linux-kernel - Re: [PATCH v3 1/3] syscalls,x86 Expose arch

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Date:   Fri, 16 Sep 2016 09:50:26 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Kyle Huey <me@...ehuey.com>
cc:     Robert O'Callahan <robert@...llahan.org>,
        linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Borislav Petkov <bp@...e.de>, linux-api@...r.kernel.org,
        xen-devel@...ts.xenproject.org, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Al Viro <viro@...iv.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        Anna Schumaker <Anna.Schumaker@...app.com>,
        Andy Lutomirski <luto@...nel.org>, Zach Brown <zab@...hat.com>,
        Eric B Munson <emunson@...mai.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Jan Beulich <JBeulich@...e.com>,
        Mateusz Guzik <mguzik@...hat.com>,
        Chuck Ebbert <cebbert.lkml@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        "chengang@...ndsoft.com.cn" <chengang@...ndsoft.com.cn>,
        Jeff Moyer <jmoyer@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Milosz Tanski <milosz@...in.com>,
        "open list:USER-MODE LINUX (UML)" 
        <user-mode-linux-devel@...ts.sourceforge.net>,
        "open list:USER-MODE LINUX (UML)" 
        <user-mode-linux-user@...ts.sourceforge.net>
Subject: Re: [PATCH v3 1/3] syscalls,x86 Expose arch_prctl on x86-32.

On Thu, 15 Sep 2016, Kyle Huey wrote:

First of all, please add a cover letter [PATCH 0/N] to your patch series
and send it with something which provides proper mail threading. 
See: git-send-email, quilt 

> arch_prctl is currently 64-bit only. Wire it up for 32-bits, as a no-op for
> now. Rename the second arg to a more generic name.

This changelog is useless.

- it does not provide any rationale for this change, i.e. why this is
  required. Just because its 64bit only is not a reason.

- "Rename the second arg to a more generic name" does not give
  any useful information.

Misleading information is worse than no information.

Further your patch does 5 things at once. It wants to be split into parts:

1) Rename do_arch_prctl() and change the argument name,

> -long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
> +long do_arch_prctl_64(struct task_struct *task, int code, unsigned long arg2)

2) Provide do_arch_prctl_common() and hook it up to the arch_prctl syscall

> -long sys_arch_prctl(int code, unsigned long addr)
> +SYSCALL_DEFINE2(arch_prctl, int, code, unsigned long, arg2)
>  {
> -	return do_arch_prctl(current, code, addr);
> +	long ret;
> +
> +	ret = do_arch_prctl_64(current, code, arg2);
> +	if (ret == -EINVAL)
> +		ret = do_arch_prctl_common(current, code, arg2);
> +
> +	return ret;
>  }

3) Implement the compat version
  
Thanks,

	tflx