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Annotation of researchv10no/lbin/Mail/lock.c, revision 1.1

1.1     ! root        1: #include <stdio.h>
        !             2: #include <sys/types.h>
        !             3: #include <sys/stat.h>
        !             4: #include "string.h"
        !             5: #include "mail.h"
        !             6: 
        !             7: /* imports */
        !             8: extern char *mktemp();
        !             9: extern int sleep();
        !            10: extern long lseek();
        !            11: 
        !            12: #define FILNAMSIZ 14
        !            13: #define LOCKPREFIX "/tmp/L."
        !            14: #define TMPLNAME "/tmp/mlXXXXXX"
        !            15: static char *UPASROOT = "/usr/lib/upas/";
        !            16: static char *MAILROOT = "/usr/spool/mail/";
        !            17: static char *SMTPQROOT = "/usr/spool/smtpq/";
        !            18: static char *SYSALIAS = "namefiles";
        !            19: static char *USERALIAS = "/lib/names";
        !            20: static int MBOXMODE = 0644;
        !            21: static char lockname[FILNAMSIZ+sizeof("/tmp/")];
        !            22: static char tlockname[FILNAMSIZ+sizeof("/tmp/")];
        !            23: static char tmplname[sizeof(TMPLNAME)];
        !            24: 
        !            25: static void lockbotch();
        !            26: 
        !            27: /*
        !            28:  *  open a file for appending.  if the file doesn't exist, create it.
        !            29:  *  return the file descriptor.
        !            30:  */
        !            31: appendopen(file)
        !            32:        char *file;
        !            33: {
        !            34:        int out;
        !            35:        long lseek();
        !            36: 
        !            37:        lock(file);
        !            38:        out = open(file, 2);
        !            39:        if (out < 0)
        !            40:                out = creat(file, 0666);
        !            41:        else
        !            42:                chmod(file, 0666);
        !            43:        lseek(out, 0L, 2);
        !            44:        return out;
        !            45: }
        !            46: 
        !            47: /*
        !            48:  *  close an append only file
        !            49:  */
        !            50: appendclose(fd)
        !            51:        int fd;
        !            52: {
        !            53:        close(fd);
        !            54:        unlock();
        !            55: }
        !            56: 
        !            57: /*
        !            58:  *  lock and open file.  If the file doesn't exist and mode!=0, create it.
        !            59:  *  return the file descriptor.
        !            60:  */
        !            61: 
        !            62: FILE *
        !            63: lockopen(file, omode, pmode, uid, gid)
        !            64:        char *file;
        !            65:        char *omode;
        !            66:        int pmode;
        !            67: {
        !            68:        FILE *fp;
        !            69:        struct stat sbuf;
        !            70:        int newfile;
        !            71: 
        !            72:        lock(file);
        !            73:        if(stat(file, &sbuf)<0)
        !            74:                newfile = 1;
        !            75:        else
        !            76:                newfile = 0;
        !            77:        fp = fopen(file, omode);
        !            78:        if(fp==NULL){
        !            79:                unlock();
        !            80:                return NULL;
        !            81:        }
        !            82:        if(newfile){
        !            83:                chown(file, uid, gid);
        !            84:                chmod(file, pmode);
        !            85:        }
        !            86:        return fp;
        !            87: }
        !            88: 
        !            89: /*
        !            90:  *  close and unlock a file.
        !            91:  */
        !            92: lockclose(fp)
        !            93:        FILE *fp;
        !            94: {
        !            95:        fclose(fp);
        !            96:        unlock();
        !            97: }
        !            98: 
        !            99: /*
        !           100:  *  reopen a file without losing the lock.
