main.c

linux下的获取Internet time的程式

                k = 1;
            }

/* Count the number of rejected packets and fail if there are too many. */

            if (k) {
                ++rejects;
                if (++rej_level > count)
                    fatal(0,"too many bad or lost packets",NULL);
                else {
                    retry = 1;
                    continue;
                }
            } else
                retry = 0;
            if ((rej_level -= (count < 5 ? count : 5)) < 0) rej_level = 0;
            if (verbose > 2)
                fprintf(stderr,"Offset=%.6f+/-%.6f @ %.6f disp=%.6f\n",
                    offset,error,when,dispersion);
        }
   
/* Calculate the statistics, and display the results or make the initial
correction.  Note that estimate_stats() will return zero if a timestamp
indicates synchronisation loss (usually due to down time or a change of server,
somewhere upstream), and that the recovery operation is unstructured, so great
care should be taken when modifying it.  Also, we want to clear the saved state
is the statistics are bad. */

        handle_saving(save_clear,&total,&index,&cycle,record,&previous,&when,
            &correction);
        ++accepts;
        dispersion = data.dispersion;
        previous = when =
            estimate_stats(&total,&index,record,correction,&dispersion,
                &when,&offset,&error,&drift,&drifterr,&waiting,1);
        if (verbose > 2) {
            fprintf(stderr,"tot=%d ind=%d dis=%.3f when=%.3f off=%.3f ",
                total,index,dispersion,when,offset);
            fprintf(stderr,"err=%.3f wait=%d\n",error,waiting);
        }
        if (when == 0.0) return;
        x = (maxoff < 0.0 ? -maxoff : maxoff);
        if ((offset < 0.0 ? -offset : offset) > x) maxoff = offset;
        correction = 0.0;
        if (operation == op_client || accepts >= count) {
            if (action == action_display) {
                format_time(text,100,offset,error,drift,drifterr);
                printf("%s\n",text);
            } else {
                x = reset_clock(offset,error,1);
                correction += x;
                offset -= x;
            }
        } else
            waiting = delay;
        handle_saving(save_write,&total,&index,&cycle,record,&previous,&when,
            &correction);

/* Now correct the clock for a while, before getting another packet and
updating the statistics. */

        while (when < previous+delay-waiting) {
            do_nothing(waiting);
            if (action == action_display)
                when += waiting;
            else {
                correction += correct_drift(&when,&offset,drift);
                handle_saving(save_write,&total,&index,&cycle,record,
                    &previous,&when,&correction);
            }
        }
continue1: ;
    }
}



int run_client (char *hostnames[], int nhosts, double *server_offset) {

/* Get enough responses to do something with; or not, as the case may be.  Note
that it allows for half of the packets to be bad, so may make up to twice as
many attempts as specified by the -c value.  The deadline checking is merely
paranoia, to protect against broken signal handling - it cannot easily be
triggered if the signal handling works.

This call differs in libmsntp from normal msntp in that it returns the offset
between the local time and the server's time, as seconds, with a fractional
part.
*/

    double history[COUNT_MAX], guesses[COUNT_MAX], offset, error, deadline,
        a, b, x, y;
    int accepts = 0, rejects = 0, flushes = 0, replicates = 0, cycle = 0, k,
        ret;
    unsigned char transmit[NTP_PACKET_MIN];
    ntp_data data;
    char text[100];

    if (verbose > 2) {
        format_time(text,50,0.0,-1.0,0.0,-1.0);
        fprintf(stderr,"Started=%.6f %s\n",current_time(JAN_1970),text);
    }
    for (k = 0; k < nhosts; ++k) open_socket(k,hostnames[k],delay);
    if (action != action_display) {
        set_lock(1);
        locked = 1;
    }
    attempts = 0;
    deadline = current_time(JAN_1970)+delay;

