[PATCH bpf-next 7/8] selftests/bpf: add hashmap test for bpf_for_each_map_elem() helper

[Yonghong Song <yhs@fb.com>]

A test case is added for hashmap and percpu hashmap. The test
also exercises nested bpf_for_each_map_elem() calls like
    bpf_prog:
      bpf_for_each_map_elem(func1)
    func1:
      bpf_for_each_map_elem(func2)
    func2:

  $ ./test_progs -n 44
  #44/1 hash_map:OK
  #44 for_each:OK
  Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Yonghong Song <yhs@fb.com>
---
 .../selftests/bpf/prog_tests/for_each.c       |  91 ++++++++++++++++
 .../bpf/progs/for_each_hash_map_elem.c        | 103 ++++++++++++++++++
 2 files changed, 194 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/for_each.c
 create mode 100644 tools/testing/selftests/bpf/progs/for_each_hash_map_elem.c

diff --git a/tools/testing/selftests/bpf/prog_tests/for_each.c b/tools/testing/selftests/bpf/prog_tests/for_each.c
new file mode 100644
index 000000000000..7a399fbc89a4
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/for_each.c
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include <test_progs.h>
+#include "for_each_hash_map_elem.skel.h"
+
+static int duration;
+
+static void do_dummy_read(struct bpf_program *prog)
+{
+	struct bpf_link *link;
+	char buf[16] = {};
+	int iter_fd, len;
+
+	link = bpf_program__attach_iter(prog, NULL);
+	if (CHECK(IS_ERR(link), "attach_iter", "attach_iter failed\n"))
+		return;
+
+	iter_fd = bpf_iter_create(bpf_link__fd(link));
+	if (CHECK(iter_fd < 0, "create_iter", "create_iter failed\n"))
+		goto free_link;
+
+	/* not check contents, but ensure read() ends without error */
+	while ((len = read(iter_fd, buf, sizeof(buf))) > 0)
+		;
+	CHECK(len < 0, "read", "read failed: %s\n", strerror(errno));
+
+	close(iter_fd);
+
+free_link:
+	bpf_link__destroy(link);
+}
+
+static void test_hash_map(void)
+{
+	int i, hashmap_fd, percpu_map_fd, err;
+	struct for_each_hash_map_elem *skel;
+	__u64 *percpu_valbuf = NULL;
+	__u32 key, num_cpus;
+	__u64 val;
+
+	skel = for_each_hash_map_elem__open_and_load();
+	if (CHECK(!skel, "for_each_hash_map_elem__open_and_load",
+		  "skeleton open_and_load failed\n"))
+		return;
+
+	hashmap_fd = bpf_map__fd(skel->maps.hashmap);
+	for (i = 0; i < bpf_map__max_entries(skel->maps.hashmap); i++) {
+		key = i;
+		val = i + 1;
+		err = bpf_map_update_elem(hashmap_fd, &key, &val, BPF_ANY);
+		if (CHECK(err, "map_update", "map_update failed\n"))
+			goto out;
+	}
+
+	num_cpus = bpf_num_possible_cpus();
+	percpu_map_fd = bpf_map__fd(skel->maps.percpu_map);
+	percpu_valbuf = malloc(sizeof(__u64) * num_cpus);
+	if (CHECK_FAIL(!percpu_valbuf))
+		goto out;
+
+	key = 1;
+	for (i = 0; i < num_cpus; i++)
+		percpu_valbuf[i] = i + 1;
+	err = bpf_map_update_elem(percpu_map_fd, &key, percpu_valbuf, BPF_ANY);
+	if (CHECK(err, "percpu_map_update", "map_update failed\n"))
+		goto out;
+
+	do_dummy_read(skel->progs.dump_task);
+
+	ASSERT_EQ(skel->bss->called, 1, "called");
+	ASSERT_EQ(skel->bss->hashmap_output, 4, "output_val");
+
+	key = 1;
+	err = bpf_map_lookup_elem(hashmap_fd, &key, &val);
+	ASSERT_ERR(err, "hashmap_lookup");
+
+	ASSERT_EQ(skel->bss->percpu_called, 1, "percpu_called");
+	CHECK_FAIL(skel->bss->cpu >= num_cpus);
+	ASSERT_EQ(skel->bss->percpu_key, 1, "percpu_key");
+	ASSERT_EQ(skel->bss->percpu_val, skel->bss->cpu + 1, "percpu_val");
+	ASSERT_EQ(skel->bss->percpu_output, 100, "percpu_output");
+out:
+	free(percpu_valbuf);
+	for_each_hash_map_elem__destroy(skel);
+}
+
+void test_for_each(void)
+{
+	if (test__start_subtest("hash_map"))
+		test_hash_map();
+}
diff --git a/tools/testing/selftests/bpf/progs/for_each_hash_map_elem.c b/tools/testing/selftests/bpf/progs/for_each_hash_map_elem.c
new file mode 100644
index 000000000000..7808a5aa75e7
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/for_each_hash_map_elem.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include "bpf_iter.h"
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 3);
+	__type(key, __u32);
+	__type(value, __u64);
+} hashmap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERCPU_HASH);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u64);
+} percpu_map SEC(".maps");
+
+struct callback_ctx {
+	struct bpf_iter__task *ctx;
+	int input;
+	int output;
+};
+
+static __u64
+check_hash_elem(struct bpf_map *map, __u32 *key, __u64 *val,
+		struct callback_ctx *data)
+{
+	struct bpf_iter__task *ctx = data->ctx;
+	__u32 k;
+	__u64 v;
+
+	if (ctx) {
+		k = *key;
+		v = *val;
+		if (ctx->meta->seq_num == 10 && k == 10 && v == 10)
+			data->output = 3; /* impossible path */
+		else
+			data->output = 4;
+	} else {
+		data->output = data->input;
+		bpf_map_delete_elem(map, key);
+	}
+
+	return 0;
+}
+
+__u32 cpu = 0;
+__u32 percpu_called = 0;
+__u32 percpu_key = 0;
+__u64 percpu_val = 0;
+
+static __u64
+check_percpu_elem(struct bpf_map *map, __u32 *key, __u64 *val,
+		  struct callback_ctx *data)
+{
+	percpu_called++;
+	cpu = bpf_get_smp_processor_id();
+	percpu_key = *key;
+	percpu_val = *val;
+
+	bpf_for_each_map_elem(&hashmap, check_hash_elem, data, 0);
+	return 0;
+}
+
+int called = 0;
+int hashmap_output = 0;
+int percpu_output = 0;
+
+SEC("iter/task")
+int dump_task(struct bpf_iter__task *ctx)
+{
+	struct seq_file *seq =  ctx->meta->seq;
+	struct task_struct *task = ctx->task;
+	struct callback_ctx data;
+	int ret;
+
+	/* only call once since we will delete map elements */
+	if (task == (void *)0 || called > 0)
+		return 0;
+
+	called++;
+
+	data.ctx = ctx;
+	data.input = task->tgid;
+	data.output = 0;
+	ret = bpf_for_each_map_elem(&hashmap, check_hash_elem, &data, 0);
+	if (ret)
+		return 0;
+
+	hashmap_output = data.output;
+
+	data.ctx = 0;
+	data.input = 100;
+	data.output = 0;
+	bpf_for_each_map_elem(&percpu_map, check_percpu_elem, &data, 0);
+	percpu_output = data.output;
+
+	return 0;
+}
-- 
2.24.1