linux-kernel - Re: [PATCH] sys_waitid: return -EFAULT for NULL

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Date:	Wed, 14 Jan 2009 13:53:10 +1300
From:	"Michael Kerrisk" <mtk.manpages@...glemail.com>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:	"Roland McGrath" <roland@...hat.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"kernel list" <linux-kernel@...r.kernel.org>,
	"Ulrich Drepper" <drepper@...hat.com>,
	"Vegard Nossum" <vegard.nossum@...il.com>,
	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>
Subject: Re: [PATCH] sys_waitid: return -EFAULT for NULL

On Wed, Jan 14, 2009 at 1:33 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
>
> On Tue, 13 Jan 2009, Roland McGrath wrote:
>>
>> It's always been invalid to call waitid() with a NULL pointer.  It was an
>> oversight that it was allowed (and acts like a wait4() call instead).
>
> I'm not going to take this.
>
> If it was some new system call, of if there was some downside to out
> behavior, I might be interested. As it is, our behaviour has zero
> downside, and changing existing interfaces simply isn't worth it.

It has zero downside for *us*.  But it is yet another example of Linux
littering the Unix landscape with unnecessary inconsistencies that
application writers must deal with.  That's a downside for the app
writers.  (But, given how long the existing behavior has been in the
wild, my argument here is somewhat academic...)

> The alleged "downsides" are bogus:
>
>  - POSIX is not that strict.

Well, POSIX.1-2001 is fairly clear:

      The  application shall ensure that the infop argument points to
      a siginfo_t structure.

(Admittedly, this is a requirement imposed on the application, rather
than the implementation, but the standard goes on to say that the
implemenation shall fill in the structure pointed to by infop.)

Cheers,

Michael

>   EFAULT is one of the odd error cases anyway,
>   and even explicit requirements are irrelevant: if somebody wants to get
>   strict conformance paperwork done, you just need to tell where you
>   differ, and you're basically done. But perhaps more important, nobody
>   cares.
>
>  - The "portability" argument is totally bogus, since it's not like you
>   compile programs without even testing to another UNIX _anyway_.
>
> So I'm simply not going to potentially break binaries over something that
> is so _totally_ irrelevant. Document it in the man-page instead.

Well, that's doable of course.

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git
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