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Annotation of 43BSDTahoe/etc/timed/measure.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1983 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution and use in source and binary forms are permitted
        !             6:  * provided that the above copyright notice and this paragraph are
        !             7:  * duplicated in all such forms and that any documentation,
        !             8:  * advertising materials, and other materials related to such
        !             9:  * distribution and use acknowledge that the software was developed
        !            10:  * by the University of California, Berkeley.  The name of the
        !            11:  * University may not be used to endorse or promote products derived
        !            12:  * from this software without specific prior written permission.
        !            13:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            14:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            15:  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            16:  */
        !            17: 
        !            18: #ifndef lint
        !            19: static char sccsid[] = "@(#)measure.c  2.6 (Berkeley) 6/18/88";
        !            20: #endif /* not lint */
        !            21: 
        !            22: #include "globals.h"
        !            23: #include <protocols/timed.h>
        !            24: #include <netinet/in_systm.h>
        !            25: #include <netinet/ip.h>
        !            26: #include <netinet/ip_icmp.h>
        !            27: 
        !            28: #define BIASP          43199999
        !            29: #define BIASN          -43200000
        !            30: #define MODULO         86400000
        !            31: #define PROCESSING_TIME        5       /* ms. to reduce error in measurement */
        !            32: 
        !            33: #define PACKET_IN      1024
        !            34: 
        !            35: extern int id;
        !            36: int measure_delta;
        !            37: extern int sock_raw;
        !            38: static n_short seqno = 0;
        !            39: 
        !            40: /*
        !            41:  * Measures the differences between machines' clocks using
        !            42:  * ICMP timestamp messages.
        !            43:  */
        !            44: 
        !            45: measure(wait, addr)
        !            46: struct timeval *wait;
        !            47: struct sockaddr_in *addr;
        !            48: {
        !            49:        int length;
        !            50:        int status;
        !            51:        int msgcount, trials;
        !            52:        int cc, count;
        !            53:        fd_set ready;
        !            54:        long sendtime, recvtime, histime;
        !            55:        long min1, min2, diff;
        !            56:        register long delta1, delta2;
        !            57:        struct timeval tv1, tout;
        !            58:        u_char packet[PACKET_IN], opacket[64];
        !            59:        register struct icmp *icp = (struct icmp *) packet;
        !            60:        register struct icmp *oicp = (struct icmp *) opacket;
        !            61:        struct ip *ip = (struct ip *) packet;
        !            62: 
        !            63:        min1 = min2 = 0x7fffffff;
        !            64:        status = HOSTDOWN;
        !            65:        measure_delta = HOSTDOWN;
        !            66: 
        !            67: /* empties the icmp input queue */
        !            68:        FD_ZERO(&ready);
        !            69: empty:
        !            70:        tout.tv_sec = tout.tv_usec = 0;
        !            71:        FD_SET(sock_raw, &ready);
        !            72:        if (select(FD_SETSIZE, &ready, (fd_set *)0, (fd_set *)0, &tout)) {
        !            73:                length = sizeof(struct sockaddr_in);
        !            74:                cc = recvfrom(sock_raw, (char *)packet, PACKET_IN, 0, 
        !            75:                    (struct sockaddr_in *)NULL, &length);
        !            76:                if (cc < 0)
        !            77:                        return(-1);
        !            78:                goto empty;
        !            79:        }
        !            80: 
        !            81:        /*
        !            82:         * To measure the difference, select MSGS messages whose round-trip
        !            83:         * time is smaller than RANGE if ckrange is 1, otherwise simply
        !            84:         * select MSGS messages regardless of round-trip transmission time.
        !            85:         * Choose the smallest transmission time in each of the two directions.
        !            86:         * Use these two latter quantities to compute the delta between
        !            87:         * the two clocks.
