Hello,

I have little trouble with the manpage or help output. It mentions:
--mtime=DATE-OR-FILE - does this mean that I can specify a filename
which it would retrieve the reference mtime from (like some other GNU
commands)? What is date, every format that the "date" command accepts?

Let's try:
$ tar c --mtime=0 dbgen/ | tar -t -v
-> looks like 0 was interpreted as 00:00 tonight

On IRC it was mentioned to use @ as prefix to a unix timestamp... ok, it
does the trick and we get the year 1970.

But @ is not documented in the manpage!

Ok, what about a reference file?

$ tar c --mtime=README dbgen/ | tar t -v
tar: Substituting -9223372036854775807 for unknown date format ‘README’
drwxr-xr-x user/user             0 -9223372036854775808 dbgen/
...

That looks utterly wrong. It's either buggy or I just don't know how to
use it and there is no documentation AFAICS.

Regards,
Eduard.