bug#64937: "who" reports funny dates

[Bruno Haible]

Paul Eggert wrote:
> Thanks for doing all that work. I looked into it, and found a problem: a 
> command like "who /var/log/wtmp" stops working because the systemd 
> emulation of read_utmp only supports plain "who" (roughly equivalent to 
> "who /var/run/utmp" on Fedora).

Probably the FILE argument to 'who' and to 'users' should be deprecated?
Since in systemd mode, the only supported value for FILE is /var/run/utmp.

> Although I toyed with the idea of simplifying readutmp.h 
> further, by moving most of it into readutmp.c and having just struct 
> gl_utmp public (this would simplify coreutils quite a bit), I ran out of 
> time and patience and decided to ship what I had.

Yes, I see how much contortions (strncpy etc.) these not-NUL-terminated
strings cause. And two separate code paths, one for the systemd mode and
one for all other platforms, is not ideal from the code coverage/testing/QA
perspective either.

I didn't tackle this, because before the add_utmp function existed, it
would have caused many extra malloc() calls on all platforms.

Bruno