[systemd-devel] hwclock

[Tom Gundersen]

Hi guys,

Further to my previous mail about hwclock, I'm struggling to get my
head around what is the "proper" way to handle hwclock's adjfile.

These are my assumptions:

/etc is in principle mounted read-only (not yet possible, but that's
the goal, right?)
/var is in principle not available during early boot
the drift of the hardware clock is updated at regular intervals and
cannot be on a read-only filesystem (but it is ok that we don't know
the drift at early boot (is this true?))
we need to know whether or not the hardware clock is in utc during
early boot (is this actually required? if not, could someone point me
to a discussion/documentation?)

If all of this is correct, it seems to me that the only solution
(without changing hwclock) is to ignore the utc/localtime part of
adjfile and have a config file in /etc that stores whether or not we
use utc (resp., localtime) and always invoke hwclock with
"--adjfile=/var/hwclock/adjfile --utc" (resp.,
"--adjfile=/var/hwclock/adjfile --localtime").

I realise that if someone oblivious to this policy were to call
hwclock without --adjfile, havoc would ensue, but this is the best I
could come up with.

I'd be happy to prepare a patch, if someone can confirm that my
approach is sound.

Cheers,

Tom