Re: [PATCH bpf-next V7 8/8] bpf/selftests: activating bpf_check_mtu BPF-helper

On 11/24/20 6:33 AM, Jesper Dangaard Brouer wrote:

On Fri, 20 Nov 2020 23:41:11 -0800
Andrii Nakryiko [off-list ref] wrote:

quoted

On Fri, Nov 20, 2020 at 8:21 AM Jesper Dangaard Brouer
[off-list ref] wrote:

quoted

Adding selftest for BPF-helper bpf_check_mtu(). Making sure
it can be used from both XDP and TC.

Signed-off-by: Jesper Dangaard Brouer <redacted>
---
  tools/testing/selftests/bpf/prog_tests/check_mtu.c |   37 ++++++++++++++++++++
  tools/testing/selftests/bpf/progs/test_check_mtu.c |   33 ++++++++++++++++++
  2 files changed, 70 insertions(+)
  create mode 100644 tools/testing/selftests/bpf/prog_tests/check_mtu.c
  create mode 100644 tools/testing/selftests/bpf/progs/test_check_mtu.c

diff --git a/tools/testing/selftests/bpf/prog_tests/check_mtu.c b/tools/testing/selftests/bpf/prog_tests/check_mtu.c
new file mode 100644
index 000000000000..09b8f986a17b
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/check_mtu.c

@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Red Hat */
+#include <uapi/linux/bpf.h>
+#include <linux/if_link.h>
+#include <test_progs.h>
+
+#include "test_check_mtu.skel.h"
+#define IFINDEX_LO 1
+
+void test_check_mtu_xdp(struct test_check_mtu *skel)

this should be static func, otherwise it's treated as an independent selftest.

Ok, fixed.

quoted

quoted

+{
+       int err = 0;
+       int fd;
+
+       fd = bpf_program__fd(skel->progs.xdp_use_helper);
+       err = bpf_set_link_xdp_fd(IFINDEX_LO, fd, XDP_FLAGS_SKB_MODE);
+       if (CHECK_FAIL(err))

please use CHECK() or one of ASSERT_xxx() helpers. CHECK_FAIL() should
be used for high-volume unlikely to fail test (i.e., very rarely).

I could not get CHECK() macro working.  I now realize that this is
because I've not defined a global static variable named 'duration'.

  static __u32 duration;

I wonder, are there any best-practice documentation or blogpost on
howto write these bpf-selftests?

The 'duration' in old days is used to measure performance. Today most
of selftests actually do not need this. We do not have doc/blogpost
for this. The best is to look at other files under prog_tests to see
how they handle duration ...

Below signature is the compile error for others to Google for, and
solution above.
-
Best regards,
   Jesper Dangaard Brouer
   MSc.CS, Principal Kernel Engineer at Red Hat
   LinkedIn: http://www.linkedin.com/in/brouer


$ make
   TEST-OBJ [test_progs] check_mtu.test.o
In file included from /home/jbrouer/git/kernel/bpf-next/tools/testing/selftests/bpf/prog_tests/check_mtu.c:6:
/home/jbrouer/git/kernel/bpf-next/tools/testing/selftests/bpf/prog_tests/check_mtu.c: In function ‘test_check_mtu’:
./test_progs.h:129:25: error: ‘duration’ undeclared (first use in this function)
   129 |  _CHECK(condition, tag, duration, format)
       |                         ^~~~~~~~
./test_progs.h:111:25: note: in definition of macro ‘_CHECK’
   111 |          __func__, tag, duration);   \
       |                         ^~~~~~~~
/home/jbrouer/git/kernel/bpf-next/tools/testing/selftests/bpf/prog_tests/check_mtu.c:33:6: note: in expansion of macro ‘CHECK’
    33 |  if (CHECK(!skel, "open and load skel", "failed"))
       |      ^~~~~
./test_progs.h:129:25: note: each undeclared identifier is reported only once for each function it appears in
   129 |  _CHECK(condition, tag, duration, format)
       |                         ^~~~~~~~
./test_progs.h:111:25: note: in definition of macro ‘_CHECK’
   111 |          __func__, tag, duration);   \
       |                         ^~~~~~~~
/home/jbrouer/git/kernel/bpf-next/tools/testing/selftests/bpf/prog_tests/check_mtu.c:33:6: note: in expansion of macro ‘CHECK’
    33 |  if (CHECK(!skel, "open and load skel", "failed"))
       |      ^~~~~
make: *** [Makefile:396: /home/jbrouer/git/kernel/bpf-next/tools/testing/selftests/bpf/check_mtu.test.o] Error 1