From: Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
To: Guy Harris <guy-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
Cc: David Young <dyoung-e+AXbWqSrlAAvxtiuMwx3w@public.gmane.org>,
radiotap-S783fYmB3Ccdnm+yROfE0A@public.gmane.org,
Simon Barber <simon-vp0mx6+5gkqFX2APIN6yfw@public.gmane.org>
Subject: Re: [RFC] capture file timestamping
Date: Tue, 25 Aug 2015 19:55:46 +0200 [thread overview]
Message-ID: <1440525346.2192.55.camel@sipsolutions.net> (raw)
In-Reply-To: <4E4FE63E-B636-4808-BBFF-6D2CE4EAFB2F-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
On Tue, 2015-08-25 at 10:47 -0700, Guy Harris wrote:
>
> If you have tcpdump 4.6 or later, with libpcap 1.6 or later, on
> Linux, you should have the --time-stamp-type and --list-time-stamp
> -types options.
>
> If so, what does
>
> > tcpdump --list-time-stamp-types
>
> print?
>
> If it prints "adapter" or "adapter_unsynced", you might want to try
> those with the --time-stamp-type option, as those time stamp types
> mean that the time stamp will come from the adapter rather than from
> Linux. ("unsynced" means that the time stamps aren't synchronized
> with the host's clock.)
It does have "adapter_unsynced", but wouldn't the adapter also have to
support it? Ah, yes, if I do
tcpdump -i wlan0 --list-time-stamp-types
it no longer shows it.
Although perhaps I could possibly convince the driver to report this
timestamp somehow, rather than changing radiotap.
> unless it's based on the TSF (which it probably won't be, as it
> should, at least in principle, be Epoch time, although I think Linux
> may have, at some point, changed adapter time stamps in a fashion
> making them not useful as libpcap time stamps).
That, however, I almost certainly cannot do - I don't see how I'd
synchronize from the adapter time (a free-running 32-bit counter at
microseconds resolution) to the host time.
johannes
next prev parent reply other threads:[~2015-08-25 17:55 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-25 10:07 [RFC] capture file timestamping Johannes Berg
[not found] ` <1440497229.2192.28.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
2015-08-25 16:28 ` David Young
[not found] ` <20150825162841.GR6823-e+AXbWqSrlAAvxtiuMwx3w@public.gmane.org>
2015-08-25 16:46 ` Johannes Berg
[not found] ` <1440521168.2192.50.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
2015-08-25 17:47 ` Guy Harris
[not found] ` <4E4FE63E-B636-4808-BBFF-6D2CE4EAFB2F-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
2015-08-25 17:55 ` Johannes Berg [this message]
2015-08-26 22:48 ` Simon Barber
[not found] ` <55DE4244.9030407-vp0mx6+5gkqFX2APIN6yfw@public.gmane.org>
2015-09-17 16:51 ` Johannes Berg
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1440525346.2192.55.camel@sipsolutions.net \
--to=johannes-cdvu00un1vgdhxzaddlk8q@public.gmane.org \
--cc=dyoung-e+AXbWqSrlAAvxtiuMwx3w@public.gmane.org \
--cc=guy-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org \
--cc=radiotap-S783fYmB3Ccdnm+yROfE0A@public.gmane.org \
--cc=simon-vp0mx6+5gkqFX2APIN6yfw@public.gmane.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).