linux-kernel - Extending syscalls (was: [PATCH 1/2] Extend sys_clone and sys

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Message-ID: <25712.1200582125@vena.lwn.net>
Date:	Thu, 17 Jan 2008 08:02:05 -0700
From:	corbet@....net (Jonathan Corbet)
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Pavel Emelyanov <xemul@...nvz.org>,
	Linux Containers <containers@...ts.osdl.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Cedric Le Goater <clg@...ibm.com>, drepper@...hat.com,
	Serge Hallyn <serue@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Extending syscalls (was: [PATCH 1/2] Extend sys_clone and sys_unshare system calls API)

Al Viro sez:

> Nah, just put an XML parser into the kernel to have the form match the
> contents...
> 
> Al "perhaps we should newgroup alt.tasteless.api for all that stuff" Viro

Heh, indeed.  But we do seem to have a recurring problem of people
wanting to extend sys_foo() beyond the confines of its original API.
I've observed a few ways of doing that:

 - create sys_foo2() (or sys_foo64(), or sys_fooat(), or sys_pfoo(),
   or...) and add the new stuff there.

 - Put a version number into the API somewhere - wireless extensions,
   for example.

 - Set a flag saying "I've stashed some additional parameters somewhere
   else."  That's sys_indirect() and the current proposal for extending
   clone().

 - Just do it all with a kernel-based XML parser.  I think we should
   call this approach sys_viro() in honor of its champion.

 - Do it all in sysfs

The first approach has traditionally been the most popular.  If we have
a consensus that this is the way to extend system calls in the future,
it would be nice to set that down somewhere.  We could avoid a lot of
API blind alleys that way.

jon
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