On 2026-06-29 01:35, Liu Chao via tz wrote:
I was working along the same idea as you, and installed the attached
slightly-bigger patch; please give it a try.
It works, thanks.
Thanks for checking; glad to hear that things work now.
By the way, what do you need rearguard for? Is this for Java, or
something else?
One reason is for Java. At the same time, it is also to keep the same as other
OS vendors (such as RHEL). If switching from rearguard to vanguard now, it
might affect upper-layer third-party softwares and require a significant amount
of time to explain the differences between these changes.
Yes, and Java is the primary reason we still have rearguard format.
Eventually I'd like to delegate the maintenance of rearguard format to
the Java folks (assuming they still need it then) as it is a pain to
maintain (as witness our emails in this thread!) and they're the only
ones I know who still need it - which is why I asked about Java.
As I understand it, although older versions of RHEL used rearguard
format, the current version (RHEL 10) uses the main format. So
eventually RHEL's need for the old format should go away.
For example, the glibc contains a global variable timezone, which is the
opposite value of the gmtoff value in the last line of the timezone with
isdst=0. In some time zones, the values of timezone in rearguard and vanguard
modes are different.
Yes, just as tm_isdst differs. That's fine, and is expected.
I have seen some softwares directly add or subtract the timezone value to
convert the local time to the UTC time.
Any such software is broken, because 'timezone' is the difference
between local time and UT during only part of the year, and this is true
regardless of whether rearguard format is used. So this issue shouldn't
lead to a preference for rearguard format - unless the goal is to
reproduce old bugs.
Anyway, as you probably know, 'timezone' does not suffice for proper
timekeeping, which is why 'timezone' is planned to be removed in a
future version of POSIX. See
<https://data.iana.org/time-zones/theory.html#functions> and look for
"POSIX features no longer needed". So any problem with rearguard and
'timezone' will go away eventually.
