linux-kernel - Re: [PATCH RFC 0/1] Document how to add a new syscall

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Date:	Tue, 28 Jul 2015 10:41:05 -0600
From:	Shuah Khan <shuahkh@....samsung.com>
To:	David Drysdale <drysdale@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Linux API <linux-api@...r.kernel.org>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	Jonathan Corbet <corbet@....net>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Eric B Munson <emunson@...mai.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Al Viro <viro@...iv.linux.org.uk>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Vivek Goyal <vgoyal@...hat.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	David Herrmann <dh.herrmann@...il.com>,
	Theodore Ts'o <tytso@....edu>,
	Kees Cook <keescook@...omium.org>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Milosz Tanski <milosz@...in.com>, Fam Zheng <famz@...hat.com>,
	Josh Triplett <josh@...htriplett.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-doc@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [PATCH RFC 0/1] Document how to add a new syscall

On 07/28/2015 10:02 AM, David Drysdale wrote:
> On Tue, Jul 28, 2015 at 3:19 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>> On Tue, Jul 28, 2015 at 07:59:16AM -0600, Shuah Khan wrote:
>>> On 07/28/2015 05:41 AM, David Drysdale wrote:
>>>> Given that I've gotten some of the details wrong in the past (and I've
>>>> seen others do likewise), I thought it might be helpful to collate the
>>>> best practices for adding a new system call to the kernel.
>>>>
>>>> Apologies for the wide circulation -- I've tried to include folk who've
>>>> recently added or proposed a system call, as they're most likely to
>>>> have opinions on:
>>>>  - whether this a useful addition to Documentation/
>>>>  - whether the details of the advice are correct and complete.
>>>>
>>>> Shuah, is there anything more that should be added for the Testing
>>>> section in particular?
>>>>
>>>
>>> David,
>>>
>>> Looks good. You could add a one liner on in some cases, it might be
>>> necessary to install headers before test compiles. Other than that,
>>> the information looks good.
>>
>> For perf we still use the syscall() wrapper and we have hardcoded
>> (fallback) syscall numbers in there in case they've not yet reached
>> unistd.h.
>>
>> People update their kernels far more often than their userspace headers.
> 
> How about:
> 
> diff --git a/Documentation/adding-syscalls.txt
> b/Documentation/adding-syscalls.txt
> index 5f52edda8951..b274c3d01edb 100644
> --- a/Documentation/adding-syscalls.txt
> +++ b/Documentation/adding-syscalls.txt
> @@ -389,6 +389,11 @@ reviewers with a demonstration of how user space
> programs will use the system
>  call.  A good way to combine these aims is to include a simple self-test
>  program in a new directory under tools/testing/selftests/.
> 
> +For a new system call, there will obviously be no libc wrapper function and so
> +the test will need to invoke it using syscall(); also, if the system call
> +involves a new userspace-visible structure, the corresponding header will need
> +to be installed to compile the test.
> +

This looks good.

thanks,
-- Shuah


-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@....samsung.com | (970) 217-8978
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