Automake's file locking (was Re: Autoconf/Automake is not using version from AC_INIT)

[Zack Weinberg]

On Mon, Jan 25, 2021 at 9:52 AM Bob Friesenhahn
<bfriesen@simple.dallas.tx.us> wrote:
> At the moment it is a big deal for me because the locking prototol
> that Autoconf/Automake is using does not work with NFS mounts for
> Illumos-derived systems when the client is also an Illumos-derived
> system, because Illumos failed to support the legacy locking protocol
> used when the system locking daemon was re-implemented from scratch.
...
> It is likely that a small patch to Automake Perl-based locking code
> could solve this issue by using the same fall-back to using POSIX
> locking rather than legacy locking the same way that GNU/Linux does.
> It may also be that using POSIX locking in the first place is the
> solution.

Automake "just" calls Perl's 'flock' built-in (see 'sub lock' in
Automake/XFile.pm) (this code is copied into Autoconf under the
Autom4te:: namespace).  It would be relatively straightforward to
teach it to try 'fcntl(F_SETLKW, ...)' if that fails.  Do you know
whether that would be sufficient?  If not, we may be up a creek, since
depending on CPAN modules is a non-starter.

zw