        !           101:  */
        !           102: FILE *
        !           103: lockreopen(file, omode, fp)
        !           104:        char *file;
        !           105:        char *omode;
        !           106:        FILE *fp;
        !           107: {
        !           108:        return freopen(file, omode, fp);
        !           109: }
        !           110: 
        !           111: /*
        !           112:  *  remove ALL locks
        !           113:  */
        !           114: cleanlocks()
        !           115: {
        !           116:        unlock();
        !           117: }
        !           118: 
        !           119: /* break an old lock */
        !           120: static void
        !           121: lockbotch(err, file)
        !           122:        char *err;
        !           123:        char *file;
        !           124: {
        !           125:        int fd;
        !           126:        char msg[128];
        !           127:        char log[256];
        !           128: 
        !           129:        sprintf(msg, "mail: problem with lock file\n");
        !           130:        write(2, msg, strlen(msg));
        !           131:        strcpy(log, MAILROOT);
        !           132:        strcat(log, "mail.log");
        !           133:        if ((fd=open(log, 1)) >= 0) {
        !           134:                sprintf(msg, "error %s (tmp=%s lock=%s)\n", err, file, lockname);
        !           135:                lseek(fd, (long)0, 2);
        !           136:                write(fd, msg, strlen(msg));
        !           137:                close(fd);
        !           138:        }
        !           139: }
        !           140: 
        !           141: /* Fill name with the lock name for file */
        !           142: setlname(name, file)
        !           143:        char *name, *file;
        !           144: {
        !           145:        char *slashp;
        !           146: 
        !           147:        (void)strcpy(name, LOCKPREFIX);
        !           148:        slashp = strrchr(file, '/');
        !           149:        if (slashp==NULL)
        !           150:                strncat(name, file, sizeof(lockname)-strlen(name)-1);
        !           151:        else
        !           152:                strncat(name, slashp+1, sizeof(lockname)-strlen(name)-1);
        !           153:        lockname[sizeof(lockname)-1] = '\0';
        !           154: }
        !           155: 
        !           156: /* Lock the given file */
        !           157: lock(file)
        !           158: char *file;
        !           159: {
        !           160:        int fd, i;
        !           161:        char pidbuf[20];
        !           162: 
        !           163:        /* return if we are already in the middle of a lock */
        !           164:        if (*lockname != '\0') {
        !           165:                lockbotch("double lock", "");
        !           166:                return;
        !           167:        }
        !           168: 
        !           169:        /* create a temporary file */
        !           170:        (void)strcpy(tmplname, TMPLNAME);
        !           171:        (void)mktemp(tmplname);
        !           172:        if ((fd=creat(tmplname, 0444))<0) {
        !           173:                lockbotch("tmp exists", tmplname);
        !           174:                return;
        !           175:        }
        !           176:        sprintf(pidbuf, "%d upas", getpid());
        !           177:        write(fd, pidbuf, strlen(pidbuf));
        !           178:        close(fd);
        !           179: 
        !           180:        /* Make a link to it with the lock file name.  This will fail only
        !           181:         * if it already exists.
        !           182:         */
        !           183:        setlname(lockname, file);
        !           184:        i = 0;
        !           185:        while (link(tmplname, lockname) < 0) {
        !           186:                /* File is already locked */
        !           187:                sleep(2);
        !           188:                (void) islocked(file); /* might break a stale lock */
        !           189:                if (++i > 3000) {
        !           190:                        lockbotch("breaking old lock");
        !           191:                        unlink(lockname);
        !           192:                        link(tmplname, lockname);
        !           193:                        break;
        !           194:                }
        !           195:        }
        !           196:        unlink(tmplname);
        !           197:        *tmplname = '\0';
        !           198:        return;
        !           199: }
        !           200: 
        !           201: /* Return true if file has been locked by us or another program using the same
        !           202:  * lock name scheme.
        !           203:  * But remove the lock file if the locking process has gone away.
        !           204:  */
        !           205: int
        !           206: islocked(file)
        !           207:        char *file;
        !           208: {
        !           209:        struct stat stbuf;
        !           210:        int pid;
        !           211:        FILE *fp;
        !           212: 
        !           213:        setlname(tlockname, file);
        !           214:        if (stat(tlockname, &stbuf)==0) {
        !           215:                fp = fopen(tlockname, "r");
        !           216:                if (fp == NULL || fscanf(fp, "%d", &pid)!=1) {
        !           217:                        /* either we made the lock wrong, or it just went away (race) */
        !           218:                        lockbotch("trouble getting lock pid: breaking lock\n");
        !           219:                        fclose(fp);
        !           220:                        unlink(tlockname);
        !           221:                        return 0;
        !           222:                }
        !           223:                fclose(fp);
        !           224:                if (kill(pid, 0) == 0)
        !           225:                        return 1;
        !           226:                /* locker has gone away */
        !           227:                unlink(tlockname);
        !           228:        }
        !           229:        return 0;
        !           230: }
        !           231: 
        !           232: unlock()
        !           233: {
        !           234:        if (*tmplname != '\0') {
        !           235:                unlink(tmplname);
        !           236:                *tmplname = '\0';
        !           237:        }
        !           238:        if (*lockname != '\0') {
        !           239:                unlink(lockname);
        !           240:                *lockname = '\0';
        !           241:        }
        !           242: }

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