netdev - Re: [PATCH 2/2] selftests/bpf: Avoid errno clobbering

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Date:   Thu, 3 Dec 2020 13:13:29 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Florian Lehner <dev@...-flo.net>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        john fastabend <john.fastabend@...il.com>,
        Krzesimir Nowak <krzesimir@...volk.io>
Subject: Re: [PATCH 2/2] selftests/bpf: Avoid errno clobbering

On Wed, Dec 2, 2020 at 11:46 AM Florian Lehner <dev@...-flo.net> wrote:
>
> Print a message when the returned error is about a program type being
> not supported or because of permission problems.
> These messages are expected if the program to test was actually
> executed.
>
> Cc: Krzesimir Nowak <krzesimir@...volk.io>
> Signed-off-by: Florian Lehner <dev@...-flo.net>
> ---
>  tools/testing/selftests/bpf/test_verifier.c | 26 +++++++++++++++++----
>  1 file changed, 21 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> index ceea9409639e..86ef28dd9919 100644
> --- a/tools/testing/selftests/bpf/test_verifier.c
> +++ b/tools/testing/selftests/bpf/test_verifier.c
> @@ -875,19 +875,35 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
>         __u8 tmp[TEST_DATA_LEN << 2];
>         __u32 size_tmp = sizeof(tmp);
>         uint32_t retval;
> -       int err;
> +       int err, saved_errno;
>
>         if (unpriv)
>                 set_admin(true);
>         err = bpf_prog_test_run(fd_prog, 1, data, size_data,
>                                 tmp, &size_tmp, &retval, NULL);
> +       saved_errno = errno;
> +
>         if (unpriv)
>                 set_admin(false);
> -       if (err && errno != 524/*ENOTSUPP*/ && errno != EPERM) {
> -               printf("Unexpected bpf_prog_test_run error ");
> -               return err;
> +
> +       if (err) {
> +               switch (saved_errno) {
> +               case 524/*ENOTSUPP*/:
> +                       printf("Did not run the program (not supported) ");
> +                       return 0;
> +               case EPERM:
> +                       if (unpriv) {
> +                               printf("Did not run the program (no permission) ");
> +                               return 0;
> +                       }

I see people specifying /* fallthrough; */ to make explicit that we
expect falling through into default case?

> +               default:
> +                       printf("FAIL: Unexpected bpf_prog_test_run error (%s) ",
> +                               strerror(saved_errno));
> +                       return err;
> +               }
>         }
> -       if (!err && retval != expected_val &&
> +
> +       if (retval != expected_val &&
>             expected_val != POINTER_VALUE) {
>                 printf("FAIL retval %d != %d ", retval, expected_val);
>                 return 1;
> --
> 2.28.0
>