linux-kernel - Re: [PATCH 1/1] libbpf: ensure F_DUPFD

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Date:   Mon, 7 Mar 2022 17:35:19 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     James Hilliard <james.hilliard1@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>, 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>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] libbpf: ensure F_DUPFD_CLOEXEC is defined

On Sat, Mar 5, 2022 at 1:54 AM James Hilliard <james.hilliard1@...il.com> wrote:
>
> On Mon, Feb 28, 2022 at 8:00 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?
> >
> > Should we instead just add an include for <linux/fcntl.h> to libbpf_internal.h
> > (given it defines F_DUPFD_CLOEXEC as well)?
>
> That seems to cause a conflict: error: redefinition of ‘struct flock’
>
>
> >
> > > ---
> > >   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

Let's just do this then (assuming the value of F_DUPFD_CLOEXEC is
architecture-independent)

> > > +
> > >   #ifndef R_BPF_64_64
> > >   #define R_BPF_64_64 1
> > >   #endif
> > >
> >
> > Thanks,
> > Daniel