diplodocus.org Git - nmh/blob - sbr/lock_file.c

   1
   2 /*
   3  * lock.c -- routines to lock/unlock files
   4  *
   5  * This code is Copyright (c) 2002, by the authors of nmh.  See the
   6  * COPYRIGHT file in the root directory of the nmh distribution for
   7  * complete copyright information.
   8  */
   9
  10 /* Modified by Ruud de Rooij to support Miquel van Smoorenburg's liblockfile
  11  *
  12  * Since liblockfile locking shares most of its code with dot locking, it
  13  * is enabled by defining both DOT_LOCKING and HAVE_LIBLOCKFILE.
  14  *
  15  * Ruud de Rooij <ruud@debian.org>  Sun, 28 Mar 1999 15:34:03 +0200
  16  */
  17
  18 #include <h/mh.h>
  19 #include <h/signals.h>
  20 #include <h/utils.h>
  21 #include <h/mts.h>
  22
  23 #ifdef HAVE_SYS_TIME_H
  24 # include <sys/time.h>
  25 #endif
  26 #include <time.h>
  27 #include <fcntl.h>
  28 #ifdef HAVE_FLOCK
  29 # include <sys/file.h>
  30 #endif
  31
  32 #if defined(HAVE_LIBLOCKFILE)
  33 # include <lockfile.h>
  34 #endif
  35
  36 #ifdef LOCKDIR
  37 char *lockdir = LOCKDIR;
  38 #endif
  39
  40 /* struct for getting name of lock file to create */
  41 struct lockinfo {
  42     char curlock[BUFSIZ];
  43 #if !defined(HAVE_LIBLOCKFILE)
  44     char tmplock[BUFSIZ];
  45 #endif
  46 };
  47
  48 /*
  49  * Number of tries to retry locking
  50  */
  51 #define LOCK_RETRIES 5
  52
  53 /*
  54  * Amount of time to wait before
  55  * updating ctime of lock file.
  56  */
  57 #define NSECS 20
  58
  59 #if !defined(HAVE_LIBLOCKFILE)
  60 /*
  61  * How old does a lock file need to be
  62  * before we remove it.
  63  */
  64 #define RSECS 180
  65 #endif /* HAVE_LIBLOCKFILE */
  66
  67 /* struct for recording and updating locks */
  68 struct lock {
  69     int l_fd;
  70     char *l_lock;
  71     struct lock *l_next;
  72 };
  73
  74 enum locktype { FCNTL_LOCKING, FLOCK_LOCKING, LOCKF_LOCKING, DOT_LOCKING };
  75
  76 /*
  77  * Flags to indicate whether we've initialized the lock types, and
  78  * our saved lock types
  79  */
  80 static int datalockinit = 0;
  81 static int spoollockinit = 0;
  82 static enum locktype datalocktype, spoollocktype;
  83
  84
  85 /* top of list containing all open locks */
  86 static struct lock *l_top = NULL;
  87
  88 static int lkopen(const char *, int, mode_t, enum locktype);
  89 static int str2accbits(const char *);
  90
  91 static int lkopen_fcntl (const char *, int, mode_t);
  92 #ifdef HAVE_LOCKF
  93 static int lkopen_lockf (const char *, int, mode_t);
  94 #endif /* HAVE_LOCKF */
  95 #ifdef HAVE_FLOCK
  96 static int lkopen_flock (const char *, int, mode_t);
  97 #endif /* HAVE_FLOCK */
  98
  99 static enum locktype init_locktype(const char *);
 100
 101 static int lkopen_dot (const char *, int, mode_t);
 102 static void lkclose_dot (int, const char *);
 103 static void lockname (const char *, struct lockinfo *, int);
 104 static void timerON (char *, int);
 105 static void timerOFF (int);
 106 static void alrmser (int);
 107
 108 #if !defined(HAVE_LIBLOCKFILE)
 109 static int lockit (struct lockinfo *);
 110 #endif
 111
 112 /*
 113  * Base functions: determine the data type used to lock files and
 114  * call the underlying function.
