netdev - Re: [PATCH v5 bpf-next 3/4] bpf: Add kernel module with user mode driver that populates bpffs.

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Date:   Mon, 3 Aug 2020 10:51:46 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v5 bpf-next 3/4] bpf: Add kernel module with user mode
 driver that populates bpffs.

On Mon, Aug 3, 2020 at 10:41 AM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> On 8/3/20 7:34 PM, Daniel Borkmann wrote:
> > On 8/3/20 7:15 PM, Daniel Borkmann wrote:
> >> On 8/3/20 12:29 AM, Alexei Starovoitov wrote:
> >>> From: Alexei Starovoitov <ast@...nel.org>
> >>>
> >>> Add kernel module with user mode driver that populates bpffs with
> >>> BPF iterators.
> >>>

[...]

>    CC      kernel/events/ring_buffer.o
>    CC [U]  kernel/bpf/preload/./../../../tools/lib/bpf/bpf.o
>    CC [U]  kernel/bpf/preload/./../../../tools/lib/bpf/libbpf.o
> In file included from kernel/bpf/preload/./../../../tools/lib/bpf/libbpf.c:47:0:
> ./tools/include/tools/libc_compat.h:11:21: error: static declaration of ‘reallocarray’ follows non-static declaration
>   static inline void *reallocarray(void *ptr, size_t nmemb, size_t size)
>                       ^~~~~~~~~~~~
> In file included from kernel/bpf/preload/./../../../tools/lib/bpf/libbpf.c:16:0:
> /usr/include/stdlib.h:558:14: note: previous declaration of ‘reallocarray’ was here
>   extern void *reallocarray (void *__ptr, size_t __nmemb, size_t __size)
>                ^~~~~~~~~~~~

A bit offtopic. reallocarray and related feature detection causes so
much hassle, that I'm strongly tempted to just get rid of it in the
entire libbpf. Or just unconditionally implement libbpf-specific
reallocarray function. Any objections?

>    CC      kernel/user-return-notifier.o
> scripts/Makefile.userprogs:43: recipe for target 'kernel/bpf/preload/./../../../tools/lib/bpf/libbpf.o' failed
> make[3]: *** [kernel/bpf/preload/./../../../tools/lib/bpf/libbpf.o] Error 1
> scripts/Makefile.build:497: recipe for target 'kernel/bpf/preload' failed
> make[2]: *** [kernel/bpf/preload] Error 2
> scripts/Makefile.build:497: recipe for target 'kernel/bpf' failed
> make[1]: *** [kernel/bpf] Error 2
> make[1]: *** Waiting for unfinished jobs....
> [...]