Re: [PATCH bpf-next v3 2/3] selftests/bpf: Add overwrite mode test for BPF ring buffer

[Xu Kuohai]

On 10/28/2025 10:47 AM, Andrii Nakryiko wrote:

On Fri, Oct 17, 2025 at 9:04 PM Xu Kuohai <xukuo...@huaweicloud.com> wrote:

From: Xu Kuohai <xukuo...@huawei.com>

Add overwrite mode test for BPF ring buffer. The test creates a BPF ring
buffer in overwrite mode, then repeatedly reserves and commits records
to check if the ring buffer works as expected both before and after
overwriting occurs.

Signed-off-by: Xu Kuohai <xukuo...@huawei.com>
---
  tools/testing/selftests/bpf/Makefile          |  3 +-
  .../selftests/bpf/prog_tests/ringbuf.c        | 64 ++++++++++++
  .../bpf/progs/test_ringbuf_overwrite.c        | 98 +++++++++++++++++++
  3 files changed, 164 insertions(+), 1 deletion(-)
  create mode 100644 tools/testing/selftests/bpf/progs/test_ringbuf_overwrite.c

diff --git a/tools/testing/selftests/bpf/Makefile 
b/tools/testing/selftests/bpf/Makefile
index f00587d4ede6..43d133bf514d 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -498,7 +498,8 @@ LINKED_SKELS := test_static_linked.skel.h 
linked_funcs.skel.h               \

  LSKELS := fexit_sleep.c trace_printk.c trace_vprintk.c map_ptr_kern.c  \
         core_kern.c core_kern_overflow.c test_ringbuf.c                 \
-       test_ringbuf_n.c test_ringbuf_map_key.c test_ringbuf_write.c
+       test_ringbuf_n.c test_ringbuf_map_key.c test_ringbuf_write.c    \
+       test_ringbuf_overwrite.c

  LSKELS_SIGNED := fentry_test.c fexit_test.c atomics.c

diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c 
b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
index d1e4cb28a72c..5264af1dc768 100644
--- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
+++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
@@ -17,6 +17,7 @@
  #include "test_ringbuf_n.lskel.h"
  #include "test_ringbuf_map_key.lskel.h"
  #include "test_ringbuf_write.lskel.h"
+#include "test_ringbuf_overwrite.lskel.h"

  #define EDONE 7777

@@ -497,6 +498,67 @@ static void ringbuf_map_key_subtest(void)
         test_ringbuf_map_key_lskel__destroy(skel_map_key);
  }

+static void ringbuf_overwrite_mode_subtest(void)
+{
+       unsigned long size, len1, len2, len3, len4, len5;
+       unsigned long expect_avail_data, expect_prod_pos, expect_over_pos;
+       struct test_ringbuf_overwrite_lskel *skel;
+       int err;
+
+       skel = test_ringbuf_overwrite_lskel__open();
+       if (!ASSERT_OK_PTR(skel, "skel_open"))
+               return;
+
+       size = 0x1000;

this will fail on architecture with page size != 4KB, I adjusted this
to use page_size, len1 to page_size / 2 and len2 to page_size / 4

Ah, good catch, thanks for fixing it!

+       len1 = 0x800;
+       len2 = 0x400;
+       len3 = size - len1 - len2 - BPF_RINGBUF_HDR_SZ * 3; /* 0x3e8 */
+       len4 = len3 - 8; /* 0x3e0 */
+       len5 = len3; /* retry with len3 */
+

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