netdev - Re: [PATCH 1/1] libbpf: ensure F_DUPFD

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Message-ID: <CAEf4Bza84V1hwknb9XR+cNz8Sy4BK2EMYB-Oudq==pOYpqV0nw@mail.gmail.com>
Date:   Fri, 4 Mar 2022 11:01:26 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     James Hilliard <james.hilliard1@...il.com>,
        bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        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>,
        Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] libbpf: ensure F_DUPFD_CLOEXEC is defined

On Mon, Feb 28, 2022 at 7:00 AM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> Hi James,
>
> On 2/27/22 3:25 PM, James Hilliard wrote:
> > This definition seems to be missing from some older toolchains.
> >
> > Note that the fcntl.h in libbpf_internal.h is not a kernel header
> > but rather a toolchain libc header.
> >
> > Fixes:
> > libbpf_internal.h:521:18: error: 'F_DUPFD_CLOEXEC' undeclared (first use in this function); did you mean 'FD_CLOEXEC'?
> >     fd = fcntl(fd, F_DUPFD_CLOEXEC, 3);
> >                    ^~~~~~~~~~~~~~~
> >                    FD_CLOEXEC
> >
> > Signed-off-by: James Hilliard <james.hilliard1@...il.com>
>
> Do you have some more info on your env (e.g. libc)? Looks like F_DUPFD_CLOEXEC
> was added back in 2.6.24 kernel. When did libc add it?

It seems like it's guarded by __USE_XOPEN2K8 in glibc (from a quick
glance at glibc code). But it's been there since 2010 or so, at the
very least.

>
> Should we instead just add an include for <linux/fcntl.h> to libbpf_internal.h
> (given it defines F_DUPFD_CLOEXEC as well)?

yep, this is UAPI header so we can use it easily (we'll need to sync
it into Github repo, but that's not a problem)


>
> > ---
> >   tools/lib/bpf/libbpf_internal.h | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> > index 4fda8bdf0a0d..d2a86b5a457a 100644
> > --- a/tools/lib/bpf/libbpf_internal.h
> > +++ b/tools/lib/bpf/libbpf_internal.h
> > @@ -31,6 +31,10 @@
> >   #define EM_BPF 247
> >   #endif
> >
> > +#ifndef F_DUPFD_CLOEXEC
> > +#define F_DUPFD_CLOEXEC 1030
> > +#endif
> > +
> >   #ifndef R_BPF_64_64
> >   #define R_BPF_64_64 1
> >   #endif
> >
>
> Thanks,
> Daniel