 115  */
 116
 117 int
 118 lkopendata(const char *file, int access, mode_t mode)
 119 {
 120     if (! datalockinit) {
 121         char *cp = context_find("datalocking");
 122
 123         if (cp) {
 124             datalocktype = init_locktype(cp);
 125         } else {
 126             /* We default to fcntl locking for data files */
 127             datalocktype = FCNTL_LOCKING;
 128         }
 129
 130         datalockinit = 1;
 131     }
 132
 133     return lkopen(file, access, mode, datalocktype);
 134 }
 135
 136
 137 /*
 138  * Locking using the spool locking algorithm
 139  */
 140
 141 int lkopenspool(const char *file, int access, mode_t mode)
 142 {
 143     if (! spoollockinit) {
 144         spoollocktype = init_locktype(spoollocking);
 145
 146         spoollockinit = 1;
 147     }
 148
 149     return lkopen(file, access, mode, spoollocktype);
 150 }
 151
 152
 153 /*
 154  * Versions of lkopen that return a FILE *
 155  */
 156
 157 FILE *
 158 lkfopendata(const char *file, const char *mode)
 159 {
 160     FILE *fp;
 161     int oflags = str2accbits(mode);
 162     int fd;
 163
 164     if (oflags == -1) {
 165         errno = EINVAL;
 166         return NULL;
 167     }
 168
 169     if ((fd = lkopendata(file, oflags, 0666)) == -1)
 170         return NULL;
 171
 172     if ((fp = fdopen (fd, mode)) == NULL) {
 173         close (fd);
 174         return NULL;
 175     }
 176
 177     return fp;
 178 }
 179
 180 FILE *
 181 lkfopenspool(const char *file, const char *mode)
 182 {
 183     FILE *fp;
 184     int oflags = str2accbits(mode);
 185     int fd;
 186
 187     if (oflags == -1) {
 188         errno = EINVAL;
 189         return NULL;
 190     }
 191
 192     if ((fd = lkopenspool(file, oflags, 0666)) == -1)
 193         return NULL;
 194
 195     if ((fp = fdopen (fd, mode)) == NULL) {
 196         close (fd);
 197         return NULL;
 198     }
 199
 200     return fp;
 201 }
 202
 203
 204 /*
 205  * Corresponding close functions.
 206  *
 207  * A note here: All of the kernel locking functions terminate the lock
 208  * when the descriptor is closed, so why write the code to explicitly
 209  * unlock the file?  We only need to do this in the dot-locking case.
 210  */
 211
 212 int
 213 lkclosedata(int fd, const char *name)
 214 {
 215     int rc = close(fd);
 216
 217     if (datalocktype == DOT_LOCKING)
 218         lkclose_dot(fd, name);
 219
 220     return rc;
 221 }
 222
 223 int
 224 lkfclosedata(FILE *f, const char *name)
 225 {
 226     int fd, rc;
 227
 228     if (f == NULL)
 229         return 0;
 230
 231     fd = fileno(f);
 232     rc = fclose(f);
 233
 234     if (datalocktype == DOT_LOCKING)
 235         lkclose_dot(fd, name);
 236
 237     return rc;
 238 }
 239
 240 int
 241 lkclosespool(int fd, const char *name)
 242 {
 243     int rc = close(fd);
 244
 245     if (spoollocktype == DOT_LOCKING)
 246         lkclose_dot(fd, name);
 247
 248     return rc;
 249 }
 250
 251 int
 252 lkfclosespool(FILE *f, const char *name)
 253 {
 254     int fd, rc;
 255
 256     if (f == NULL)
 257         return 0;
 258
 259     fd = fileno(f);
 260     rc = fclose(f);
 261
 262     if (spoollocktype == DOT_LOCKING)
 263         lkclose_dot(fd, name);
 264
 265     return rc;
 266 }
 267
 268
 269 /*
 270  * Convert fopen() mode argument to open() bits
 271  */
 272
 273 static int
 274 str2accbits(const char *mode)
 275 {
 276     if (strcmp (mode, "r") == 0)
 277         return O_RDONLY;
 278     else if (strcmp (mode, "r+") == 0)
 279         return O_RDWR;
 280     else if (strcmp (mode, "w") == 0)
 281         return O_WRONLY | O_CREAT | O_TRUNC;
 282     else if (strcmp (mode, "w+") == 0)
 283         return O_RDWR | O_CREAT | O_TRUNC;
 284     else if (strcmp (mode, "a") == 0)
 285         return O_WRONLY | O_CREAT | O_APPEND;
 286     else if (strcmp (mode, "a+") == 0)
 287         return O_RDWR | O_CREAT | O_APPEND;
 288     else {
 289         errno = EINVAL;
 290         return -1;
 291     }
 292 }
 293
 294 /*
 295  * Internal routine to switch between different locking types.