/* Listen to broadcast packets and select the best (i.e. earliest).  This will
be sensitive to a bad NTP broadcaster, but I believe such things are very rare
in practice.  In any case, if you have one, it is probably the only one on your
subnet, so you are knackered!  This allows up to ETHERNET_MAX replications per
packet, for systems with multiple addresses for receiving broadcasts; the only
reason for a limit is to protect against broken NTP servers always returning
the same time. */

    if (operation == op_listen) {
        while (accepts < count) {
            if (current_time(JAN_1970) > deadline) {
                fatal(EMSNTP_UNKNOWN,
                      "not enough valid broadcasts received in time",NULL);
                return EMSNTP_UNKNOWN;
            }
            if (ret = flush_socket(0, &k))
                return ret;
            flushes += k;
            if (read_packet(0,&data,&x,&y)) {
                if (++rejects > count) {
                    fatal(EMSNTP_UNKNOWN,"too many bad or lost packets",NULL);
                    return EMSNTP_UNKNOWN;
                }
                else
                    continue;
            } else {
                a = data.transmit;
                for (k = 0; k < accepts; ++k)
                    if (a == history[k]) {
                        if (++replicates > ETHERNET_MAX*count) {
                            fatal(EMSNTP_UNKNOWN,
                                  "too many replicated packets",NULL);
                            return EMSNTP_UNKNOWN;
                        }
                        goto continue1;
                    }
                history[accepts] = a;
                guesses[accepts++] = x;
            }
            if (verbose > 2)
                fprintf(stderr,"Offset=%.6f disp=%.6f\n",x,dispersion);
            else if (verbose > 1)
                fprintf(stderr,"%s: offset=%.3f disp=%.3f\n",
                    argv0,x,dispersion);

/* Note that bubblesort IS a good method for this amount of data.  */

            for (k = accepts-2; k >= 0; --k)
                if (guesses[k] < guesses[k+1])
                    break;
                else {
                    x = guesses[k];
                    guesses[k] = guesses[k+1];
                    guesses[k+1] = x;
                }
continue1:  ;
        }
        offset = guesses[0];
        error = minerr+guesses[count <= 5 ? count-1 : 5]-offset;
        if (verbose > 2)
            fprintf(stderr,"accepts=%d rejects=%d flushes=%d replicates=%d\n",
                accepts,rejects,flushes,replicates);

/* Handle the client/server model.  It keeps a record of transmitted times,
mainly out of paranoia. */

    } else {
        offset = 0.0;
        error = NTP_INSANITY;
        while (accepts < count && attempts < 2*count) {
            if (current_time(JAN_1970) > deadline) {
                fatal(EMSNTP_TOO_FEW_RESPONSES,
                      "not enough valid responses received in time",NULL);
                return EMSNTP_TOO_FEW_RESPONSES;
            }
            make_packet(&data,NTP_CLIENT);
            outgoing[attempts++] = data.transmit;
            if (verbose > 2) {
                fprintf(stderr,"Outgoing packet on socket %d:\n",cycle);
                display_data(&data);
            }
            pack_ntp(transmit,NTP_PACKET_MIN,&data);
            if (verbose > 2) display_packet(transmit,NTP_PACKET_MIN);
            if (ret = flush_socket(cycle, &k))
                return ret;
            flushes += k;
            write_socket(cycle,transmit,NTP_PACKET_MIN);
            if (read_packet(cycle,&data,&x,&y)) {
                if (++rejects > count) {
                    fatal(EMSNTP_BAD_RESPONSES,
                          "too many bad or lost packets",NULL);
                    return EMSNTP_BAD_RESPONSES;
                }
                else
                    continue;
            } else
                ++accepts;
            if (++cycle >= nhosts) cycle = 0;

/* Work out the most accurate time, and check that it isn't more accurate than
the results warrant. */

            if (verbose > 2)
                fprintf(stderr,"Offset=%.6f+/-%.6f disp=%.6f\n",x,y,dispersion);
            else if (verbose > 1)
                fprintf(stderr,"%s: offset=%.3f+/-%.3f disp=%.3f\n",
                    argv0,x,y,dispersion);
            if ((a = x-offset) < 0.0) a = -a;
            if (accepts <= 1) a = 0.0;
            b = error+y;
            if (y < error) {
                offset = x;
                error = y;
            }
            if (verbose > 2)
                fprintf(stderr,"best=%.6f+/-%.6f\n",offset,error);
            if (a > b) {
                sprintf(text,"%d",cycle);
                fatal(0,"inconsistent times got from NTP server on socket %s",
                        text);
                return EMSNTP_NTP_INCONSISTENCY;
            }
            if (error <= minerr) break;
        }
        if (verbose > 2)
            fprintf(stderr,"accepts=%d rejects=%d flushes=%d\n",
                accepts,rejects,flushes);
    }

