Re: What is meant by the callback function

["Varuna De Silva" <varunax () gmail com>]

On 9/23/07, Guy Harris <guy () alum mit edu> wrote:
> Varuna De Silva wrote:
>
> Yes, the callback function is in the higher-layer software that uses
> libpcap/WinPcap.  tcpdump, for example, has two callback functions that
> write raw packet data to a capture file and one callback function that
> dissects the packet and prints the dissection; other programs such as
> Wireshark/TShark, snort, etc. have their own callback functions.
>
> The callback function processes the packet data handed to it as the third
> argument, and the packet time stamp and length information in the
> structure passed to it as the second argument.
>
> If you're modifying libpcap to support a new type of capture, you don't
> write the callback function,


I am doing this for my device to be supported by wireshark. As I understand
I dont need to write the callback function??? Please correct me if I am
wrong.

you write code in the read_op routine to call
> the callback function;

Yes, I did so as following, ( I am guilty, of copying it directly from
pcap-septel.c)

int muwis_read(pcap_t *p, int cnt, pcap_handler callback, u_char *user)
{
callback(user, &pcap_header, dp);
:
:
}

As I understand this need to be called for each packet captured.

a pointer to the callback function is passed to the
> read_op routine.

This is the "user" in the above code. Now my question is what will
be this "user" function in my case. That is when I call xxxx_read()
pointer to what function will I have to pass to it as " *user "

Thanks,

Varuna

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