[tcpdump-workers] Should the tcpdump tests be run with TZ=GMT0, or should the AFS printer print time stamps in UTC?

Francois-Xavier Le Bail devel.fx.lebail at orange.fr
Mon Aug 6 08:52:05 EDT 2018


On 06/08/2018 10:42, Denis Ovsienko wrote:
>  ---- On Sun, 05 Aug 2018 18:21:47 +0100 John Hawkinson <jhawk at MIT.EDU> wrote ---- 
>  > Denis Ovsienko <denis at ovsienko.info> wrote on Sun,  5 Aug 2018 
>  > at 17:05:20 +0100 in <1650ad5fd29.b5d2798f311917.536858429581803402 at ovsienko.info>: 
>  > > I understand what you are suggesting, and your description is 
>  > > correct, but it does not solve the problem of interpreting tcpdump 
>  > > output correctly in a place or time different from the 
>  > > original. That said, I can live with print-rx.c using local time and 
>  > > being imperfect, it has worked like this many years. Still, I think 
>  > > local time should not be the norm for other decoders. 
>  >  
>  > Doesn't this argument apply for other decoders as well? Whatever is done should not make the output of decoders harder for the diagnostic users of tcpdump to interpret, or unnecessarily change the output format. 
> 
> The factor of consistency does indeed apply, and some decoders use UTC already, whilst some others seem to use local time and to fail the tests from time to time.

> Which reminds us that at the end of the day somebody will need to fix the AFS test, whatever is the consensus.

With the rx packet (#4 in the file) showing the problem, in the current printing (CEST),
the capture time is '23:46:24' and the StoreStatus date is '22:46:24'. difference -1 hour.
And with TZ=GMT0,
The capture time is '21:46:24' (-2: OK) and the StoreStatus date is '21:46:24' (-1). same.

Does anyone understand why?
---------------------------------------------------------------------------------------------------
$ ./tcpdump -#ttttnv -r tests/afs.pcap|grep -B1 'StoreStatus date'
reading from file tests/afs.pcap, link-type EN10MB (Ethernet)
    4  1999-11-11 23:46:24.151512 IP (tos 0x0, ttl 64, id 57928, offset 0, flags [none], proto UDP
(17), length 108)
    131.151.32.21.7001 > 131.151.1.59.7000:  rx data seq 1 ser 433 fs call makedir fid 536871098/1/1
"tmpdir" StoreStatus date 1999/11/11 22:46:24 group 0 mode 755 (80)
---------------------------------------------------------------------------------------------------
$ TZ=GMT0 ./tcpdump -#ttttnv -r tests/afs.pcap|grep -B1 'StoreStatus date'
reading from file tests/afs.pcap, link-type EN10MB (Ethernet)
    4  1999-11-11 21:46:24.151512 IP (tos 0x0, ttl 64, id 57928, offset 0, flags [none], proto UDP
(17), length 108)
    131.151.32.21.7001 > 131.151.1.59.7000:  rx data seq 1 ser 433 fs call makedir fid 536871098/1/1
"tmpdir" StoreStatus date 1999/11/11 21:46:24 group 0 mode 755 (80)

-- 
Francois-Xavier


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