selftests/bpf: add selfstest for btf_task_get_cgroup_idbpf_task_get_cgroup_id

This patch adds a selftest for the `bpf_task_get_cgroup_id` kfunc. The
test focuses on the use case of obtaining the cgroup ID of the previous
task in a `sched_switch` tracepoint.

The selftest involves creating a test cgroup, attaching a BPF program
that utilizes the `bpf_task_get_cgroup_id` during a `sched_switch`
tracepoint, and validating that the obtained cgroup ID for the previous
task matches the expected cgroup ID.

#315     task_get_cgroup_id:OK
Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Jose Fernandez <josef@netflix.com>

2 files changed, 88 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/task_get_cgroup_id.c b/tools/testing/selftests/bpf/prog_tests/task_get_cgroup_id.c
new file mode 100644
index 00000000000000..b8c4551195d357
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/task_get_cgroup_id.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright 2024 Netflix, Inc.
+
+#include <test_progs.h>
+#include <cgroup_helpers.h>
+#include "test_task_get_cgroup_id.skel.h"
+#include <unistd.h>
+
+#define TEST_CGROUP "/test-task-get-cgroup-id/"
+
+void test_task_get_cgroup_id(void)
+{
+	struct test_task_get_cgroup_id *skel;
+	int err, fd;
+	pid_t pid;
+	__u64 cgroup_id, expected_cgroup_id;
+	const struct timespec req = {
+		.tv_sec = 1,
+		.tv_nsec = 0,
+	};
+
+	fd = test__join_cgroup(TEST_CGROUP);
+	if (!ASSERT_OK(fd < 0, "test_join_cgroup_TEST_CGROUP"))
+		return;
+
+	skel = test_task_get_cgroup_id__open();
+	if (!ASSERT_OK_PTR(skel, "test_task_get_cgroup_id__open"))
+		goto cleanup;
+
+	err = test_task_get_cgroup_id__load(skel);
+	if (!ASSERT_OK(err, "test_task_get_cgroup_id__load"))
+		goto cleanup;
+
+	err = test_task_get_cgroup_id__attach(skel);
+	if (!ASSERT_OK(err, "test_task_get_cgroup_id__attach"))
+		goto cleanup;
+
+	pid = getpid();
+	expected_cgroup_id = get_cgroup_id(TEST_CGROUP);
+	if (!ASSERT_GT(expected_cgroup_id, 0, "get_cgroup_id"))
+		goto cleanup;
+
+	/* Trigger nanosleep to enter the sched_switch tracepoint */
+	/* The previous task should be this process */
+	syscall(__NR_nanosleep, &req, NULL);
+
+	err = bpf_map_lookup_elem(bpf_map__fd(skel->maps.pid_to_cgid_map), &pid,
+				  &cgroup_id);
+
+	if (!ASSERT_OK(err, "bpf_map_lookup_elem"))
+		goto cleanup;
+
+	ASSERT_EQ(cgroup_id, expected_cgroup_id, "cgroup_id");
+
+cleanup:
+	test_task_get_cgroup_id__destroy(skel);
+	close(fd);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_task_get_cgroup_id.c b/tools/testing/selftests/bpf/progs/test_task_get_cgroup_id.c
new file mode 100644
index 00000000000000..7e6bc008970f20
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_task_get_cgroup_id.c
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright 2024 Netflix, Inc.
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+u64 bpf_task_get_cgroup_id(struct task_struct *task) __ksym;
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 4096);
+	__type(key, __u32);
+	__type(value, __u64);
+} pid_to_cgid_map SEC(".maps");
+
+SEC("tp_btf/sched_switch")
+int BPF_PROG(sched_switch, bool preempt, struct task_struct *prev,
+	     struct task_struct *next)
+{
+	u32 pid = prev->pid;
+	u64 cgroup_id;
+
+	cgroup_id = bpf_task_get_cgroup_id(prev);
+	bpf_map_update_elem(&pid_to_cgid_map, &pid, &cgroup_id, BPF_ANY);
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";