linux-kernel - [PATCH v2 2/2] bpf: add test for DEVMAP reuse

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Message-ID: <20250813200912.3523279-3-yuka@yuka.dev>
Date: Wed, 13 Aug 2025 22:09:11 +0200
From: Yureka Lilian <yuka@...a.dev>
To: Andrii Nakryiko <andrii@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>
Cc: Yureka Lilian <yuka@...a.dev>,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] bpf: add test for DEVMAP reuse

The test covers basic re-use of a pinned DEVMAP map,
with both matching and mismatching parameters.

Signed-off-by: Yureka Lilian <yuka@...a.dev>
---
 .../bpf/prog_tests/pinning_devmap_reuse.c     | 68 +++++++++++++++++++
 .../selftests/bpf/progs/test_pinning_devmap.c | 20 ++++++
 2 files changed, 88 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/pinning_devmap_reuse.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_pinning_devmap.c

diff --git a/tools/testing/selftests/bpf/prog_tests/pinning_devmap_reuse.c b/tools/testing/selftests/bpf/prog_tests/pinning_devmap_reuse.c
new file mode 100644
index 000000000..06befb03b
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/pinning_devmap_reuse.c
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <test_progs.h>
+
+void test_pinning_devmap_reuse(void)
+{
+	const char *pinpath1 = "/sys/fs/bpf/pinmap1";
+	const char *pinpath2 = "/sys/fs/bpf/pinmap2";
+	const char *file = "./test_pinning_devmap.bpf.o";
+	struct bpf_object *obj1 = NULL, *obj2 = NULL;
+	int err;
+	__u32 duration = 0;
+	DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts);
+
+	/* load the object a first time */
+	obj1 = bpf_object__open_file(file, NULL);
+	err = libbpf_get_error(obj1);
+	if (CHECK(err, "first open", "err %d\n", err)) {
+		obj1 = NULL;
+		goto out;
+	}
+	err = bpf_object__load(obj1);
+	if (CHECK(err, "first load", "err %d\n", err))
+		goto out;
+
+	/* load the object a second time, re-using the pinned map */
+	obj2 = bpf_object__open_file(file, NULL);
+	if (CHECK(err, "second open", "err %d\n", err)) {
+		obj2 = NULL;
+		goto out;
+	}
+	err = bpf_object__load(obj2);
+	if (CHECK(err, "second load", "err %d\n", err))
+		goto out;
+
+	/* we can close the reference safely without
+	 * the map's refcount falling to 0
+	 */
+	bpf_object__close(obj1);
+	obj1 = NULL;
+
+	/* now, swap the pins */
+	err = renameat2(0, pinpath1, 0, pinpath2, RENAME_EXCHANGE);
+	if (CHECK(err, "swap pins", "err %d\n", err))
+		goto out;
+
+	/* load the object again, this time the re-use should fail */
+	obj1 = bpf_object__open_file(file, NULL);
+	err = libbpf_get_error(obj1);
+	if (CHECK(err, "third open", "err %d\n", err)) {
+		obj1 = NULL;
+		goto out;
+	}
+	err = bpf_object__load(obj1);
+	if (CHECK(err != -EINVAL, "param mismatch load", "err %d\n", err))
+		goto out;
+
+out:
+	unlink(pinpath1);
+	unlink(pinpath2);
+	if (obj1)
+		bpf_object__close(obj1);
+	if (obj2)
+		bpf_object__close(obj2);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_pinning_devmap.c b/tools/testing/selftests/bpf/progs/test_pinning_devmap.c
new file mode 100644
index 000000000..c855f8f87
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_pinning_devmap.c
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+struct {
+	__uint(type, BPF_MAP_TYPE_DEVMAP);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u32);
+	__uint(pinning, LIBBPF_PIN_BY_NAME);
+} pinmap1 SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_DEVMAP);
+	__uint(max_entries, 2);
+	__type(key, __u32);
+	__type(value, __u32);
+	__uint(pinning, LIBBPF_PIN_BY_NAME);
+} pinmap2 SEC(".maps");
-- 
2.50.1