netdev - Re: [PATCH bpf v1 2/3] selftests/bpf: Print a message when tester could not run a program

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Date:   Thu, 16 May 2019 18:21:32 +0200
From:   Krzesimir Nowak <krzesimir@...volk.io>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     bpf@...r.kernel.org,
        Iago López Galeiras <iago@...volk.io>,
        "Alban Crequy (Kinvolk)" <alban@...volk.io>,
        Shuah Khan <shuah@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrey Ignatov <rdna@...com>, linux-kselftest@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf v1 2/3] selftests/bpf: Print a message when tester
 could not run a program

On Thu, May 16, 2019 at 5:51 PM Jakub Kicinski
<jakub.kicinski@...ronome.com> wrote:
>
> On Thu, 16 May 2019 11:29:39 +0200, Krzesimir Nowak wrote:
> > > > diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> > > > index ccd896b98cac..bf0da03f593b 100644
> > > > --- a/tools/testing/selftests/bpf/test_verifier.c
> > > > +++ b/tools/testing/selftests/bpf/test_verifier.c
> > > > @@ -825,11 +825,20 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
> > > >                               tmp, &size_tmp, &retval, NULL);
> > > >       if (unpriv)
> > > >               set_admin(false);
> > > > -     if (err && errno != 524/*ENOTSUPP*/ && errno != EPERM) {
> > > > -             printf("Unexpected bpf_prog_test_run error ");
> > > > -             return err;
> > > > +     if (err) {
> > > > +             switch (errno) {
> > > > +             case 524/*ENOTSUPP*/:
> > > > +                     printf("Did not run the program (not supported) ");
> > > > +                     return 0;
> > > > +             case EPERM:
> > > > +                     printf("Did not run the program (no permission) ");
> > > > +                     return 0;
> > >
> > > Perhaps use strerror(errno)?
> >
> > As I said in the commit message, I open-coded those messages because
> > strerror for ENOTSUPP returns "Unknown error 524".
>
> Ah, sorry, missed that.  I wonder if that's something worth addressing
> in libc, since the BPF subsystem uses ENOTSUPP a lot.

The "not supported" errno situation seems to be a mess. There is an
ENOTSUP define in libc. ENOTSUP is usually defined to be EOPNOTSUPP
(taken from kernel), which in turn seems to have a different value
(95) than kernel's ENOTSUPP (524). Adding ENOTSUPP (with two Ps) to
libc would only add to the confusion. So it's kind of meh and I guess
people just moved on with workarounds.

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