Re: gnulib fsusage

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Date: Thu, 19 Jan 2023 10:24:29 +0800
> 
> Apparently lib/fsusage.o is not built when there is no suitable way for
> it to get the necessary information, but it is still used
> unconditionally by Emacs.

Not unconditionally: the implementation of file-system-info in
fileio.c is conditioned on !DOS_NT, and both MSDOS and WINDOWSNT ports
have their separate implementations which don't use Gnulib's fsusage.

> Is this the right way to detect whether or not get_fs_usage is actually
> present?

Which port needs to exclude it, and why?  Is that port going to
implement its own version of file-system-info?  We must have a
non-trivial working implementation for each supported platform,
because Dired (and Tramp?) uses it.

If the port you are considering will have its own implementation, then
the same method as DOS_NT uses will be appropriate.

> +#else
> +  return Qnil;
> +#endif

I don't think this could fly, because Dired and other places need a
real implementation.  Please tell more about the problem you are
trying to solve.