[PATCH bpf-next v3 08/10] selftests/bpf: Add BPF iterator tests for resizable hash map

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

From: Mykyta Yatsenko <yatsenko@meta.com>

Test basic BPF iterator functionality for BPF_MAP_TYPE_RHASH,
verifying all elements are visited.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
---
 tools/testing/selftests/bpf/prog_tests/rhash.c     | 63 ++++++++++++++++++++++
 .../selftests/bpf/progs/bpf_iter_bpf_rhash_map.c   | 34 ++++++++++++
 2 files changed, 97 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/rhash.c b/tools/testing/selftests/bpf/prog_tests/rhash.c
index 0f6eec4fe1fe..7e5a5fbd70c2 100644
--- a/tools/testing/selftests/bpf/prog_tests/rhash.c
+++ b/tools/testing/selftests/bpf/prog_tests/rhash.c
@@ -4,6 +4,7 @@
 #include <string.h>
 #include <stdio.h>
 #include "rhash.skel.h"
+#include "bpf_iter_bpf_rhash_map.skel.h"
 #include <linux/bpf.h>
 #include <linux/perf_event.h>
 #include <sys/syscall.h>
@@ -39,6 +40,65 @@ static void rhash_run(const char *prog_name)
 	rhash__destroy(skel);
 }
 
+static void rhash_iter_test(void)
+{
+	DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts);
+	struct bpf_iter_bpf_rhash_map *skel;
+	int err, i, len, map_fd, iter_fd;
+	union bpf_iter_link_info linfo;
+	u32 expected_key_sum = 0, key;
+	struct bpf_link *link;
+	u64 val = 0;
+	char buf[64];
+
+	skel = bpf_iter_bpf_rhash_map__open();
+	if (!ASSERT_OK_PTR(skel, "bpf_iter_bpf_rhash_map__open"))
+		return;
+
+	err = bpf_iter_bpf_rhash_map__load(skel);
+	if (!ASSERT_OK(err, "bpf_iter_bpf_rhash_map__load"))
+		goto out;
+
+	map_fd = bpf_map__fd(skel->maps.rhashmap);
+
+	/* Populate map with test data */
+	for (i = 0; i < 64; i++) {
+		key = i + 1;
+		expected_key_sum += key;
+
+		err = bpf_map_update_elem(map_fd, &key, &val, BPF_NOEXIST);
+		if (!ASSERT_OK(err, "map_update"))
+			goto out;
+	}
+
+	memset(&linfo, 0, sizeof(linfo));
+	linfo.map.map_fd = map_fd;
+	opts.link_info = &linfo;
+	opts.link_info_len = sizeof(linfo);
+
+	link = bpf_program__attach_iter(skel->progs.dump_bpf_rhash_map, &opts);
+	if (!ASSERT_OK_PTR(link, "attach_iter"))
+		goto out;
+
+	iter_fd = bpf_iter_create(bpf_link__fd(link));
+	if (!ASSERT_GE(iter_fd, 0, "create_iter"))
+		goto free_link;
+
+	do {
+		len = read(iter_fd, buf, sizeof(buf));
+	} while (len > 0);
+
+	ASSERT_EQ(skel->bss->key_sum, expected_key_sum, "key_sum");
+	ASSERT_EQ(skel->bss->elem_count, 64, "elem_count");
+
+	close(iter_fd);
+
+free_link:
+	bpf_link__destroy(link);
+out:
+	bpf_iter_bpf_rhash_map__destroy(skel);
+}
+
 void test_rhash(void)
 {
 	if (test__start_subtest("test_rhash_lookup_update"))
@@ -61,4 +121,7 @@ void test_rhash(void)
 
 	if (test__start_subtest("test_rhash_delete_nonexistent"))
 		rhash_run("test_rhash_delete_nonexistent");
+
+	if (test__start_subtest("test_rhash_iter"))
+		rhash_iter_test();
 }
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_bpf_rhash_map.c b/tools/testing/selftests/bpf/progs/bpf_iter_bpf_rhash_map.c
new file mode 100644
index 000000000000..86f6c0d5eadb
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_bpf_rhash_map.c
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_RHASH);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__uint(max_entries, 64);
+	__type(key, __u32);
+	__type(value, __u64);
+} rhashmap SEC(".maps");
+
+__u32 key_sum = 0;
+__u64 val_sum = 0;
+__u32 elem_count = 0;
+__u32 err = 0;
+
+SEC("iter/bpf_map_elem")
+int dump_bpf_rhash_map(struct bpf_iter__bpf_map_elem *ctx)
+{
+	__u32 *key = ctx->key;
+	__u64 *val = ctx->value;
+
+	if (!key || !val)
+		return 0;
+
+	key_sum += *key;
+	val_sum += *val;
+	elem_count++;
+	return 0;
+}

-- 
2.52.0