所以我正在使用需要发送和接收原始以太网帧的设备。它是一种无线电,它使用以太网向其主机发送状态消息。它使用的协议实际上是 IPX,但我认为使用 libpcap 发送原始以太网帧比挖掘实现 IPX 的几十年前的代码更容易(它被 TCP/IP 取代,所以它已经很老了)。
我的程序发送了一个请求包(这个包每次都完全一样,它是无状态的),设备返回一个包含我需要的数据的响应包。我正在使用 pcap_inject 在另一个线程中发送帧和 pcap_loop 来进行接收。我最初将它放在一个线程中,但尝试了 2 个线程以查看它是否解决了我遇到的问题。
问题是 libpcap 似乎没有实时接收数据包。它似乎缓冲了大约 5 个,然后一次处理它们。我希望能够以最快的速度阅读它们。有什么方法可以在 libpcap 上禁用这种缓冲,或者提高刷新率?
一些示例输出(我刚刚打印出接收数据包的时间)。注意每组之间有大约一秒钟的时间
Time: 1365792602.805750
Time: 1365792602.805791
Time: 1365792602.805806
Time: 1365792602.805816
Time: 1365792602.805825
Time: 1365792602.805834
Time: 1365792603.806886
Time: 1365792603.806925
Time: 1365792603.806936
Time: 1365792603.806944
Time: 1365792603.806952
Time: 1365792604.808007
Time: 1365792604.808044
Time: 1365792604.808055
Time: 1365792604.808063
Time: 1365792604.808071
Time: 1365792605.809158
Time: 1365792605.809194
Time: 1365792605.809204
Time: 1365792605.809214
Time: 1365792605.809223
这是注入代码:
char errbuf[PCAP_ERRBUF_SIZE];
char *dev="en0";
if(dev==NULL){
fprintf(stderr,"Pcap error: %s\n",errbuf);
return 2;
}
printf("Device: %s\n",dev);
pcap_t *handle;
handle=pcap_open_live(dev, BUFSIZ, 1, 1000, errbuf);
if(handle==NULL){
fprintf(stderr, "Device open error: %s\n",errbuf);
return 2;
}
//Construct the packet that will get sent to the radio
struct ether_header header;
header.ether_type=htons(0x0170);
int i;
for(i=0;i<6;i++){
header.ether_dhost[i]=radio_ether_address[i];
header.ether_shost[i]=my_ether_address[i];
}
unsigned char frame[sizeof(struct ether_header)+sizeof(radio_request_packet)];
memcpy(frame, &header, sizeof(struct ether_header));
memcpy(frame+sizeof(struct ether_header), radio_request_packet, sizeof(radio_request_packet));
if(pcap_inject(handle, frame, sizeof(frame))==-1){
pcap_perror(handle, errbuf);
fprintf(stderr, "Couldn't send frame: %s\n",errbuf);
return 2;
}
bpf_u_int32 mask;
bpf_u_int32 net;
if(pcap_lookupnet(dev,&net,&mask,errbuf)==-1){
pcap_perror(handle, errbuf);
fprintf(stderr,"Net mask error: %s\n",errbuf);
return 2;
}
char *filter="ether src 00:30:30:01:b1:35";
struct bpf_program fp;
if(pcap_compile(handle, &fp, filter, 0, net)==-1){
pcap_perror(handle, errbuf);
fprintf(stderr,"Filter error: %s\n",errbuf);
return 2;
}
if(pcap_setfilter(handle, &fp)==-1){
pcap_perror(handle, errbuf);
fprintf(stderr, "Install filter error: %s\n",errbuf);
return 2;
}
printf("Starting capture\n");
pthread_t recvThread;
pthread_create(&recvThread, NULL, (void *(*)(void *))thread_helper, handle);
while(1){
if(pcap_inject(handle, frame, sizeof(frame))==-1){
pcap_perror(handle, errbuf);
fprintf(stderr, "Couldn't inject frame: %s\n",errbuf);
return 2;
}
usleep(200000);
}
pcap_close(handle);
return 0;
和接收代码:
void got_packet(u_char *args,const struct pcap_pkthdr * header,const u_char * packet){
struct timeval tv;
gettimeofday(&tv, NULL);
double seconds=(double)tv.tv_sec + ((double)tv.tv_usec)/1000000.0;
printf("Time: %.6f\n",seconds);
}
void *thread_helper(pcap_t *handle){
pcap_loop(handle, -1, got_packet, NULL);
return NULL;
}