Re: futimens use of utimensat does not support O_PATH fds

[Josh Triplett <josh@joshtriplett.org>]

On Fri, Aug 08, 2025 at 03:22:58PM +0200, Christian Brauner wrote:
> On Thu, Aug 07, 2025 at 02:01:15PM -0700, Josh Triplett wrote:
> > I just discovered that opening a file with O_PATH gives an fd that works
> > with
> > 
> > utimensat(fd, "", times, O_EMPTY_PATH)
> > 
> > but does *not* work with what futimens calls, which is:
> > 
> > utimensat(fd, NULL, times, 0)
> 
> It's in line with what we do for fchownat() and fchmodat2() iirc.
> O_PATH as today is a broken concept imho. O_PATH file descriptors
> should've never have gained the ability to meaningfully alter state. I
> think it's broken that they can be used to change ownership or mode and
> similar.

In the absence of having O_PATH file descriptors, what would be the way
to modify the properties of a symlink using race-free
file-descriptor-based calls rather than filenames? AFAICT, there's no
way to get a file descriptor corresponding to a symbolic link without
using `O_PATH | O_NOFOLLOW`.

It makes sense that a file descriptor for a symbolic link would be able
to do inode operations but not file operations.