tzcode resync

Mark Geisert
Wed Apr 29 09:05:43 GMT 2020

Hi Corinna,

On Wed, 29 Apr 2020, Corinna Vinschen wrote:
> On Apr 29 00:03, Mark Geisert wrote:
>> On Mon, 27 Apr 2020, Corinna Vinschen wrote:
>>> On Apr 24 17:19, Yaakov Selkowitz wrote:
>>>> Our winsup/cygwin/ is a mashup of a very old version of
>>>> upstream tzcode's private.h, tzfile.h, and localtime.c with Cygwin-
>>>> specific patches for getting the timezone from windows as a fallback,
>>>> as well as handling API compatibility with pre-tm_gmtoff binaries.
>>>> The upstream tzcode/tzdata have introduced database changes which
>>>> cannot be read by old code.  Currently, I am building tzdata in the old
>>>> ("rearguard") format to keep compatibility, but at this point we're
>>>> *way* behind upstream and we really should update our code.  Given how
>>>> long it's been though, it's going to be a bit of work.
>>> When I updated back in 2012, I tried to keep it in a format
>>> which allows further updates from the NetBSD version later on.
>>> The last localtime.c update in NetBSD is from 2019.  That should be
>>> sufficient, shouldn't it?
>>> The upstream localtime.c diff from version 1.72 to current 1.122 is
>>> 3K lines of code, so it's still a lot of work, probably...
>> I can take this on.  I've looked at the current NetBSD code diffed against
>> the version we use: there's a fair amount of prototype rejiggering and
>> recoding of localized areas.  New code too, of course.  I've done this kind
>> of thing before and this project seems doable to me.
> Sounds good to me.  I started with this yesterday but didn't make a lot
> of progress, see below.  I'd be happy if you like to take over.

Yes, please :-).

>> I assume I can bring the current NetBSD code directly into Cygwin?  In a
>> legal sense, I mean.
> Yes, that's perfectly fine, given the BSD license.
>> Code-wise I see what Yaakov's suggested and it seems
>> like a great way to go.
> Yesterday eve I was already looking into this and given how NetBSD
> is still under CVS control, I decided trying to pull our
> up from 1.72 to 1.122 version by version, just to be really careful.
> I managed to get up to 1.83 and stumbled over a big problem in terms
> of TZ data format.
> Cygwin has a builtin binary representation of the file "posixrules" in
> tz_posixrules.h.  Since 2000.  And unchanged since 2000!
> This binary representation is used as posixrules data if the posixrules
> file doesn't exist or is unreadable.  I have a vague feeling that this
> data is hopelessly outdated and, probably, the format changed as well.
> So I assume the data in tz_posixrules.h needs either an update, or
> we drop the inline data entirely.
> Dropping this inline data shouldn't be much of a problem, right?
> Cygwin installations shouldn't need it and 3PPs can easily provide
> a posixrules file, I guess...
> Mark, Yaakov, what's your stance in terms of this posixrules data?

I think this is an example of the very thing Yaakov mentioned in the 
quotes above.  Both this internal backup of posixrules and the usual 
posixrules file in /usr/share/zoneinfo are written in the obsolete Version 
0 format.  The current localtime code can only read this version.

When gets updated, it can read Version 2 (there was no 
Version 1 as far as I can tell).  Yaakov will generate V.2 formatted zone 
files at that point.

I can't see a reason to keep this internal backup copy, regardless of 
which Version it is.  But if we do need it, we can generate a V.2 version 
of it once is able to read it.

As I Understand It, for all the above...


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