On Monday 02 June 2014 10:12:37 H. Peter Anvin wrote: > On 06/02/2014 08:31 AM, Theodore Ts'o wrote: > > > > I wonder if it would make sense to try to promulgate via the Austin > > group, and possibly the C standards committee the concept of a bit > > pattern (that might commonly be INT_MAX or UINT_MAX) that means "time > > unknown", or "time indefinite" or "we couldn't encode the time". > > > > (time_t)-1 already has this meaning for some calls (e.g. time(2)). > However, this also means Wed Dec 31 23:59:59 UTC 1969, and unfortunately > something similar applies to all possible bit patterns, certainly within > the range of an int. Worse than Wed Dec 31 23:59:59 UTC 1969, on NFSv3 it also means "Sun Feb 7 07:28:15 CET 2106", and that is much harder to distinguish from a real future date. If we had the choice, I'd go for something like 1, i.e. "Thu Jan 1 01:00:01 CET 1970". > > We would then teach gmtime(3) and asctime(3) to print some appropriate > > message, and we could teach programs like find (with the -mtime) > > option, make, tmpwatch, et. al., that they can't make any presumption > > about the comparibility of any timestamp which has a value of > > TIME_UNDEFINIED. > > > > It would be problematic for time(2) or gettimeofday(2) to return > > TIME_UNDEFINED, since there are programs that care about time ticking > > forward, but I could imagine a new interface which would be permitted > > to return a flag indicating that we don't know the current time > > (because the CMOS battery had run down, etc.) so instead we're going > > to be counting the number of seconds since the system was booted. > > This assumes that we actually know that that is the case, which may be > an aggressive assumption. It's harder for time(2), but for the inode case, we can definitely detect when the file system specific representation overflows or underflows, which may be be at a number of very different points of time. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