 296  */
 297
 298 static int
 299 lkopen (const char *file, int access, mode_t mode, enum locktype ltype)
 300 {
 301     switch (ltype) {
 302
 303     case FCNTL_LOCKING:
 304         return lkopen_fcntl(file, access, mode);
 305
 306     case DOT_LOCKING:
 307         return lkopen_dot(file, access, mode);
 308
 309 #ifdef HAVE_FLOCK
 310     case FLOCK_LOCKING:
 311         return lkopen_flock(file, access, mode);
 312 #endif /* HAVE_FLOCK */
 313
 314 #ifdef HAVE_LOCKF
 315     case LOCKF_LOCKING:
 316         return lkopen_lockf(file, access, mode);
 317 #endif /* HAVE_FLOCK */
 318
 319     default:
 320         adios(NULL, "Internal locking error: unsupported lock type used!");
 321     }
 322
 323     return -1;
 324 }
 325
 326
 327 /*
 328  * Routine to clean up the dot locking file
 329  */
 330
 331 static void
 332 lkclose_dot (int fd, const char *file)
 333 {
 334     struct lockinfo lkinfo;
 335
 336     lockname (file, &lkinfo, 0);        /* get name of lock file */
 337 #if !defined(HAVE_LIBLOCKFILE)
 338     unlink (lkinfo.curlock);            /* remove lock file      */
 339 #else
 340     lockfile_remove(lkinfo.curlock);
 341 #endif /* HAVE_LIBLOCKFILE */
 342     timerOFF (fd);                      /* turn off lock timer   */
 343 }
 344
 345
 346 /*
 347  * Open and lock a file, using fcntl locking
 348  */
 349
 350 static int
 351 lkopen_fcntl(const char *file, int access, mode_t mode)
 352 {
 353     int fd, i, saved_errno;
 354     struct flock flk;
 355
 356     /*
 357      * The assumption here is that if you open the file for writing, you
 358      * need an exclusive lock.
 359      */
 360
 361     for (i = 0; i < LOCK_RETRIES; i++) {
 362         if ((fd = open(file, access, mode)) == -1)
 363             return -1;
 364
 365         flk.l_start = 0;
 366         flk.l_len = 0;
 367         flk.l_type = (access & O_ACCMODE) == O_RDONLY ? F_RDLCK : F_WRLCK;
 368         flk.l_whence = SEEK_SET;
 369
 370         if (fcntl(fd, F_SETLK, &flk) != -1)
 371             return fd;
 372
 373         saved_errno = errno;
 374         close(fd);
 375         sleep(1);
 376     }
 377
 378     errno = saved_errno;
 379     return -1;
 380 }
 381
 382
 383 /*
 384  * Open and lock a file, using flock locking
 385  */
 386
 387 static int
 388 lkopen_flock(const char *file, int access, mode_t mode)
 389 {
 390     int fd, i, saved_errno, locktype;
 391
 392     /*
 393      * The assumption here is that if you open the file for writing, you
 394      * need an exclusive lock.
