In search of more general enlightenment, can someone (Colin?) explain what the race condition is that's referred to in the manual:
--snaptime file
(c mode only) This option MUST be specified when creating a
backup from a filesystem snapshot, and file must have a modifica-
tion time prior to when the filesystem snapshot was created.
(This is necessary to prevent races between file modification and
snapshot creation which could result in tarsnap failing to recog-
nize that a file has been modified.)
Does this imply that UFS snapshot creation isn't atomic wrt file modification?