linux-kernel - Re: [PATCHv3 1/1] Documentation: describe how to add a system call

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Date:	Wed, 5 Aug 2015 18:21:31 +0200
From:	Pavel Machek <pavel@....cz>
To:	David Drysdale <drysdale@...gle.com>
Cc:	linux-api@...r.kernel.org,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	Shuah Khan <shuahkh@....samsung.com>,
	Jonathan Corbet <corbet@....net>,
	Eric B Munson <emunson@...mai.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Cyril Hrubis <chrubis@...e.cz>,
	Josh Triplett <josh@...htriplett.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	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>,
	Peter Zijlstra <peterz@...radead.org>,
	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>,
	Milosz Tanski <milosz@...in.com>, Fam Zheng <famz@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 1/1] Documentation: describe how to add a system call

Hi!

> Add a document describing the process of adding a new system call,
> including the need for a flags argument for future compatibility, and
> covering 32-bit/64-bit concerns (albeit in an x86-centric way).
> 
> Signed-off-by: David Drysdale <drysdale@...gle.com>
> Reviewed-by: Michael Kerrisk <mtk.manpages@...il.com>
> Reviewed-by: Eric B Munson <emunson@...mai.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Reviewed-by: Randy Dunlap <rdunlap@...radead.org>
> ---
>  Documentation/adding-syscalls.txt | 531 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 531 insertions(+)
>  create mode 100644 Documentation/adding-syscalls.txt

We usually align documentation to less than 80 columns, afaict.

> +call.  To make sure that userspace programs can safely use flags between kernel
> +versions, check whether the flags value holds any unknown flags, and reject the
> +sycall (with EINVAL) if it does:

syscall?

> +New system call proposals, like any change to the kernel's API, should always
> +be cc'ed to linux-api@...r.kernel.org

. at and of sentence?

> +System Calls Returning Elsewhere
> +--------------------------------
> +
> +For most system calls, once the system call is complete the user program
> +continues exactly where it left off -- at the next instruction, with the same
> +stack and registers as before the system call, and with the same virtual
> +memory space.

Umm. Normally we place return value in register. And I'm not sure.. do
syscalls preserve registers that are normally caller-clobbered in the ABI?

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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