Re: [PATCH] meson: wire up USE_NSEC build knob

[Jeff King <peff@peff.net>]

On Mon, Jun 29, 2026 at 08:08:42AM +0200, Patrick Steinhardt wrote:

> > True, but AFAICT it probably is safe these days, at least one some
> > platforms.
> 
> Hm. That makes me wonder whether it is the completely wrong approach to
> make this a build option then. If it works on some systems and only on
> some filesystems, then a build option is just too coarse-grained. A
> distro wouldn't really be able to ever enable the option, unless it knew
> that repositories will only ever exist on a filesystem that works. Which
> I guess is an assumption that no distro can make.
> 
> So instead, I wonder whether we should treat this the same as for
> example "core.ignoreCase", where we only use nanosecond resolution when
> opted in by the user. Ideally, if we had a way to detect brokenness, we
> could even make git-init(1) set it automatically.

Yeah, this came up earlier in the thread. It would be nice if we could
set it automatically, but I'm not sure we have a good way of testing a
particular filesystem. I think the sequence is:

  1. stat() a file, getting nanoseconds

  2. somehow flush the kernel's in-core inode cache

  3. stat() it again and compare

Step 2 is the tricky part. ;) It's not only not portable, but probably
something that would annoy users if we did it for every repo creation.

It would also be nice if we could actually verify that the sequence
above _does_ show the problem. I was not able to come up with a failing
instance on my modern Linux machine (even going as far as unmounting and
re-mounting for step 2).

But I do agree in general that it should be a config flag and not a
build option. Run-time flags are more friendly to users when there is no
good reason to avoid them.

-Peff