netdev - Re: [PATCH] bpf: fix errno code for unsupported batch ops

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Date:   Mon, 19 Apr 2021 10:52:07 -0300
From:   Pedro Tammela <pctammela@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH] bpf: fix errno code for unsupported batch ops

Em dom., 18 de abr. de 2021 às 19:56, Alexei Starovoitov
<alexei.starovoitov@...il.com> escreveu:
>
> On Sun, Apr 18, 2021 at 1:03 PM Pedro Tammela <pctammela@...il.com> wrote:
> >
> > ENOTSUPP is not a valid userland errno[1], which is annoying for
> > userland applications that implement a fallback to iterative, report
> > errors via 'strerror()' or both.
> >
> > The batched ops return this errno whenever an operation
> > is not implemented for kernels that implement batched ops.
> >
> > In older kernels, pre batched ops, it returns EINVAL as the arguments
> > are not supported in the syscall.
> >
> > [1] https://lore.kernel.org/netdev/20200511165319.2251678-1-kuba@kernel.org/
> >
> > Signed-off-by: Pedro Tammela <pctammela@...atatu.com>
> > ---
> >  kernel/bpf/syscall.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index fd495190115e..88fe19c0aeb1 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -3961,7 +3961,7 @@ static int bpf_task_fd_query(const union bpf_attr *attr,
> >  #define BPF_DO_BATCH(fn)                       \
> >         do {                                    \
> >                 if (!fn) {                      \
> > -                       err = -ENOTSUPP;        \
> > +                       err = -EOPNOTSUPP;      \
>
> $ git grep EOPNOTSUPP kernel/bpf/|wc -l
> 11
> $ git grep ENOTSUPP kernel/bpf/|wc -l
> 51
>
> For new code EOPNOTSUPP is better, but I don't think changing all 51 case
> is a good idea. Something might depend on it already.

OK, makes sense.

Perhaps, handle this errno in 'libbpf_strerror()'? So language
bindings don't get lost when dealing with this errno.