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

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

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

...

From: Xu Kuohai xukuohai@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 xukuohai@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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