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

Michael Kerrisk
2009-01-14T00:53:10Z

On Wed, Jan 14, 2009 at 1:33 PM, Linus Torvalds
<torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.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
man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html