linux-kernel - Re: [PATCHv2 1/1] Documentation: describe how to add a system call

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Message-ID: <20150731220828.GA30890@cloud>
Date:	Fri, 31 Jul 2015 15:08:28 -0700
From:	josh@...htriplett.org
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Kees Cook <keescook@...omium.org>,
	David Drysdale <drysdale@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Linux API <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>,
	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>,
	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>,
	Milosz Tanski <milosz@...in.com>, Fam Zheng <famz@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCHv2 1/1] Documentation: describe how to add a system call

On Fri, Jul 31, 2015 at 02:19:29PM -0700, Andy Lutomirski wrote:
> On Fri, Jul 31, 2015 at 1:59 PM,  <josh@...htriplett.org> wrote:
> > Agreed.  I think the proposal above would be a net improvement, but
> > ideally you'd want something that's annotated and generates automatic
> > marshalling code.
> >
> 
> I assume this is idle musing.  If, however, we were to actually do
> this, I'd suggest we seriously consider speaking the Cap'n Proto
> serialization format.  It's quite nice, it encodes and decodes *very*
> quickly and, unlike TLV schemes, you don't have to read it in order,
> making the read-side code less awkward.

That seems like *massive* overkill for a kernel<->userspace syscall
interface.  I was more thinking about having a few standardized marshal
types, and incrementally adding more when more patterns show up.  For a
first pass, just automatically running copy_from_user and
copy_param_struct on appropriate sets of __user parameters identified as
such in a structured text file seems quite sufficient.  (Plus
automatically generating syscalls.h from that.)
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