When booting the system, truncate the utx.active file, but do write the
BOOT_TIME record into it afterwards. This allows one to obtain the boot
time of the system as follows:
struct utmpx u1 = { .ut_type = BOOT_TIME }, *u2;
setutxent();
u2 = getutxid(&u1);
Now, the boot time is stored in u2->ut_tv, just like on Linux and other
systems.
We don't open the utx.active file with O_EXLOCK. It's rather unlikely
that other applications use this database at the same time and I want to
prevent the possibility of deadlocks in init(8).
Discussed with: pluknet
cb65a7fe02