June 2020 - tz - lists.iana.org

North Vietnam 1970 to 1970 - Asia/Hanoi belongs into main file
by Alois Treindl June 28, 2020

June 28, 2020

The backzone file contains the zone Asia/Hanoi It should go into the main file for Asia. There exists no doubt that in all of what was North Vietnam between at least 1970 and 1975 the timezone was 7h east, and not 8h east as in South Vietnam. There may be unclear borders, but most of North Vietnam, including its capital, was not unclear at all. I find it a discrimination of former North Vietnam to not have it represented correctly, at least for the post-1970 period. What Paul Eggert writes in the comments is a poor excuse. From Paul Eggert (2019-02-19): # # The Ho Chi Minh entry suffices for most purposes as it agrees with all of # Vietnam since 1975-06-13. Presumably clocks often changed in south Vietnam # in the early 1970s as locations changed hands during the war; however the # details are unknown and would likely be too voluminous for this database. # # For timestamps in north Vietnam back to 1970 (the tzdb cutoff), # use Asia/Bangkok; see the VN entries in the file zone1970.tab. # For timestamps before 1970, see Asia/Hanoi in the file 'backzone'.

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Use or Apply for SPDX Licence
by Brian Inglis June 23, 2020

June 23, 2020

Hi folks, It would be useful to distributions, packagers, and organization licence checkers if the tzcode and tzdata were covered by (a) Public Domain SPDX licence identifier(s) https://spdx.org/licenses/ e.g. CC-PDDC, PDDL, SAX-PD, Unlicense, WTFPL, etc. or applied for it's own e.g. IANA-TZ-PD. -- Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada This email may be disturbing to some readers as it contains too much technical detail. Reader discretion is advised. [Data in IEC units and prefixes, physical quantities in SI.]

10 14

[PROPOSED] zic now defaults to ‘-b slim’
by Paul Eggert June 21, 2020

June 21, 2020

Make zic’s ‘-b slim’ option the default. This option first appeared in tzdb 2019b (2019-07-01), and is already the default in NetBSD 9.0 (2020-02-14) and seems to be working there. Using slim format should help finish off the TZif format’s Y2038 transition that began in tzcode 95f (1995-10-28). * Makefile, NEWS, zic.8: Mention this. * zic.c (ZIC_BLOAT_DEFAULT): Default to "slim". --- Makefile | 10 +++++----- NEWS | 2 ++ zic.8 | 10 ++++------ zic.c | 5 ++--- 4 files changed, 13 insertions(+), 14 deletions(-) diff --git a/Makefile b/Makefile index 0da7c3f..8abd4d0 100644 --- a/Makefile +++ b/Makefile @@ -22,6 +22,7 @@ BUGEMAIL= tz(a)iana.org # DATAFORM= main # To wait even longer for new features, use: # DATAFORM= rearguard +# Rearguard users might also want "ZFLAGS = -b fat"; see below. DATAFORM= main # Change the line below for your timezone (after finding the one you want in @@ -249,13 +250,12 @@ LDLIBS= # other than simply getting garbage data # -DUSE_LTZ=0 to build zdump with the system time zone library # Also set TZDOBJS=zdump.o and CHECK_TIME_T_ALTERNATIVES= below. -# -DZIC_BLOAT_DEFAULT=\"slim\" to default zic's -b option to "slim", and -# similarly for "fat". Fat TZif files work around incompatibilities +# -DZIC_BLOAT_DEFAULT=\"fat\" to default zic's -b option to "fat", and +# similarly for "slim". Fat TZif files work around incompatibilities # and bugs in some TZif readers, notably readers that mishandle 64-bit # data in TZif files. Slim TZif files are more efficient and do not # work around these incompatibilities and bugs. If not given, the -# current default is "fat" but this is intended to change as readers -# requiring fat files often mishandle timestamps after 2037 anyway. +# default is "slim". # -DZIC_MAX_ABBR_LEN_WO_WARN=3 # (or some other number) to set the maximum time zone abbreviation length # that zic will accept without a warning (the default is 6) @@ -390,7 +390,7 @@ ZIC= $(zic) $(ZFLAGS) # To shrink the size of installed TZif files, # append "-r @N" to omit data before N-seconds-after-the-Epoch. -# You can also append "-b slim" if that is not already the default; +# To grow the files and work around older application bugs, append "-b fat"; # see ZIC_BLOAT_DEFAULT above. # See the zic man page for more about -b and -r. ZFLAGS= diff --git a/NEWS b/NEWS index bfe02ea..6b9fd43 100644 --- a/NEWS +++ b/NEWS @@ -23,6 +23,8 @@ Unreleased, experimental changes Changes to code + zic now defaults to '-b slim' instead of to '-b fat'. + zic's new '-l -' and '-p -' options uninstall any existing localtime and posixrules files, respectively. diff --git a/zic.8 b/zic.8 index a431311..8d34368 100644 --- a/zic.8 +++ b/zic.8 @@ -61,15 +61,13 @@ is .BR slim , keep the output files small; this can help check for the bugs and incompatibilities. -Although the default is currently -.BR fat , -this is intended to change in future -.B zic -versions, as software that mishandles the 64-bit data typically +The default is +.BR slim , +as software that mishandles 64-bit data typically mishandles timestamps after the year 2038 anyway. Also see the .B \*-r -option for another way to shrink output size. +option for another way to alter output size. .TP .BI "\*-d " directory Create time conversion information files in the named directory rather than diff --git a/zic.c b/zic.c index c874b04..3aed819 100644 --- a/zic.c +++ b/zic.c @@ -661,8 +661,7 @@ static const char * tzdefault; static const char * yitcommand; /* -1 if the TZif output file should be slim, 0 if default, 1 if the - output should be fat for backward compatibility. Currently the - default is fat, although this may change. */ + output should be fat for backward compatibility. The default is slim. */ static int bloat; static bool @@ -672,7 +671,7 @@ want_bloat(void) } #ifndef ZIC_BLOAT_DEFAULT -# define ZIC_BLOAT_DEFAULT "fat" +# define ZIC_BLOAT_DEFAULT "slim" #endif int -- 2.17.1

