Re: [nft PATCH] tests/py: Set a fixed timezone in nft-test.py

[Phil Sutter <phil@nwl.cc>]

Hi,

On Tue, Nov 19, 2019 at 11:12:36PM +0100, Pablo Neira Ayuso wrote:
> On Tue, Nov 19, 2019 at 12:06:23PM +0100, Ander Juaristi wrote:
> > El 2019-11-18 19:34, Pablo Neira Ayuso escribió:
> > > Hi Phil,
> > > 
> > > On Sat, Nov 16, 2019 at 10:32:18PM +0100, Phil Sutter wrote:
> > > > Payload generated for 'meta time' matches depends on host's timezone
> > > > and
> > > > DST setting. To produce constant output, set a fixed timezone in
> > > > nft-test.py. Choose UTC-2 since most payloads are correct then, adjust
> > > > the remaining two tests.
> > > 
> > > This means that the ruleset listing for the user changes when daylight
> > > saving occurs, right? Just like it happened to our tests.
> > 
> > It shouldn't, as the date is converted to a timestamp that doesn't take DST
> > into account (using timegm(3), which is Linux-specific).
> > 
> > The problem is that payloads are hard-coded in the tests.
> > 
> > Correct me if I'm missing something.
> 
> I see, so it's just the _snprintf() function in the library. I
> remember we found another problem with these on big endian, it would
> be probably to move them to libnftables at some point.
> 
> Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>

Ah, now that I reread your question, I finally got it. And you're right:
If DST occurs, time values will change. This is clear from looking at
hour_type_print(): Whatever the kernel returned gets cur_tm->tm_gmtoff
added to it. Here, this is either 3600 or 7200 depending on whether DST
is active or not.

The other alternative would be to make kernel DST-aware, I don't think
that's the case.

Cheers, Phil