linux-kernel - Re: [PATCH 1/3] microblaze: Replace NR

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Date:   Tue, 18 Sep 2018 12:07:01 +0530
From:   Firoz Khan <firoz.khan@...aro.org>
To:     Michal Simek <michal.simek@...inx.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        y2038@...ts.linaro.org, linux-kernel@...r.kernel.org,
        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 1/3] microblaze: Replace NR_syscalls macro from asm/unistd.h

On 9 August 2018 at 12:18, Michal Simek <michal.simek@...inx.com> wrote:
> On 9.8.2018 07:27, Firoz Khan wrote:
>> __NR_syscalls macro holds the number of system call exist in this
>> architecture. This macro is currently the part of asm/unistd.h file.
>> We have change the value of __NR_syscalls, if we add or delete a
>> system call.
>>
>> One of the 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.
>
> This macro was in unistd.h in past but it was moved out because it was
> causing problem with strace.
>
> commit 40c2702a02b755e0183b702778331b351f3be20c
> Author:     Michal Simek <michal.simek@...inx.com>
> AuthorDate: Mon Jul 8 09:50:24 2013 +0200
> Commit:     Michal Simek <michal.simek@...inx.com>
> CommitDate: Wed Jul 10 07:32:09 2013 +0200
>
>     microblaze: Move __NR_syscalls from uapi
>
>
> That's why I don't think this is the right thing to do.
> I have grepped strace and glibc and none is using this macro that's why
> I think it shouldn't be exported via uapi.


Thanks for you 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_pkey_free  397
#define __NR_statx      398

#ifdef __KERNEL__
#define __NR_syscalls   399
#endif
...
...

- Firoz