Follow-up for 64f3419ec1.
If the input timestamp is too old (say, 1min since 1970-01-01), then
parse_timestamp() may fail on a timezone with positive shift e.g.
JST (UTC+9). Moreover, even if parse_timestamp() succeeds, its result
'y' and 'usec_sub_unsigned(x, 2 * USEC_PER_DAY)' are both zero, and
the assertion will be triggered.
Fixes#26172.
The documentation on moving an existing homedir into a systemd-homed managed
one suggests using rsync(1) with a bunch of flags to preserve as much metadata
as possible: permissions, xattrs, timestamps, etc. The previously suggested
flags were:
rsync -aHAXv --remove-source-files …
… which does include mtimes, but not ctimes and atimes, because -a does not
include those:
--archive, -a archive mode is -rlptgoD (no -A,-X,-U,-N,-H)
This change adds the -N and -U flags to preserve even more file timestamps,
turning the command into:
rsync -aHANUXv --remove-source-files …
The new flags are:
--crtimes, -N preserve create times (newness)
--atimes, -U preserve access (use) times
This will be used by Tpm2Handle instances, which is added in later patches.
The refcounting allows the context to be retained until all Tpm2Handles have
been cleaned up, and the initial ref is released, before cleaning the context.
