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

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Message-ID: <c2d6db56-0381-d72c-2c9d-1e0ea324ceff@iogearbox.net>
Date:   Fri, 4 Mar 2022 22:54:54 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     James Hilliard <james.hilliard1@...il.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...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 3/4/22 8:01 PM, Andrii Nakryiko wrote:
> On Mon, Feb 28, 2022 at 7:00 AM Daniel Borkmann <daniel@...earbox.net> wrote:
>> 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)

Sgtm, James, could you respin with using the include?

Thanks,
Daniel