Re: parent-child process, selectable file descriptor and pcap

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

On Apr 17, 2013, at 7:10 PM, wen lui <esolvepolito () gmail com> wrote:

> I have a program, part of the source codes are:
>
>        handle = pcap_open_live(dev, BUFSIZ, 0, 0, errbuf);
>        pcap_compile(handle, &fp, filter_exp, 0, mask) == -1
>        pcap_setfilter(handle, &fp);
>        struct pcap_pkthdr pcap_header;      // The header that pcap gives
> us
>        const u_char *pcap_packet;           // The actual packet
>
>        while(1){
>
>          n=fork();
>          if(n==0) { // child process

                ...

>                                pcap_packet = pcap_next(pcap_handler, &pcap_header);

> then I notice that the pcap_header.len is 0
> what is the reason for this?

Probably because using the same pcap_t in either a parent and a child, or in two children of the same parent, isn't 
guaranteed to work.

> I think the problem may be:

> 1)   there are parent-child process relationship

Yes.

> can anyone give some suggestions on this? thanks!

Open separate pcap_t's in each process.

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