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

[Yonghong Song <yhs@fb.com>]

On 11/24/20 6:33 AM, Jesper Dangaard Brouer wrote:
> On Fri, 20 Nov 2020 23:41:11 -0800
> Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
> 
>> On Fri, Nov 20, 2020 at 8:21 AM Jesper Dangaard Brouer
>> <brouer@redhat.com> wrote:
>>>
>>> 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 <brouer@redhat.com>
>>> ---
>>>   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.
> 
>>> +{
>>> +       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
>