looks like Linux 6.6...
commit 475d4df82719225510625b4263baa1105665f4b3
Merge: 511fb5bafed1 712143795327
Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Mon Aug 28 11:25:27 2023 -0700
Merge tag 'v6.6-vfs.fchmodat2' of
git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull fchmodat2 system call from Christian Brauner:
"This adds the fchmodat2() system call. It is a revised version of the
fchmodat() system call, adding a missing flag argument. Support for
both AT_SYMLINK_NOFOLLOW and AT_EMPTY_PATH are included.
Adding this system call revision has been a longstanding request but
so far has always fallen through the cracks. While the kernel
implementation of fchmodat() does not have a flag argument the libc
provided POSIX-compliant fchmodat(3) version does. Both glibc and musl
have to implement a workaround in order to support AT_SYMLINK_NOFOLLOW
(see [1] and [2]).
The workaround is brittle because it relies not just on O_PATH and
O_NOFOLLOW semantics and procfs magic links but also on our rather
inconsistent symlink semantics.
This gives userspace a proper fchmodat2() system call that libcs can
use to properly implement fchmodat(3) and allows them to get rid of
their hacks. In this case it will immediately benefit them as the
current workaround is already defunct because of aformentioned
inconsistencies.
In addition to AT_SYMLINK_NOFOLLOW, give userspace the ability to use
AT_EMPTY_PATH with fchmodat2(). This is already possible with
fchownat() so there's no reason to not also support it for
fchmodat2().
The implementation is simple and comes with selftests. Implementation
of the system call and wiring up the system call are done as separate
patches even though they could arguably be one patch. But in case
there are merge conflicts from other system call additions it can be
beneficial to have separate patches"
Link: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/fchmodat.c;h=17eca54051ee28ba1ec3f9aed170a62630959143;hb=a492b1e5ef7ab50c6fdd4e4e9879ea5569ab0a6c#l35
[1]
Link: https://git.musl-libc.org/cgit/musl/tree/src/stat/fchmodat.c?id=718f363bc2067b6487900eddc9180c84e7739f80#n28
[2]
* tag 'v6.6-vfs.fchmodat2' of
git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
selftests: fchmodat2: remove duplicate unneeded defines
fchmodat2: add support for AT_EMPTY_PATH
selftests: Add fchmodat2 selftest
arch: Register fchmodat2, usually as syscall 452
fs: Add fchmodat2()
Non-functional cleanup of a "__user * filename"
On Sun, Aug 25, 2024 at 5:52 AM Alejandro Colomar <alx@xxxxxxxxxx> wrote:
>
> Hi Elliott,
>
> On Fri, Aug 23, 2024 at 02:40:16PM GMT, enh wrote:
> > subject says it all... the "This flag is not currently implemented."
> > on the man page is wrong, i think?
>
> I guess it was right when the text was written in 2006.
>
> $ git blame --follow -- man/man2/chmod.2 | grep currently
> 92f114db82 man2/chmod.2 (Michael Kerrisk 2014-02-21 08:35:27 +0100 207) This flag is not currently implemented.
> $ git blame 92f114db82^ -- man2/fchmodat.2 | grep currently
> a53b8cb2a0 (Michael Kerrisk 2006-05-02 00:05:06 +0000 99) This flag is not currently implemented.
>
> That might perfectly have changed in the last 18 years. :)
>
> Would you mind writing a small program and shell session that
> demonstrates it? It could be interesting for an EXAMPLES section.
>
>
> Have a lovely day!
> Alex
>
> --
> <https://www.alejandro-colomar.es/>
