| 发表于：2007-06-07 16:43:13 楼主 |
前两天遇到一个非常奇怪的问题,在centos 5下用libpcap库来写一个数据包捕捉的小程序,在调用pcap_next_ex函数来捕捉数据包的时候居然不会超时返回,但是在freebsd下面调用又可以返回,真的很奇怪,请帮忙看看问题出在那里,谢谢!
测试程序代码:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <netinet/if_ether.h>
#include <netinet/tcp.h>
#include <pcap.h>
/* default snap length （maximum bytes per packet to capture) */
#define snap_len 1518
/* ethernet headers are always exactly 14 bytes [1] */
#define size_ethernet 14
int main（int argc, char **argv)
{
char *dev = null; /* capture device name */
char errbuf[pcap_errbuf_size+1]; /* error buffer */
pcap_t *descr; /* packet capture descriptor */
char filter_exp[] = "port 19 "; /* filter expression [3] */
struct bpf_program fp; /* compiled filter program （expression) */
bpf_u_int32 maskp; /* subnet mask */
bpf_u_int32 netp; /* ip */
int num_packets = -1; /* number of packets to capture */
struct pcap_pkthdr pkthdr;
struct timeval tv_out;
int capflag = 1;
struct pcap_pkthdr *header ;
const u_char *packet;
dev = pcap_lookupdev（errbuf);
if （dev == null) {
printf（ "pcap_lookupdev error: %s\n ", errbuf);
exit（exit_failure);
}
/* get network number and mask associated with capture device */
if （pcap_lookupnet（dev, &netp, &maskp, errbuf) == -1) {
printf（ "pcap_lookupnet error: %s\n ", errbuf);
exit（exit_failure);
}
/* open capture device */
descr = pcap_open_live（dev, snap_len, 1, 10, errbuf);
if （descr == null) {
printf（ "pcap_open_live failed: %s\n ", errbuf);
exit（exit_failure);
}
/* make sure we 're capturing on an ethernet device [2] */
if （pcap_datalink（descr) != dlt_en10mb) {
printf（ "error: device is not an ethernet\n ");
exit（exit_failure);
}
/* compile the filter expression */
if （pcap_compile（descr, &fp, filter_exp, 0, maskp) == -1) {
printf（ "pcap_compile failed: %s\n ", pcap_geterr（descr));
exit（exit_failure);
}
/* apply the compiled filter */
if （pcap_setfilter（descr, &fp) == -1) {
printf（ "pcap_setfilter failed: %s\n ", pcap_geterr（descr));
exit（exit_failure);
}
printf（ "ready\n ");
packet = pcap_next（descr, &pkthdr);
capflag = pcap_next_ex（descr, &header, （const u_char**)&packet);
printf（ "capture=%d\n ", capflag);
pcap_freecode（&fp);
pcap_close（descr);
printf（ "\ncapture complete.\n ");
return 0;
}
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