto cleanup;
+
+	for (e = btf_enum(t), i = 0, n = btf_vlen(t); i < n; e++, i++) {
+		const char *map_type_name = btf__str_by_offset(btf, e->name_off);
+		enum bpf_map_type map_type = (enum bpf_map_type)e->val;
+		int res;
+
+		if (map_type == BPF_MAP_TYPE_UNSPEC)
+			continue;
+
+		if (!test__start_subtest(map_type_name))
+			continue;
+
+		res = libbpf_probe_bpf_map_type(map_type, NULL);
+		ASSERT_EQ(res, 1, map_type_name);
+	}
+
+cleanup:
+	btf__free(btf);
+}
+
+void test_libbpf_probe_helpers(void)
+{
+#define CASE(prog, helper, supp) {			\
+	.prog_type_name = "BPF_PROG_TYPE_" # prog,	\
+	.helper_name = "bpf_" # helper,			\
+	.prog_type = BPF_PROG_TYPE_ ## prog,		\
+	.helper_id = BPF_FUNC_ ## helper,		\
+	.supported = supp,				\
+}
+	const struct case_def {
+		const char *prog_type_name;
+		const char *helper_name;
+		enum bpf_prog_type prog_type;
+		enum bpf_func_id helper_id;
+		bool supported;
+	} cases[] = {
+		CASE(KPROBE, unspec, false),
+		CASE(KPROBE, map_lookup_elem, true),
+		CASE(KPROBE, loop, true),
+
+		CASE(KPROBE, ktime_get_coarse_ns, false),
+		CASE(SOCKET_FILTER, ktime_get_coarse_ns, true),
+
+		CASE(KPROBE, sys_bpf, false),
+		CASE(SYSCALL, sys_bpf, true),
+	};
+	size_t case_cnt = ARRAY_SIZE(cases), i;
+	char buf[128];
+
+	for (i = 0; i < case_cnt; i++) {
+		const struct case_def *d = &cases[i];
+		int res;
+
+		snprintf(buf, sizeof(buf), "%s+%s", d->prog_type_name, d->helper_name);
+
+		if (!test__start_subtest(buf))
+			continue;
+
+		res = libbpf_probe_bpf_helper(d->prog_type, d->helper_id, NULL);
+		ASSERT_EQ(res, d->supported, buf);
+	}
+}