Re: Serial port configuration parameters

[Guy Harris <guy () alum mit edu>]

On May 13, 2010, at 12:57 PM, Edgar, Thomas wrote:

> I have updated libpcap to capture traffic from serial COM ports.  However, in order to do this I needed to configure 
> the serial port settings before starting the capture.  The method I have working is to add the port settings 
> variables to the pcap structure.  However, this required a change to the libpcap API by not calling the activate 
> function during the pcap_open_live function if it is a serial port interface and adding a second 
> pcap_configure_serial function that accepts the serial port settings as arguments and then calls the activate 
> function.
>
> Is there a better way to do this so that I can avoid changing the main API?

Not without...
 
> I prefer keeping it within the API and not a config file or something

...having it get the configuration information from somewhere that doesn't involve the API, such as a configuration 
file (ugly) or an environment variable (arguably uglier).

My inclination would be to

        1) encourage anybody who wants to capture on a serial device to use pcap_create() and pcap_activate() (they're 
not going to be able to do it on versions of libpcap without your changes, and unless you backport them to a pre-1.0 
version, that means they're not going to be able to do it on a version of libpcap without pcap_create() and 
pcap_activate()), and have a pcap_set_serial_port_params() routine that's called between pcap_create() and 
pcap_activate();

        2) either set the serial port parameters to "not set yet" values in pcap_create() and have the serial port 
activate routine fail if they're not set, in which case pcap_open_live() will fail on serial ports (as indicated, 
that's no big loss), or set them to default values, in which case pcap_open_live() will use the default values - I'd 
vote for the first of those alternatives.

If you want to use the monitor mode support, or to set the buffer size, in libpcap, you have to use pcap_create() and 
pcap_activate(); I think it's no loss to require that you use them to capture on serial ports.-
This is the tcpdump-workers list.
Visit https://cod.sandelman.ca/ to unsubscribe.