Subject: Re: Git should preserve modification times at least on request

From: Theodore Ts'o <[email-masked]>
Date: Mon, 19 Feb 2018 20:22:19 -0500

On Mon, Feb 19, 2018 at 11:08:19PM +0100, Peter Backes wrote:
> Is thetre some existing code that could be used? I think I read 
> somewhere that git once did preserve mtimes, but that this code was 
> removed because of the build tool issues. Perhaps that code could 
> simply be put back in, and surrounded by conditions.

I don't believe that was ever true, because the mod times is simply
not *stored* anywhere.

You might want to consider trying to implement it as hook scripts
first, and see how well/poorly it works for you.  I do have a use
case, which is to maintain the timestamps for guilt (a quilt-like
patch management system which uses git).  At the moment I just use a
manual script, save-timestamps, which looks like this:

#!/bin/sh
stat -c "touch -d @%Y %n" * | sort -k 3 | grep -v "~$" | sort -k3 > timestamps

and then I just include the timestamps file in thhe commit.  When I
unpack the file elsewhere, I just run the command ". timestamps", or
if I am manually editing a single file, I might do:

	grep file-name-of-patch timestamps | sht

This works because the timestamps file has lines which look like
this:

touch -d @1519007593 jbd2-clarify-recovery-checksum-error-msg

I've been too lazy to automate this using a "pre-commit" and
"post-checkout" hook, but it *really* wouldn't be that hard.  Right
now it also only works for files in the top-level of the repo, which
is all I have in my guilt patch repo.  Making this work in a
multiple-directory environment is also left as an exercise to the
reader.  :-)

Cheers,

						- Ted

P.S.  Also left to the reader is making it work on legacy OS's like
Windows.  :-)