06-02-2009
Libpcap: Set a filter. (C)
Hi
I'm reading about the libpcap documentation. I see that with the function:
pcap_setfilter ( pcap_t *p, struct bpf_program *fp)
we can choose to take one packet instead another.
I read that the struct bpf_program allow us to create a packet filter , ....so if I want just sample some pkts at a given rate, for example I'd like to take 1 packet every 10 (no matter which sourc or dest), have I to set in the right way the struct bpf_program?
Or is there another way?
thx in advance
Dedalus.
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LEARN ABOUT V7
pcap_compile
PCAP_COMPILE(3PCAP) PCAP_COMPILE(3PCAP)
NAME
pcap_compile - compile a filter expression
SYNOPSIS
#include <pcap/pcap.h>
int pcap_compile(pcap_t *p, struct bpf_program *fp,
const char *str, int optimize, bpf_u_int32 netmask);
DESCRIPTION
pcap_compile() is used to compile the string str into a filter program. See pcap-filter(7) for the syntax of that string. program is a
pointer to a bpf_program struct and is filled in by pcap_compile(). optimize controls whether optimization on the resulting code is per-
formed. netmask specifies the IPv4 netmask of the network on which packets are being captured; it is used only when checking for IPv4
broadcast addresses in the filter program. If the netmask of the network on which packets are being captured isn't known to the program,
or if packets are being captured on the Linux "any" pseudo-interface that can capture on more than one network, a value of PCAP_NET-
MASK_UNKNOWN can be supplied; tests for IPv4 broadcast addresses will fail to compile, but all other tests in the filter program will be
OK.
RETURN VALUE
pcap_compile() returns 0 on success and -1 on failure. If -1 is returned, pcap_geterr() or pcap_perror() may be called with p as an argu-
ment to fetch or display the error text.
SEE ALSO
pcap(3PCAP), pcap_setfilter(3PCAP), pcap_freecode(3PCAP), pcap_geterr(3PCAP), pcap-filter(7)
5 April 2008 PCAP_COMPILE(3PCAP)