        !            88:         */
        !            89: 
        !            90:        length = sizeof(struct sockaddr_in);
        !            91:        oicp->icmp_type = ICMP_TSTAMP;
        !            92:        oicp->icmp_code = 0;
        !            93:        oicp->icmp_cksum = 0;
        !            94:        oicp->icmp_id = id;
        !            95:        oicp->icmp_rtime = 0;
        !            96:        oicp->icmp_ttime = 0;
        !            97:        FD_ZERO(&ready);
        !            98:        msgcount = 0;
        !            99:        for (trials = 0; msgcount < MSGS && trials < TRIALS; ++trials) {
        !           100:                oicp->icmp_seq = ++seqno;
        !           101:                oicp->icmp_cksum = 0;
        !           102: 
        !           103:                tout.tv_sec = wait->tv_sec;
        !           104:                tout.tv_usec = wait->tv_usec;
        !           105: 
        !           106:                (void)gettimeofday (&tv1, (struct timezone *)0);
        !           107:                sendtime = oicp->icmp_otime = (tv1.tv_sec % (24*60*60)) * 1000 
        !           108:                                                        + tv1.tv_usec / 1000;
        !           109:                oicp->icmp_cksum = in_cksum((u_short *)oicp, sizeof(*oicp));
        !           110:        
        !           111:                count = sendto(sock_raw, (char *)opacket, sizeof(*oicp), 0, 
        !           112:                                addr, sizeof(struct sockaddr_in));
        !           113:                if (count < 0) {
        !           114:                        status = UNREACHABLE;
        !           115:                        return(-1);
        !           116:                }
        !           117:                for (;;) {
        !           118:                        FD_SET(sock_raw, &ready);
        !           119:                        if ((count = select(FD_SETSIZE, &ready, (fd_set *)0,
        !           120:                            (fd_set *)0, &tout)) <= 0)
        !           121:                                break;
        !           122:                        cc = recvfrom(sock_raw, (char *)packet, PACKET_IN, 0, 
        !           123:                            (struct sockaddr_in *)NULL, &length);
        !           124:                        (void)gettimeofday(&tv1, (struct timezone *)0);
        !           125:                        if (cc < 0)
        !           126:                                return(-1);
        !           127:                        icp = (struct icmp *)(packet + (ip->ip_hl << 2));
        !           128:                        if((icp->icmp_type == ICMP_TSTAMPREPLY) &&
        !           129:                            icp->icmp_id == id && icp->icmp_seq == seqno)
        !           130:                                break;
        !           131:                }
        !           132:                if (count <= 0)
        !           133:                        continue;               /* resend */
        !           134:                recvtime = (tv1.tv_sec % (24*60*60)) * 1000 +
        !           135:                    tv1.tv_usec / 1000;
        !           136:                diff = recvtime - sendtime;
        !           137:                /*
        !           138:                 * diff can be less than 0 aroud midnight
        !           139:                 */
        !           140:                if (diff < 0)
        !           141:                        continue;
        !           142:                msgcount++;
        !           143:                histime = ntohl((u_long)icp->icmp_rtime);
        !           144:                /*
        !           145:                 * a hosts using a time format different from 
        !           146:                 * ms. since midnight UT (as per RFC792) should
        !           147:                 * set the high order bit of the 32-bit time
        !           148:                 * value it transmits.
        !           149:                 */
        !           150:                if ((histime & 0x80000000) != 0) {
        !           151:                        status = NONSTDTIME;
        !           152:                        break;
        !           153:                }
        !           154:                status = GOOD;
        !           155:                delta1 = histime - sendtime;
        !           156:                /*
        !           157:                 * Handles wrap-around to avoid that around 
        !           158:                 * midnight small time differences appear 
        !           159:                 * enormous. However, the two machine's clocks
        !           160:                 * must be within 12 hours from each other.
        !           161:                 */
        !           162:                if (delta1 < BIASN)
        !           163:                        delta1 += MODULO;
        !           164:                else if (delta1 > BIASP)
        !           165:                        delta1 -= MODULO;
        !           166:                delta2 = recvtime - histime;
        !           167:                if (delta2 < BIASN)
        !           168:                        delta2 += MODULO;
        !           169:                else if (delta2 > BIASP)
        !           170:                        delta2 -= MODULO;
        !           171:                if (delta1 < min1)  
        !           172:                        min1 = delta1;
        !           173:                if (delta2 < min2)
        !           174:                        min2 = delta2;
        !           175:                if (diff < RANGE) {
        !           176:                        min1 = delta1;
        !           177:                        min2 = delta2;
        !           178:                        break;
        !           179:                }
        !           180:        }
        !           181: 
        !           182:        /*
        !           183:         * If no answer is received for TRIALS consecutive times, 
        !           184:         * the machine is assumed to be down
        !           185:         */
        !           186:         if (status == GOOD) {
        !           187:                measure_delta = (min1 - min2)/2 + PROCESSING_TIME;
        !           188:        }
        !           189:        return(status);
        !           190: }

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