From: Guy Harris <guy-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
To: Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
Cc: "Harald Welte" <laforge-TgoAw6mPHtdg9hUCZPvPmw@public.gmane.org>,
openbsc-qjLDD68F18N4m7O/Vxda39i2O/JbrIOy@public.gmane.org,
radiotap-S783fYmB3Ccdnm+yROfE0A@public.gmane.org,
linux-wireless-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
"Subash Abhinov Kasiviswanathan"
<subashab-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>,
"Dan Williams" <dcbw-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"Bjørn Mork" <bjorn-yOkvZcmFvRU@public.gmane.org>,
netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
"Sean Tranchetti"
<stranche-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>,
"Aleksander Morgado"
<aleksander-Dvg4H30XQSRVIjRurl1/8g@public.gmane.org>
Subject: Re: gsmtap design/extensions?
Date: Fri, 12 Apr 2019 12:48:54 -0700 [thread overview]
Message-ID: <1089142F-2966-4C41-921B-465FBA721E79__45392.3745475308$1555103635$gmane$org@alum.mit.edu> (raw)
In-Reply-To: <1462659018bc40830efbe2348791b8df45b54cff.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
On Apr 12, 2019, at 5:24 AM, Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org> wrote:
> On Thu, 2019-04-11 at 01:32 +0200, Harald Welte wrote:
>
>> GSMTAP was designed as a format to encapsulate protocols normally not spoken over IP
>> (such as classic GSM radio protocols, e.g. the Layer 2 LAPDm over GSM Um)
>> inside an IP transport.
>
> Sure, but wifi is also not spoken over IP, yet we don't encapsulate our
> 802.11 frames into IP to show them in wireshark :-)
That's just because the rpcap protocol hasn't been revved yet to handle the new create/set options/activate mechanism in libpcap to allow monitor-mode capturing, so you only get to see fake Ethernet frames. :-)
I.e., there's a split there between "capture" and "getting the packets from a capture delivered to you over an IP network".
Perhaps there should be a GSMTAP link-layer header type, so you can have a GSMTAP pcap file or GSMTAP interface in a pcapng file, combined with a more general "remote capture" mechanism in libpcap so that you could capture on gsmtap://host:port and capture from a host using the GSMTAP-over-UDP encapsulation - or capture using rpcap.
>> No userspace source would ever be able to generate such data and stream
>> it real-time into wireshark, would it? Sure, I can write pcap file with
>> such ARPHDR_* values, but I could never do this in real-time. For many
>> but not all use cases, that's really what it is: A vehicle to stream
>> real-time non-IP protocol traces into wireshark so it can visualize
>> the protocol traces.
>
> I think you can pipe a stream into wireshark?
1) You could pipe into libpcap or otherwise have a way for a libpcap module to connect to a user space source and get packets from it.
2) You could pipe a pcap file into tcpdump/Wireshark/etc..
3) You could have an extcap program:
https://www.wireshark.org/docs/wsdg_html_chunked/ChCaptureExtcap.html
provide packets to Wireshark.
> To me it feels like the wrong thing to actually make wireshark listen on
> "lo" or "eth0" or something to get data from the cellular that's
> (locally) generated by another application, but I guess that's only
> about how you think about it - and if it's not generated locally then
> that's an easy transport. I'm not sure it makes *sense* because then you
> need permissions to capture on the wired network etc.
Depending on how your system is set up:
$ ls -l /dev/bpf*
crw-rw---- 1 root access_bpf 23, 0 Apr 10 22:57 /dev/bpf0
crw-rw---- 1 root access_bpf 23, 1 Apr 10 22:56 /dev/bpf1
...
and it could just be rw-rw-rw-. Perhaps other systems make it harder to grant capture privileges.
> where you don't *really* need that for this stream
If there's a need for that, whatever provides the packets could impose that (by finding out the UID/GID of the other process if this is going over a UNIX-domain socket, at least on some UN*Xes, or by requiring a login if this is going over a network).
next prev parent reply other threads:[~2019-04-12 19:48 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-09 13:50 gsmtap design/extensions? Johannes Berg
[not found] ` <CAPEnp=bHTVARr7WA9Qkq4=y7kk8_FLWhrkqKOEXubMO4X=BHCw@mail.gmail.com>
[not found] ` <CAPEnp=bHTVARr7WA9Qkq4=y7kk8_FLWhrkqKOEXubMO4X=BHCw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-04-10 7:23 ` Johannes Berg
[not found] ` <46474c61d7748042cc0a1f23773186786020638e.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
2019-04-10 7:57 ` Marcel Holtmann
2019-04-10 23:45 ` Harald Welte
[not found] ` <6F1998DC-EFD2-4145-BD81-A80F9DC7ED2D@holtmann.org>
[not found] ` <6F1998DC-EFD2-4145-BD81-A80F9DC7ED2D-kz+m5ild9QBg9hUCZPvPmw@public.gmane.org>
2019-04-12 12:12 ` Johannes Berg
[not found] ` <1d64c578cd5b254d301cf1cac82f32a062916888.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
2019-04-12 19:49 ` Marcel Holtmann
[not found] ` <D4D12CF9-9CE5-46FB-9738-F89DB6B6F9EA@holtmann.org>
[not found] ` <D4D12CF9-9CE5-46FB-9738-F89DB6B6F9EA-kz+m5ild9QBg9hUCZPvPmw@public.gmane.org>
2019-04-15 9:11 ` Johannes Berg
[not found] ` <92e8e142b6d441c1c995abc57d64ad7b7747a688.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
2019-04-15 10:29 ` Bjørn Mork
[not found] ` <87d0ln1s0a.fsf-3F4PFWf5pNjpjLOzFPqGjWGXanvQGlWp@public.gmane.org>
2019-04-15 10:41 ` Johannes Berg
[not found] ` <20190410234555.GO25552@nataraja>
2019-04-12 17:15 ` Johannes Berg
[not found] ` <f0a64bb751b8c601f58130a7f3a3158d70f18f63.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
2019-04-12 19:54 ` Guy Harris
2019-04-13 7:12 ` Harald Welte
2019-04-13 7:49 ` Guy Harris
[not found] ` <196E881D-AB4A-4569-9C1F-5BCB41FE832F@alum.mit.edu>
[not found] ` <196E881D-AB4A-4569-9C1F-5BCB41FE832F-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
2019-04-12 22:47 ` Guy Harris
[not found] ` <1D6FE33B-DC15-47D8-A1AD-E95608300FDC-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
2019-04-13 6:41 ` Harald Welte
[not found] ` <20190413064152.GB24451@nataraja>
2019-04-13 7:36 ` Guy Harris
[not found] ` <cf07ae24c436f92769f9289d208f01846ebe8826.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
2019-04-10 6:35 ` Vadim Yanitskiy
2019-04-10 23:32 ` Harald Welte
2019-04-12 12:24 ` Johannes Berg
[not found] ` <1462659018bc40830efbe2348791b8df45b54cff.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
2019-04-12 19:48 ` Guy Harris [this message]
2019-04-13 7:35 ` Harald Welte
[not found] ` <20190413073505.GD24451@nataraja>
2019-04-13 7:55 ` Guy Harris
2019-04-15 9:26 ` Johannes Berg
[not found] ` <1089142F-2966-4C41-921B-465FBA721E79@alum.mit.edu>
[not found] ` <1089142F-2966-4C41-921B-465FBA721E79-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
2019-04-15 9:28 ` Johannes Berg
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