Wireshark-bugs: [Wireshark-bugs] [Bug 10025] Add dissector for Media Agnostic USB

Date: Tue, 26 Aug 2014 00:31:35 +0000

Comment # 7 on bug 10025 from
(In reply to Bill Meier from comment #6)
> (In reply to Sean O Stalley from comment #5)
> > Created attachment 13015 [details]
> > a trace of MSD enumeration over TCP
> > 
> > Bill:
> > 
> > It also contains instances where MA USB packets span across multiple TCP
> > packets. These don't dissect properly.
> > 
> > I hope this helps,
> > 
> > -Sean
> 
> Thanks
> 
> Yes; while I was reviewing the code (and fixing another bug) I had a
> suspicion that the handling of certain re-assembly cases might not work as
> expected.
> 
> To save me some time, can you indicate the approximate set of frames in the
> capture which aren't being dissected properly (when "USB packets span across
> multiple TCP packets")?

Sure thing, frame 461 is where it starts to get weird. In frame 461, there is 1
complete MAUSB packet (Sequence #22), followed by the start of another MAUSB
packet (sequence #23). frame 462 has part of the packets with sequence numbers
23 & 24. packet 24 is displayed when the packet is complete, but packet 23 is
not.


> Separately, using a global for 'mausb_num_pdus' in general won't work well
> if there happens to be two simultaneous different MAUSB TCP connections in
> the capture. (I don't know if two simultaneous TCP connections in a capture
> would be unlikely; I'll fix it anyway).

There was some discussion about a better way to go about counting PDUs here: 
https://code.wireshark.org/review/#/c/1658/1


It is quite likely that 2 simultaneous MAUSB TCP could be in 1 trace. Consider
the case with 1 Host connected to 2 MAUSB devices. Each device would have a TCP
connection to the host.


> Again separately, I notice that dissection of [GET DESCRIPTOR RESPONSE
> DEVICE]
> MAUSB PDUs (e.g., frame 231) are showing as Malformed. Is this as expected ?

The USB dissectors don't like to dissect partial USB descriptors. For example,
in frame 221 there is only 8 bytes of the device descriptor. That's whats
causing that packet to be malformed.

For the others, it looks like the usb conversation is getting messed up... It
was working previously. I think that's what's causing the other packets to show
up as malformed. I'm investigating that now.


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