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Sudan/Khartoum time zone
by Ubay Abdelgadir June 21, 2020

June 21, 2020

Dears at IANA, Khartoum's time zone is +2 since 1/Nov/2017. I think it is wrong in the IANA database: Zone Africa/Khartoum 2:10:08 - LMT 1931 2:00 Sudan CA%sT 2000 Jan 15 12:00 3:00 - EAT 2017 Nov 1 2:00 - CAT BR Ubay Abdelgadir

3 2

Formal models and the need for storing original source data
by Michael Kenniston June 21, 2020

June 21, 2020

> > ---------- Forwarded message ---------- > From: Robert Elz <kre(a)munnari.oz.au> > To: Lester Caine <lester(a)lsces.uk> > Cc: tz(a)iana.org > Bcc: > Date: Wed, 03 Jun 2020 19:31:43 +0700 > Subject: Re: [tz] How good is pre-1970 time zone history represented in TZ > database? > Date: Wed, 3 Jun 2020 12:22:32 +0100 > From: Lester Caine <lester(a)lsces.uk> > Message-ID: <3576438c-e0bd-7188-2153-43d80e9054b8(a)lsces.uk> > > There are two kinds of > changes that may be made to a zone. One affects only future timestamps, > and is the common old garden variety "government interference" or however > you think of it. These are far and away the most common changes. While > when we have insufficient notification of a change, it may be applied > retrospectively, when that has happened, everyone tends to be very aware > that there were bad time conversions for a while. In any case, old > historic stored data isn't affected at all by this kind of change, it > is as valid (or not) after the change as it was before. > You can also have data recorded in the past which refers to the future, so even a change that affects only future timestamps can still invalidate existing stored data. > The second kind of change is a correction to historic data. This happens > when > we discover an error in what was present (and these days, almost only ever > affects pre-1970 timestamps). > > In those, if someone had stored the UTC converted form of some local > timestamp, > then after the correction they wouldn't get back the data that was > originally > used to produce it. > > The problem there is having discarded the original data instead of > retaining > it. Always retain the original source data. Then by all means, when > computing, convert timestamps from their various local values to UTC so > they can be more easily correctly ordered (or whatever) but use those > converted values only for transient computations. Store the original. > Always. > > If that is done correctly, then after a correction to old data, the > results might be different than they were before - but that's only because > they were wrong before, and (hopefully) better after the fix. > I agree 100%. I've been struggling for years to really get my head wrapped around this stuff, and finally decided to create a formal model using abstract data types. I'm finding that approach to be quite helpful, so I wrote it up in a couple of essays that folks on this list might find interesting. In fact, the folks on this list may well be the *only* people who would find them interesting. :-) The first is aimed at the general programmer, but it introduces the fundamental concepts: https://drive.google.com/file/d/1WntAyhIawYtbL2k3fPE71cM9EFkVCJGQ/view?usp=… The second is aimed at time geeks and goes much deeper into the underlying theory: https://drive.google.com/file/d/1aOj9YeDFUST0lQFXZiUsCSmxjnzlbIe4/view?usp=… These are still in draft form, but I hope others find some value in them. (Teaser: the model makes no reference to years, days, hours, or seconds. How's that for abstract?) What is rather interesting (and reassuring) is that the formal model ends up telling us pretty much what this thread has been saying: store original data. However, by looking at things in terms of abstract data types, you can easily see *why* you need to do that without having to resort to specific examples, and many seemingly unrelated cases can be seen to be special cases