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

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Message-ID: <6af1530a-a4bf-dccf-947d-78ce235a4414@iogearbox.net>
Date:   Mon, 28 Feb 2022 16:00:00 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     James Hilliard <james.hilliard1@...il.com>, bpf@...r.kernel.org
Cc:     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>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] libbpf: ensure F_DUPFD_CLOEXEC is defined

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)?

> ---
>   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