/* Tidy up the socket, issues diagnostics and perform the action. */

    for (k = 0; k < nhosts; ++k) close_socket(k);
    if (accepts == 0) {
        fatal(EMSNTP_NO_GOOD_RESPONSE,"no acceptable packets received",NULL);
        return EMSNTP_NO_GOOD_RESPONSE;
    }
    if (error > NTP_INSANITY) {
        fatal(EMSNTP_NTP_INSANITY,
              "unable to get a reasonable time estimate",NULL);
        return EMSNTP_NTP_INSANITY;
    }
    if (verbose > 2)
        fprintf(stderr,"Correction: %.6f +/- %.6f disp=%.6f\n",
            offset,error,dispersion);
    if (action == action_display) {
        format_time(text,75,offset,error,0.0,-1.0);
        printf("%s\n",text);
    } else
        (void)reset_clock(offset,error,0);
    if (locked) set_lock(0);
    if (verbose > 2) fprintf(stderr,"Stopped normally\n");

    *server_offset = offset;
    return 0;
}



int msntp_main (int argc, char *argv[]) {

/* This is the entry point and all that.  It decodes the arguments and calls
one of the specialised routines to do the work. */

    char *hostnames[MAX_SOCKETS], *savename = NULL;
    int daemon = 0, nhosts = 0, help = 0, args = argc-1, k;
    char c;
    double offset;

    if (argv[0] == NULL || argv[0][0] == '\0')
        argv0 = "msntp";
    else if ((argv0 = strrchr(argv[0],'/')) != NULL)
        ++argv0;
    else
        argv0 = argv[0];
    setvbuf(stdout,NULL,_IOLBF,BUFSIZ);
    setvbuf(stderr,NULL,_IOLBF,BUFSIZ);
    if (INT_MAX < 2147483647) fatal(0,"msntp requires >= 32-bit ints",NULL);
    if (DBL_EPSILON > 1.0e-13)
        fatal(0,"msntp requires doubles with eps <= 1.0e-13",NULL);
    for (k = 0; k < MAX_SOCKETS; ++k) hostnames[k] = NULL;

/* Decode the arguments. */

    while (argc > 1) {
        k = 1;
        if (strcmp(argv[1],"-B") == 0 && action == 0) {
            action = action_broadcast;
            if (argc > 2) {
                if (sscanf(argv[2],"%d%c",&period,&c) != 1) syntax(1);
                if (period < 1 || period > 1440)
                    fatal(0,"%s option value out of range","-B");
                period *= 60;
                k = 2;
            } else
                period = 60*60;
        } else if (strcmp(argv[1],"-S") == 0 && action == 0)
            action = action_server;
        else if (strcmp(argv[1],"-q") == 0 && action == 0)
            action = action_query;
        else if (strcmp(argv[1],"-r") == 0 && action == 0)
            action = action_reset;
        else if (strcmp(argv[1],"-a") == 0 && action == 0)
            action = action_adjust;
        else if (strcmp(argv[1],"-l") == 0 && lockname == NULL && argc > 2) {
            lockname = argv[2];
            k = 2;
        } else if ((strcmp(argv[1],"-x") == 0) &&
                daemon == 0) {
            if (argc > 2 && sscanf(argv[2],"%d%c",&daemon,&c) == 1) {
                if (daemon < 1 || daemon > 1440)
                    fatal(0,"%s option value out of range",argv[1]);
                k = 2;
            } else
                daemon = 300;
        } else if (strcmp(argv[1],"-f") == 0 && savename == NULL && argc > 2) {
            savename = argv[2];
            k = 2;
        } else if ((strcmp(argv[1],"--help") == 0 ||
                    strcmp(argv[1],"-h") == 0 || strcmp(argv[1],"-?") == 0) &&
                help == 0)
            help = 1;
        else if (strcmp(argv[1],"-v") == 0 && verbose == 0)
            v