linux-kernel - Re: [PATCH 2/4] m68k: Replace NR_syscalls macro from asm/unistd.h

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Date:   Tue, 18 Sep 2018 12:46:54 +0530
From:   Firoz Khan <firoz.khan@...aro.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Marcin Juszkiewicz <marcin.juszkiewicz@...aro.org>
Subject: Re: [PATCH 2/4] m68k: Replace NR_syscalls macro from asm/unistd.h

On 9 August 2018 at 13:00, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> Hi Firoz,
>
> One first comment below...
>
> On Thu, Aug 9, 2018 at 7:16 AM Firoz Khan <firoz.khan@...aro.org> wrote:
>> NR_syscalls macro holds the number of system call exist in m68k
>> architecture. This macro is currently the part of asm/unistd.h file.
>> We have to change the value of NR_syscalls, if we add or delete a
>> system call.
>>
>> One of patch in this patch series has a script which will generate
>> a uapi header based on syscall.tbl file. The syscall.tbl file
>> contains the number of system call information. So we have two
>> option to update NR_syscalls value.
>>
>> 1. Update NR_syscalls in asm/unistd.h manually by counting the
>>    no.of system calls. No need to update NR_syscalls untill
>>    we either add a new system call or delete an existing system
>>    call.
>>
>> 2. We can keep this feature it above mentioned script, that'll
>>    count the number of syscalls and keep it in a generated file.
>>    In this case we don't need to explicitly update NR_syscalls
>>    in asm/unistd.h file.
>>
>> The 2nd option will be the recommended one. For that, I moved the
>> NR_syscalls macro from asm/unistd.h to uapi/asm/unistd.h. The macro
>> name also changed form NR_syscalls to __NR_syscalls for making the
>> name convention same across all architecture. While __NR_syscalls
>> isn't strictly part of the uapi, having it as part of the generated
>> header to simplifies the implementation.
>
> It can indeed not be part of the UAPI, as UAPI definitions can never change,
> while new syscalls will be added in the future, increasing the number ;-)

Thanks for your reply :)
Sorry for the delayed response :(

I would like to keep __NR_syscalls macro to uapi header in order to simplify
the system call table generation script. Otherwise the __NR_syscalls
macro need to update manually. That become a problem.

Please check the below implementation in uapi file make sense?
It is an easy workaround to leave __NR_syscalls macro in uapi/asm/unistd.h
and enclose it in #ifdef __KERNEL__

...
...
#define __NR_pwritev2  378
#define __NR_statx      379

#ifdef __KERNEL__
#define __NR_syscalls   380
#endif
...
...

>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds