Re: [PATCH nft] tests: py: use `os.unshare` Python function

[Phil Sutter <phil@nwl.cc>]

Hi Jeremy,

On Fri, Mar 06, 2026 at 06:35:53PM +0000, Jeremy Sowden wrote:
> On 2026-03-06, at 18:41:06 +0100, Phil Sutter wrote:
> >On Thu, Mar 05, 2026 at 05:53:58PM +0000, Jeremy Sowden wrote:
> > > Since Python 3.12 the standard library has included an `os.unshare` function.
> > > Use it if it is available.
> > 
> > This patch breaks py test suite cases involving time-related matches,
> > e.g. 'meta time "1970-05-23 21:07:14"'. It expects:
> > 
> > | cmp eq reg 1 0x002bd503 0x43f05400
> 
> 	$ TZ=UTC-2 perl -MPOSIX=strftime -le 'my $ns = hex $ARGV[0]; print strftime "%Y-%m-%d %H:%M:%S", localtime int $ns / 1000000000' 0x002bd50343f05400
> 	1970-05-23 21:07:14
> 
> > but instead the rule serializes into:
> > 
> > | cmp eq reg 1 0x002bd849 0x74a8f400
> 
> 	$ TZ=UTC-2 perl -MPOSIX=strftime -le 'my $ns = hex $ARGV[0]; print strftime "%Y-%m-%d %H:%M:%S", localtime int $ns / 1000000000' 0x002bd84974a8f400
> 	1970-05-23 22:07:14
> 
> > Do you see that too?
> 
> Yes, e.g.:
> 
> 	6: WARNING: line 4: 'add rule netdev test-netdev egress meta time > "2022-07-01 11:00:00" accept': '[ cmp gt reg 1 0x16fda8f3 0x1977a000 ]' mismatches '[ cmp gt reg 1 0x16fdac39 0x4a304000 ]'
> 
> As with your example, the discrepancy is an hour:
> 
> 	$ TZ=UTC-2 perl -MPOSIX=strftime -le 'my $ns = hex $ARGV[0]; print strftime "%Y-%m-%d %H:%M:%S", localtime int $ns / 1000000000' 0x16fda8f31977a000
> 2022-07-01 11:00:00
> 
> 	$ TZ=UTC-2 perl -MPOSIX=strftime -le 'my $ns = hex $ARGV[0]; print strftime "%Y-%m-%d %H:%M:%S", localtime int $ns / 1000000000' 0x16fdac394a304000
> 2022-07-01 12:00:00
> 
> which suggests it's time-zone related.  Didn't see anything about that
> in the doc's.  Will take a closer look.  Apologies.

Yes, it's odd. Neither unshare module nor 'unshare -n' behave like this,
even though os.unshare is described as doing the same as unshare command
does. It also doesn't mangle os.environ['TZ'] value, no idea why it
messes with this.

> PS UTC-2 is exotic. :)

Maybe it's Ander Juaristi's native timezone, he added the tests in
commit 0518ea3f70d8c ("tests: add meta time test cases"). And then I
did:

commit 7e326d697ecf43ea029de5584e59701eb61ca87e
Author: Phil Sutter <phil@nwl.cc>
Date:   Sat Nov 16 22:32:18 2019 +0100

    tests/py: Set a fixed timezone in nft-test.py
    
    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.
    
    Fixes: 0518ea3f70d8c ("tests: add meta time test cases")
    Signed-off-by: Phil Sutter <phil@nwl.cc>
    Acked-by: Ander Juaristi <a@juaristi.eus>
    Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>

So that's how UTC-2 became py test suite's native timezone. :D

Cheers, Phil