Re: preserve timestamps when installing headers

Michael Paquier <michael(at)paquier(dot)xyz> writes:
> On Tue, Oct 12, 2021 at 01:22:50PM +0300, Alexander Kuzmenkov wrote:
>> This patch adds `-p` switch to `cp` invocation in
>> these files, to make it preserve timestamps.

> The use of cp instead of $(INSTALL_DATA) for the installation of the
> headers comes from a703269, back from 2005. How do numbers compare
> today, 16 years later?

According to a nearby copy of POSIX, "cp -p" does a lot more than
preserve timestamps. It also specifies preserving file ownership,
which seems absolutely catastrophic for the standard use-case of
"build as some ordinary user, then install as root".

TBH, I am not convinced that the complained-of case is enough of a
problem to justify any change in our build rules, even if there
weren't any semantic issues. If you are worried about build times,
you should be using ccache, and IME builds using ccache are not
terribly impacted by file timestamp changes.

regards, tom lane