selftests/bpf: Add test for open coded dmabuf_iter

Use the same test buffers as the traditional iterator and a new BPF map
to verify the test buffers can be found with the open coded dmabuf
iterator.

Signed-off-by: T.J. Mercier <tjmercier@google.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20250522230429.941193-6-tjmercier@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/bpf_experimental.h

@@ -591,4 +591,9 @@ extern int bpf_iter_kmem_cache_new(struct bpf_iter_kmem_cache *it) __weak __ksym
 extern struct kmem_cache *bpf_iter_kmem_cache_next(struct bpf_iter_kmem_cache *it) __weak __ksym;
 extern void bpf_iter_kmem_cache_destroy(struct bpf_iter_kmem_cache *it) __weak __ksym;
 
+struct bpf_iter_dmabuf;
+extern int bpf_iter_dmabuf_new(struct bpf_iter_dmabuf *it) __weak __ksym;
+extern struct dma_buf *bpf_iter_dmabuf_next(struct bpf_iter_dmabuf *it) __weak __ksym;
+extern void bpf_iter_dmabuf_destroy(struct bpf_iter_dmabuf *it) __weak __ksym;
+
 #endif

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

@@ -219,14 +219,52 @@ static void subtest_dmabuf_iter_check_default_iter(struct dmabuf_iter *skel)
 	close(iter_fd);
 }
 
+static void subtest_dmabuf_iter_check_open_coded(struct dmabuf_iter *skel, int map_fd)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+	char key[DMA_BUF_NAME_LEN];
+	int err, fd;
+	bool found;
+
+	/* No need to attach it, just run it directly */
+	fd = bpf_program__fd(skel->progs.iter_dmabuf_for_each);
+
+	err = bpf_prog_test_run_opts(fd, &topts);
+	if (!ASSERT_OK(err, "test_run_opts err"))
+		return;
+	if (!ASSERT_OK(topts.retval, "test_run_opts retval"))
+		return;
+
+	if (!ASSERT_OK(bpf_map_get_next_key(map_fd, NULL, key), "get next key"))
+		return;
+
+	do {
+		ASSERT_OK(bpf_map_lookup_elem(map_fd, key, &found), "lookup");
+		ASSERT_TRUE(found, "found test buffer");
+	} while (bpf_map_get_next_key(map_fd, key, key));
+}
+
 void test_dmabuf_iter(void)
 {
 	struct dmabuf_iter *skel = NULL;
+	int map_fd;
+	const bool f = false;
 
 	skel = dmabuf_iter__open_and_load();
 	if (!ASSERT_OK_PTR(skel, "dmabuf_iter__open_and_load"))
 		return;
 
+	map_fd = bpf_map__fd(skel->maps.testbuf_hash);
+	if (!ASSERT_OK_FD(map_fd, "map_fd"))
+		goto destroy_skel;
+
+	if (!ASSERT_OK(bpf_map_update_elem(map_fd, udmabuf_test_buffer_name, &f, BPF_ANY),
+		       "insert udmabuf"))
+		goto destroy_skel;
+	if (!ASSERT_OK(bpf_map_update_elem(map_fd, sysheap_test_buffer_name, &f, BPF_ANY),
+		       "insert sysheap buffer"))
+		goto destroy_skel;
+
 	if (!ASSERT_OK(create_test_buffers(), "create_test_buffers"))
 		goto destroy;
 
@@ -237,8 +275,11 @@ void test_dmabuf_iter(void)
 		subtest_dmabuf_iter_check_no_infinite_reads(skel);
 	if (test__start_subtest("default_iter"))
 		subtest_dmabuf_iter_check_default_iter(skel);
+	if (test__start_subtest("open_coded"))
+		subtest_dmabuf_iter_check_open_coded(skel, map_fd);
 
 destroy:
 	destroy_test_buffers();
+destroy_skel:
 	dmabuf_iter__destroy(skel);
 }

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

@@ -9,6 +9,13 @@
 
 char _license[] SEC("license") = "GPL";
 
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(key_size, DMA_BUF_NAME_LEN);
+	__type(value, bool);
+	__uint(max_entries, 5);
+} testbuf_hash SEC(".maps");
+
 /*
  * Fields output by this iterator are delimited by newlines. Convert any
  * newlines in user-provided printed strings to spaces.
@@ -51,3 +58,44 @@ int dmabuf_collector(struct bpf_iter__dmabuf *ctx)
 	BPF_SEQ_PRINTF(seq, "%lu\n%llu\n%s\n%s\n", inode, size, name, exporter);
 	return 0;
 }
+
+SEC("syscall")
+int iter_dmabuf_for_each(const void *ctx)
+{
+	struct dma_buf *d;
+
+	bpf_for_each(dmabuf, d) {
+		char name[DMA_BUF_NAME_LEN];
+		const char *pname;
+		bool *found;
+		long len;
+		int i;
+
+		if (bpf_core_read(&pname, sizeof(pname), &d->name))
+			return 1;
+
+		/* Buffers are not required to be named */
+		if (!pname)
+			continue;
+
+		len = bpf_probe_read_kernel_str(name, sizeof(name), pname);
+		if (len < 0)
+			return 1;
+
+		/*
+		 * The entire name buffer is used as a map key.
+		 * Zeroize any uninitialized trailing bytes after the NUL.
+		 */
+		bpf_for(i, len, DMA_BUF_NAME_LEN)
+			name[i] = 0;
+
+		found = bpf_map_lookup_elem(&testbuf_hash, name);
+		if (found) {
+			bool t = true;
+
+			bpf_map_update_elem(&testbuf_hash, name, &t, BPF_EXIST);
+		}
+	}
+
+	return 0;
+}