Sniffer breaks serial devices

[Jacob]

Hi,

During startup the nRF sniffer extcap script does the following:

def find_sniffer(write_data=False):
    open_ports = list_ports.comports()

    sniffers = []
    for port in [x.device for x in open_ports]:
        for rate in SNIFFER_BAUDRATES:
            reader = None
            try:
                reader = Packet.PacketReader(portnum=port, baudrate=rate)
                try:
                    if write_data:
                        reader.sendPingReq()
                        _ = reader.decodeFromSLIP(0.1, complete_timeout=0.1)
                    else:
                        _ = reader.decodeFromSLIP(0.3, complete_timeout=0.3)

                    # FIXME: Should add the baud rate here, but that will be a breaking change
                    sniffers.append(port.encode('ascii', 'ignore'))
                    break
                except (Exceptions.SnifferTimeout, Exceptions.UARTPacketError):
                    pass
            except (serial.SerialException, ValueError):
                continue
            finally:
                if reader is not None:
                    reader.doExit()
    return sniffers

Which (at least on Linux) breaks applications having open serial ports.

Why not instead use serial.tools.list_ports.comports(? Something like this:

        for port in serial.tools.list_ports.comports():
            if "J-Link - CDC" in port.description:
                return port.device

Thanks, Jacob

[Carles]

Yes, the other alternative is to set your sniffer serial port as belonging to a particular user or user group and give that user or group access to only that serial port. Then run Wireshark as that user/group and it will only ever be able to open the serial port you have assigned for sniffing.

[Jacob]

That doesn't feel like a very "general" solution. Can Nordic add exclusive access to the port when opening? I can't see why it wouldn't be opened that way?

[Carles]

Yes, I can add that patch, I don't see why not. Expect it as part of the next release. Until then you can make the change locally.

[Jacob]

Thanks.

[Carles]

I assume you mean `flock` here when you mean "open with exclusive access". Minicom for example does not see to use that at all and instead creates a /var/lock/LCK../dev/ttyACM*