of the same underlying phenomenon. The model also points you to the very specific places in your design and code where you have to watch out for problems. > The only time it makes sense to store timestamps in other than the original > form is when we *know* that the conversion is correct (and hence, no later > correction will change it). For users of tzdata that really only applies > to post-1970 timestamps. > When exactly do we *know* anything, I mean really for sure? Imagine yourself back in 1966. UTC has been chugging along nicely for five years, providing a well-behaved predictable time standard. We know it's never going to change. Now it's 1967. Oops, the name just changed. Well, that doesn't really count, a rose by any other name ... Now it's 1972. Oops again, we just added a leap second, and there are more on the way. Sorry unix time_t, your fundamental assumption was just revoked -- and so for the next 50 years, nearly every computer on the planet will stubbornly refuse to accept the existence of leap seconds. Never say never. > ---------- Forwarded message ---------- > From: Robert Elz <kre(a)munnari.oz.au> > To: Lester Caine <lester(a)lsces.uk> > Cc: tz(a)iana.org > Bcc: > Date: Wed, 03 Jun 2020 23:48:42 +0700 > Subject: Re: [tz] How good is pre-1970 time zone history represented in TZ > database? > Date: Wed, 3 Jun 2020 16:02:45 +0100 > From: Lester Caine <lester(a)lsces.uk> > Message-ID: <3b7f0c78-4dd7-0f2e-a8e3-2b24401e7e1c(a)lsces.uk> > > | I came into this 20 years ago > > I've been involved with it for longer than that - back to my first > unix experience, in '76, where the US tz rules were compiled into the > code, and most people in AU simply adjusted their computer's clock > (their offset from UTC) 4 times a year (when the US switched summer time > on and off, and when AU did - and yes, that meant that the generated GMT > timestamps were wrong, most of the time). From that (a bit later) I was > responsible for the mess that existed until ado invented tzdata (and yes, > I mean the 2nd arg to gettimeofday()). > You make me look like a newbie. I first got into this seriously in 1997 while updating legacy systems to handle Y2K. > >From all of this I have learned that time is hard. Really hard. > > Many people believe that since they learned to tell the time when > they were 4 or 5 years old, and have been doing it ever since, they > know all there is to know. That's sad... > See the discussion of seduction and polar bears in the first essay linked above. > | now while working with a data archive > | which has now been simply dumped because we had no idea what rules were > | used to produce the normalised data. > > That's a pity, byt sometimes past mistakes simply come back to bite, > and sometimes bite hard. Note that the error there was normalising the > data, if that hadn't been done, none of the rest of it would matter, > you'd now have the original data and could manipulate it however seems > best, for now, regardless of what anyone did with it decades ago (and if > you get it all wrong, future generations could cope, because they'd also > still have the original data, and can fix any errors). > > | Nowadays yes it does make sense to > | store both an original time and a normalised time, > > No, it doesn't, just the original, plus ... > > | along with a location, > > yes, something which can be mapped into a timezone - and as accurate > a location as possible. > > | and a record of which version of rules was used to do the > | normalization. > > Don't care about that, since the result won't be being saved. > > | Add to that a flag that indicates if the UTC time is fixed! > > If the UTC time is the authoritative one, that is what is stored. > No need for extra flags. Just the authoritative time - the one > which defines whatever it is that is being recorded. > I second everything Robert Elz said here. - Michael Kenniston

