selftests/bpf: Add test for dmabuf_iter

This test creates a udmabuf, and a dmabuf from the system dmabuf heap,
and uses a BPF program that prints dmabuf metadata with the new
dmabuf_iter to verify they can be found.

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/20250522230429.941193-5-tjmercier@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 53 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/dmabuf_iter.c b/tools/testing/selftests/bpf/progs/dmabuf_iter.c
new file mode 100644
index 000000000000..e53d7646d07a
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/dmabuf_iter.c
@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Google LLC */
+#include <vmlinux.h>
+#include <bpf/bpf_core_read.h>
+#include <bpf/bpf_helpers.h>
+
+/* From uapi/linux/dma-buf.h */
+#define DMA_BUF_NAME_LEN 32
+
+char _license[] SEC("license") = "GPL";
+
+/*
+ * Fields output by this iterator are delimited by newlines. Convert any
+ * newlines in user-provided printed strings to spaces.
+ */
+static void sanitize_string(char *src, size_t size)
+{
+	for (char *c = src; (size_t)(c - src) < size && *c; ++c)
+		if (*c == '\n')
+			*c = ' ';
+}
+
+SEC("iter/dmabuf")
+int dmabuf_collector(struct bpf_iter__dmabuf *ctx)
+{
+	const struct dma_buf *dmabuf = ctx->dmabuf;
+	struct seq_file *seq = ctx->meta->seq;
+	unsigned long inode = 0;
+	size_t size;
+	const char *pname, *exporter;
+	char name[DMA_BUF_NAME_LEN] = {'\0'};
+
+	if (!dmabuf)
+		return 0;
+
+	if (BPF_CORE_READ_INTO(&inode, dmabuf, file, f_inode, i_ino) ||
+	    bpf_core_read(&size, sizeof(size), &dmabuf->size) ||
+	    bpf_core_read(&pname, sizeof(pname), &dmabuf->name) ||
+	    bpf_core_read(&exporter, sizeof(exporter), &dmabuf->exp_name))
+		return 1;
+
+	/* Buffers are not required to be named */
+	if (pname) {
+		if (bpf_probe_read_kernel(name, sizeof(name), pname))
+			return 1;
+
+		/* Name strings can be provided by userspace */
+		sanitize_string(name, sizeof(name));
+	}
+
+	BPF_SEQ_PRINTF(seq, "%lu\n%llu\n%s\n%s\n", inode, size, name, exporter);
+	return 0;
+}