Re: Revised statx(2) man page for review [and AT_EMPTY_PATH question]

From	Al Viro <viro@ZenIV.linux.org.uk>
Newsgroups	linux.kernel
Subject	Re: Revised statx(2) man page for review [and AT_EMPTY_PATH question]
Date	2017-04-26 18:00 +0200
Message-ID	<tAxwe-4hS-13@gated-at.bofh.it> (permalink)
References	<tA6FI-3Yq-19@gated-at.bofh.it> <tAtsB-1D1-11@gated-at.bofh.it>
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On Wed, Apr 26, 2017 at 12:35:08PM +0100, David Howells wrote:

> AT_EMPTY_PATH wasn't there back in 2010.  I could eliminate the:
> 
> 	statx(fd, NULL, 0, ...);
> 
> option in favour of:
> 
> 	statx(fd, "", AT_EMPTY_PATH, ...);
> 
> Any thoughts either way, Al?
> 
> It would seem that AT_EMPTY_PATH should be redundant, though, since you can
> just set the pathname pointer to NULL.

NULL pathname pointer means an error for a lot of existing syscalls, so
if you want to turn them into wrappers for ...at() ones at libc level,
you'd need to do special-casing of NULL both kernel-side and in libc wrappers.

Requiring "" + AT_EMPTY_PATH means a single dereference of userland pointer.  
OTOH, that's not a terrible burden...

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Revised statx(2) man page for review "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2017-04-25 13:20 +0200
  Re: Revised statx(2) man page for review Silvan Jegen <s.jegen@gmail.com> - 2017-04-25 21:00 +0200
    Re: Revised statx(2) man page for review "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2017-04-25 21:50 +0200
  Re: Revised statx(2) man page for review "Dmitry V. Levin" <ldv@altlinux.org> - 2017-04-25 22:10 +0200
    Re: Revised statx(2) man page for review "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2017-04-26 07:50 +0200
      Re: Revised statx(2) man page for review "G. Branden Robinson" <g.branden.robinson@gmail.com> - 2017-04-26 12:50 +0200
  Re: Revised statx(2) man page for review [and AT_EMPTY_PATH question] David Howells <dhowells@redhat.com> - 2017-04-26 13:40 +0200
    Re: Revised statx(2) man page for review [and AT_EMPTY_PATH question] "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2017-04-26 14:20 +0200
      Re: Revised statx(2) man page for review [and AT_EMPTY_PATH question] David Howells <dhowells@redhat.com> - 2017-04-26 17:30 +0200
        Re: Revised statx(2) man page for review [and AT_EMPTY_PATH question] "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2017-04-26 21:10 +0200
    Re: Revised statx(2) man page for review [and AT_EMPTY_PATH question] Al Viro <viro@ZenIV.linux.org.uk> - 2017-04-26 18:00 +0200

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