4

我正在使用原始套接字编写一个 ping 程序,但即使正在处理 SIGALRM,recvfrom 也没有返回带有 EINTR 的 -1。这个 SIGALRM 是由我的警报(1)产生的。我希望 recvfrom 返回,以便我可以决定数据包确实已经丢失了。

#include "libsock"
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>

double total=0, max=0, min=10000000;
int totalpackets=0, packetslost=0;
int recieved=0;

void handler2()
{
  printf("host unreachable\n");
}

unsigned short 
csum (unsigned short *buf, int nwords)
{
  unsigned long sum;
  for (sum = 0; nwords > 0; nwords--)
    sum += *buf++;
  sum = (sum >> 16) + (sum & 0xffff);
  sum += (sum >> 16);
  return ~sum;
}

void 
handler()
{
  printf("\n");
  printf("--------------PINGING STATISTICS----------------\n");
  printf("AVG:%f MAX:%f MIN:%f TOTAL PACKETS:%d PACKETS LOST:%d SUCCESS PERCENTAGE:%f\n\n",total/(totalpackets-packetslost),max,min,totalpackets,packetslost,((double)(totalpackets-packetslost)/(double)totalpackets)*100);
  exit(0);
}

int 
main (int argc, char *argv[])
{
  if (argc != 2)
  {
    printf ("need destination for tracert\n");
    exit (0);
  }
  int sfd = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
  char buf[4096] = { 0 };

  int one = 1;
  const int *val = &one;
  if (setsockopt (sfd, IPPROTO_IP, IP_HDRINCL, val, sizeof (one)) < 0)
    printf ("Cannot set HDRINCL!\n");

  struct sockaddr_in addr;
  struct ip* ip_hdr=(struct ip*)buf;
  addr.sin_port = htons (7);
  addr.sin_family = AF_INET;
  inet_pton (AF_INET, argv[1], &(addr.sin_addr));

  ip_hdr->ip_hl = 5;
  ip_hdr->ip_v = 4;
  ip_hdr->ip_tos = 0;
  ip_hdr->ip_len = 20 + 8 + 64;
  ip_hdr->ip_id =0;
  ip_hdr->ip_off = 64;
  ip_hdr->ip_ttl = 64;
  ip_hdr->ip_p = IPPROTO_ICMP;
  inet_pton (AF_INET, "172.30.104.59", &(ip_hdr->ip_src));
  inet_pton (AF_INET, argv[1], &(ip_hdr->ip_dst));
  ip_hdr->ip_sum = csum ((unsigned short *) buf, 4);

  struct icmphdr *icmphd = (struct icmphdr *) (buf+20);
  icmphd->type = ICMP_ECHO;
  icmphd->code = 0;
  icmphd->checksum = 0;
  icmphd->un.echo.id = 0;
  icmphd->un.echo.sequence =1;

  memset(buf+28,'a',64);
  icmphd->checksum = csum ((unsigned short *) (buf+20), 36);
  signal(SIGINT,handler);
  struct timeval tv1,tv2;  

  printf("Pinging %s with 64 bytes of data.\n\n",argv[1]);

  while(1)
  {
    recieved=0;     
    totalpackets++;
    sendto (sfd, buf,20+ 8+64, 0, SA & addr, sizeof addr);
    char buff[4096] = { 0 };
    struct sockaddr_in addr2;
    socklen_t len = sizeof (struct sockaddr_in);
    signal(SIGALRM,handler2);
    gettimeofday(&tv1,NULL);
    alarm(1);
    int x=recvfrom (sfd, buff, 20+8+64, 0, SA & addr2, &len);
    gettimeofday(&tv2,NULL);
    double   d=(double)(tv2.tv_sec-tv1.tv_sec)*1000+((double)(tv2.tv_usec-tv1.tv_usec))/1000;

    if(x>0) {
      struct icmphdr *icmphd2 = (struct icmphdr *) (buff + 20);
      printf ("Reached destination:%s\tTime elapsed:%f ms\n\n",
          inet_ntoa (addr2.sin_addr),d);
      total+=d;
      if(d>max)
        max=d;
      if(d<min)
        min=d;
    } else {
      printf("Packet lost\n");   
      packetslost++;
    }

    sleep(1);
  }
  return 0;
}

libsock 包含头文件和 SA=(struct sockaddr*)

SIGALRM 是否与其他信号不同,我没有设置 SA_RESTART..

谢谢。

4

3 回答 3

3

signal的确切行为取决于系统。来自man 2 signal

BSD 语义等价于sigaction(2)使用以下标志调用:

sa.sa_flags = SA_RESTART;

Linux上的情况如下:

...

默认情况下,在 glibc 2 及更高版本中,signal()包装函数不会调用内核系统调用。 相反,它使用提供 BSD 语义的标志调用 sigaction(2)。

(强调我的)

因此,默认情况下,在 Linux 和 BSD 系统上,signal将设置SA_RESTART,这将自动重新启动您的系统调用,使其永远不会报告EINTR.

您需要使用sigaction来精确控制标志:

struct sigaction sact = {
    .sa_handler = handle_sigalrm,
    .sa_flags = 0,
};
sigaction(SIGALRM, &sact, NULL);
于 2013-03-17T16:54:23.913 回答
2

使用“普通”的行为在signal很大程度上取决于操作系统。假设 POSIX 一致性,您应该sigaction改用。请参阅sigaction 和 signal 有什么区别?更多。

于 2013-03-17T16:42:05.947 回答
1

你不应该使用signal,因为它是不可移植的。相反,使用sigaction.

使用选项SA_RESTART,在信号被捕获后,阻塞调用将被静默恢复。没有SA_RESTART,阻塞调用停止,返回 -1 并设置errnoEINTR

这是一个函数mysignal,您可以使用它来替换您的signal呼叫,并将其options设置为 0:

int mysignal (int sig, void (*func)(int), int options) {
  int r; 
  struct sigaction act; 

  act.sa_handler = func; 
  act.sa_flags = options; 
  sigemptyset (&act.sa_mask); 

  r = sigaction (sig, &act, NULL); 
  if (r < 0) perror (__func__); 
  return r;
}
于 2013-03-17T16:46:25.177 回答