[LEAPSECS] a modest proposal

[Tony Finch]

On Sat, 9 Feb 2008, Steve Allen wrote:

>

> I think that POSIX time_t should be redefined to be TI, with no leap

> seconds.  I think that the leap seconds should be included in the

> zoneinfo files.  POSIX already allows that the local time can be

> offset by an arbitrary number of seconds (not just hours and minutes)

> from the system value of time_t.  The mechanism by which this is

> communicated to POSIX systems is zoneinfo.  The zoneinfo maintainers

> are accustomed to making changes many times a year, with almost no

> advance notice, subject to whims of political entities which are

> much less predictable than leap seconds.

>

> This keeps the simplicity of POSIX system time with the only cost

> being one of interpretation: the system time_t is TI, and UTC be an

> entity derived using zoneinfo.


This is quite an attractive idea. I wonder how to deal with some of the
consequences:

How should the kernel interpret time stamps stored in filesystems? Do you
propose to retrospectively re-interpret them as being in TI instead of
POSIX time? (This is related to the problem that Unixes have with FAT
filesystems that store timestamps in some unspecified local time, which
implies that the kernel can't be ignorant of local time.)

How do you cope with programs that assume that POSIX time is UTC, and
which therefore bypass the tz code when handling UTC timestamps?

How do you represent TI textually? i.e. how should ISO 8601 be revised?

How does this affect NTP, which uses a POSIX-like timescale?

I note that the tz code has had support for your proposal for a very long
time, though it requires compile-time configuration to enable it. (The
tzdata distribution also includes a leapseconds file, though it has not
been updated to bulletin C 35 yet.) Yet no-one ships systems configured
this way.


> This allows all the bureaus of the IERS to continue to represent to

> their funding agencies that their work is essential for the purposes

> of telling the world what time it is.  (If UTC were redefined instead

> of replace with TI, the earth rotation monitoring of the IERS becomes

> moot from the standpoint of commerce.)


Surely its work on the ITRF is still needed for satellite navigation.

Tony.
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