안녕하세요 리눅스에서 socket 프로그램 작성에 있어 궁금한점이 있어 문의드립니다.

#define TIME_LOOP_WAIT          200000      // 200ms
#define COUNT_CHECK_LOOP        5
#define SIZE_ICMP_PACKET        64
 
 
struct ICMP_PACKET {
    struct icmphdr hdr;
    char msg[SIZE_ICMP_PACKET - sizeof(struct icmphdr)];
} typedef ICMP_PACKET_t;
 
 
unsigned short checksum(void* _data, int _length) 
{
    unsigned short* p_data;
    unsigned short result;
    unsigned int   sum = 0;
 
    p_data = (unsigned short*)_data;
 
    for (sum = 0; _length > 1; _length -= 2) 
    {
        sum += *p_data++;
    }
 
    if( _length == 1 ) 
    {
        sum += *(unsigned char*)p_data;
    }
 
    sum = (sum >> 16) + (sum & 0xFFFF);
    sum += (sum >> 16);
    result = ~sum;
 
    return result;
}
 
bool class_socket::icmp(socketOption_t& socketOption, std::string _address) 
{
    const int sock_value = 255;
 
    int socket_fd;
    int num_sequence = 1;
    int pid = getpid();
    int idx;
 
    struct sockaddr_in r_addr;
    struct hostent *hname;
    struct sockaddr_in addr_ping,*addr;
 
    ICMP_PACKET_t pckt;
 
    int size_packet_msg = sizeof(pckt.msg);
 
    struct protoent *t_proto = NULL;
    socklen_t len;
 
    t_proto = getprotobyname("ICMP");
 
    hname = gethostbyname(_address.c_str());
 
    bzero(&addr_ping, sizeof(addr_ping));
 
    addr_ping.sin_family = hname->h_addrtype;
    addr_ping.sin_port   = 0;
    addr_ping.sin_addr.s_addr = *(long*)hname->h_addr;
 
    addr = &addr_ping;
 
    int sd;
 
    if( (socket_fd = socket(PF_INET, SOCK_RAW, t_proto->p_proto)) < 0 ) {
        printf("icmp() socket open failed : [%02d] %s\n", errno, strerror(errno));
        return false;
    }
 
    if( setsockopt(socket_fd, SOL_IP, IP_TTL, &sock_value, sizeof(sock_value)) != 0) {
        printf("icmp() set TTL option failed : [%02d] %s\n", errno, strerror(errno));
        return false;
    }
 
    if ( fcntl(socket_fd, F_SETFL, O_NONBLOCK) != 0 ) {
        printf("icmp() request nonblocking I/O failed : [%02d] %s\n", errno, strerror(errno));
        return false;
    }
 
 
    for( int loop_cnt = 0 ; loop_cnt < COUNT_CHECK_LOOP ; loop_cnt++ ) {
        len = sizeof(r_addr);
        if( recvfrom(socket_fd, &pckt, sizeof(pckt), 0x00, (struct sockaddr*)&r_addr, &len) > 0 ) {
 
            close(socket_fd);
            return true;
        }
 
        bzero(&pckt, sizeof(pckt));
        pckt.hdr.type = ICMP_ECHO;
        pckt.hdr.un.echo.id = pid;
 
        for( idx = 0; idx < size_packet_msg - 1 ; idx++ ) {
            pckt.msg[idx] = idx + '0';
        }
 
        pckt.msg[idx] = 0;
        pckt.hdr.un.echo.sequence = num_sequence++;
        pckt.hdr.checksum = checksum(&pckt, sizeof(pckt));
 
        if( sendto(socket_fd, &pckt, sizeof(pckt), 0, (struct sockaddr*)addr, sizeof(*addr)) <= 0 ) 
        {
            printf("icmp() sendto failed : [%02d] %s\n", errno, strerror(errno));
        }
 
        usleep(TIME_LOOP_WAIT);
    }
 
    close(socket_fd);
    return false;
}