여러대의 컴퓨터에 ping을 날리는 프로그램 구현에 관해서

#include <stdlib.h>
#include <string.h>
#include <stdlib.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <arpa/inet.h>
#include <errno.h>
#include <sys/socket.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/types.h>
 
#define TRY 5
#define ACCEPT 1
#define DROP -1
 
int in_cksum(u_short *p, int n);
 
int ping(char *IP, long to_sec)
{
        int icmp_socket;
        int ret;
        int count = 1;
        int loss = 0;
        int sum_usec = 0;
        int lSelect;
 
        struct icmp *p, *rp;
        struct sockaddr_in addr, from;
        struct ip *ip;
        struct timeval start, end, timeout;
        fd_set s_FD;
 
 
        char buffer[1024];
        int sl;
        int hlen;
        int time_sec, time_usec;
        // ICMP에대응하는 RAW 소켓을 생성한다.
 
        while(count <= TRY)
        {
                timeout.tv_sec = 0;
                timeout.tv_usec = to_sec;
 
                icmp_socket = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
                if(icmp_socket < 0)
                {
                        perror("socket error : ");
                        exit(0);
                }
 
                memset(buffer, 0x00, 1024);
 
                // icmp 패킷을 만든다.
                p = (struct icmp *)buffer;
                p->icmp_type = ICMP_ECHO;
                p->icmp_seq = count;
                p->icmp_code = 0;
                p->icmp_id = getpid();
                p->icmp_cksum = in_cksum((u_short *)p, 1000);
 
                memset(&addr, 0, sizeof(0));
                addr.sin_addr.s_addr = inet_addr(IP);
                addr.sin_family = AF_INET;
 
                // icmp 패킷을 상대 호스트로 전송한다.
                gettimeofday(&start, NULL);
                ret = sendto(icmp_socket,p,sizeof(*p), MSG_DONTWAIT, (struct sockaddr *)&addr, sizeof(addr));
 
                if (ret< 0)
                {
                        perror("sendto error : ");
                }
                sl = sizeof(from);
 
                FD_ZERO(&s_FD);
                FD_SET(icmp_socket, &s_FD);
                lSelect = select(icmp_socket + 1, &s_FD, (fd_set *)0, (fd_set *)0, &timeout);
 
                if (lSelect > 0 && FD_ISSET(icmp_socket, &s_FD) != 0 )
                {
                        // 상대 호스트로 부터 icmp 응답을 기다린다.
                        ret = recvfrom(icmp_socket,buffer, 1024, 0, (struct sockaddr *)&from, &sl);
                        gettimeofday(&end, NULL);
 
                        if (ret < 0)
                        {
                                printf("%d %d %d\n", ret, errno, EAGAIN);
                                perror("recvfrom error : ");
                        }
 
                        // 응답을 받았다면
                        // 해당 호스트의 IP정보와
                        // icmp 패킷 정보를 출력한다.
                        ip = (struct ip *)buffer;
                        hlen = ip->ip_hl*4;
                        rp = (struct icmp *)(buffer+hlen);
 
                        time_sec = end.tv_sec - start.tv_sec;
                        time_usec = (end.tv_usec - start.tv_usec)/1000;
//                      if (!(time_usec < 0))
                        if (count == rp->icmp_seq && !(time_usec < 0) && time_sec == 0)
                        {
                                printf("%d\treply from %s\t", count, inet_ntoa(from.sin_addr));
                                printf("%ld sec %ld ms\t", time_sec, time_usec);
                                printf("Type : %d \t", rp->icmp_type);
                                printf("Code : %d \t", rp->icmp_code);
                                printf("Seq  : %d %d\t", p->icmp_seq, rp->icmp_seq);
                                printf("Iden : %d \n", rp->icmp_id);
                                sum_usec +=time_usec;
                        }
                        else
                        {
                                printf("%d\tRequest Time out : %s\n",count, inet_ntoa(from.sin_addr));
                                loss++;
                                close(icmp_socket);
                                return DROP;
                        }
 
                }
                else
                {
                        printf("%d\tRequest Time out : %s\n",count, inet_ntoa(from.sin_addr));
                        loss++;
                        close(icmp_socket);
                        return DROP;
                }
                count++;
                close(icmp_socket);
        }
        printf("Sent = %d, Received = %d, Lost : %d <%d%% loss>\n", TRY, TRY-loss, loss, (loss/TRY)*100);
}
 
int in_cksum( u_short *p, int n )
{
        register u_short answer;
        register long sum = 0;
        u_short odd_byte = 0;
 
        while( n > 1 )
        {
                sum += *p++;
                n -= 2;
        }
 
        if( n == 1 )
        {
                *( u_char* )( &odd_byte ) = *( u_char* )p;
                sum += odd_byte;
        }
 
        sum = ( sum >> 16 ) + ( sum & 0xffff );
        sum += ( sum >> 16 );
        answer = ~sum;
 
        return ( answer );
}
 
int main(int argc, char **argv[])
{
        if (argc < 2)
        {
                printf("usage : ./ping IP Timeout(ms)\n");
        }
        else
        {
                if (argc == 2)
                {
                        ping((char *)argv[1], (long)100000);
                }
                else
                {
                        ping((char *)argv[1], atol((char *)argv[2]));
                }
        }
        return 0;
}