3 2

[PROPOSED 1/2] zic has new ‘-l -’ and ‘-p -’ options
by Paul Eggert June 13, 2020

June 13, 2020

* NEWS, zic.8: Mention this. * zic.c (dolink): If fromfield is "-", simply remove tofield. --- NEWS | 3 +++ zic.8 | 12 ++++++++++++ zic.c | 5 ++++- 3 files changed, 19 insertions(+), 1 deletion(-) diff --git a/NEWS b/NEWS index 3bcddd0..cdcdbc1 100644 --- a/NEWS +++ b/NEWS @@ -23,6 +23,9 @@ Unreleased, experimental changes Changes to code + zic's new '-l -' and '-p -' options uninstall any existing + localtime and posixrules files, respectively. + The undocumented and ineffective tzsetwall function has been removed. diff --git a/zic.8 b/zic.8 index b1bf437..a431311 100644 --- a/zic.8 +++ b/zic.8 @@ -85,6 +85,12 @@ will act as if the input contained a link line of the form .ti +.5i .ta \w'Link\0\0'u +\w'\fItimezone\fP\0\0'u Link \fItimezone\fP localtime +.sp +If +.I timezone +is +.BR \*- , +any already-existing link is removed. .TP .BI "\*-L " leapsecondfilename Read leap second information from the file with the given name. @@ -109,6 +115,12 @@ and it should not be combined with if .IR timezone 's transitions are at standard time or Universal Time (UT) instead of local time. +.sp +If +.I timezone +is +.BR \*- , +any already-existing link is removed. .TP .BR "\*-r " "[\fB@\fP\fIlo\fP][\fB/@\fP\fIhi\fP]" Reduce the size of output files by limiting their applicability diff --git a/zic.c b/zic.c index 2875b55..c874b04 100644 --- a/zic.c +++ b/zic.c @@ -981,6 +981,7 @@ hardlinkerr(char const *from, char const *to) static void dolink(char const *fromfield, char const *tofield, bool staysymlink) { + bool remove_only = strcmp(fromfield, "-") == 0; bool todirs_made = false; int link_errno; @@ -988,7 +989,7 @@ dolink(char const *fromfield, char const *tofield, bool staysymlink) ** We get to be careful here since ** there's a fair chance of root running us. */ - if (itsdir(fromfield)) { + if (!remove_only && itsdir(fromfield)) { fprintf(stderr, _("%s: link from %s/%s failed: %s\n"), progname, directory, fromfield, strerror(EPERM)); exit(EXIT_FAILURE); @@ -1003,6 +1004,8 @@ dolink(char const *fromfield, char const *tofield, bool staysymlink) progname, directory, tofield, e); exit(EXIT_FAILURE); } + if (remove_only) + return; link_errno = staysymlink ? ENOTSUP : hardlinkerr(fromfield, tofield); if (link_errno == ENOENT && !todirs_made) { mkdirs(tofield, true); -- 2.17.1

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Re: [tz] URLs for DST changes in Hungary (full historical revision)
by Paul Eggert June 9, 2020

June 9, 2020

On 6/9/20 8:16 AM, Nyáry Géza wrote: > Year to year I enclose the URLs being about the changes, I trimmed away the view part of each URL (to keep the URL short) and installed the attached patch to the tzdb sources so that the transitions for Hungary are now much better documented. Thank you for sending us this detailed info.

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How good is pre-1970 time zone history represented in TZ database?
by Alois Treindl June 4, 2020

June 4, 2020

4 10