 395      */
 396
 397     locktype = (((access & O_ACCMODE) == O_RDONLY) ? LOCK_SH : LOCK_EX) |
 398                                                         LOCK_NB;
 399
 400     for (i = 0; i < LOCK_RETRIES; i++) {
 401         if ((fd = open(file, access, mode)) == -1)
 402             return -1;
 403
 404         if (flock(fd, locktype) != -1)
 405             return fd;
 406
 407         saved_errno = errno;
 408         close(fd);
 409         sleep(1);
 410     }
 411
 412     errno = saved_errno;
 413     return -1;
 414 }
 415
 416
 417 /*
 418  * Open and lock a file, using lockf locking
 419  */
 420
 421 static int
 422 lkopen_lockf(const char *file, int access, mode_t mode)
 423 {
 424     int fd, i, saved_errno, saved_access;
 425
 426     /*
 427      * Two notes:
 428      *
 429      * Because lockf locks start from the current offset, mask off O_APPEND
 430      * and seek to the end of the file later if it was requested.
 431      *
 432      * lockf locks require write access to the file, so always add it
 433      * even if it wasn't requested.
 434      */
 435
 436     saved_access = access;
 437
 438     access &= ~O_APPEND;
 439
 440     if ((access & O_ACCMODE) == O_RDONLY) {
 441         access &= ~O_RDONLY;
 442         access |= O_RDWR;
 443     }
 444
 445     for (i = 0; i < LOCK_RETRIES; i++) {
 446         if ((fd = open(file, access, mode)) == -1)
 447             return -1;
 448
 449         if (lockf(fd, F_TLOCK, 0) != -1) {
 450             /*
 451              * Seek to end if requested
 452              */
 453             if (saved_access & O_APPEND) {
 454                 lseek(fd, 0, SEEK_END);
 455             }
 456             return fd;
 457         }
 458
 459         saved_errno = errno;
 460         close(fd);
 461         sleep(1);
 462     }
 463
 464     errno = saved_errno;
 465     return -1;
 466 }
 467
 468
 469 /*
 470  * open and lock a file, using dot locking
 471  */
 472
 473 static int
 474 lkopen_dot (const char *file, int access, mode_t mode)
 475 {
 476     int fd;
 477     struct lockinfo lkinfo;
 478
 479     /* open the file */
 480     if ((fd = open (file, access, mode)) == -1)
 481         return -1;
 482
 483     /*
 484      * Get the name of the eventual lock file, as well
 485      * as a name for a temporary lock file.
 486      */
 487     lockname (file, &lkinfo, 1);
 488
 489 #if !defined(HAVE_LIBLOCKFILE)
 490     {
 491         int i;
 492         for (i = 0;;) {
 493             /* attempt to create lock file */
 494             if (lockit (&lkinfo) == 0) {
 495                 /* if successful, turn on timer and return */
 496                 timerON (lkinfo.curlock, fd);
 497                 return fd;
 498             } else {
 499                 /*
 500                  * Abort locking, if we fail to lock after 5 attempts
 501                  * and are never able to stat the lock file.
 502                  */
 503                 struct stat st;
 504                 if (stat (lkinfo.curlock, &st) == -1) {
 505                     if (i++ > 5)
 506                         return -1;
 507                     sleep (5);
 508                 } else {
 509                     time_t curtime;
 510                     i = 0;
 511                     time (&curtime);
 512
 513                     /* check for stale lockfile, else sleep */
 514                     if (curtime > st.st_ctime + RSECS)
 515                         unlink (lkinfo.curlock);
 516                     else
 517                         sleep (5);
 518                 }
 519                 lockname (file, &lkinfo, 1);
 520             }
 521         }
 522     }
 523 #else
 524     if (lockfile_create(lkinfo.curlock, 5, 0) == L_SUCCESS) {
 525         timerON(lkinfo.curlock, fd);
 526         return fd;
 527     }
 528     else {
 529         close(fd);
 530         return -1;
 531     }
 532 #endif /* HAVE_LIBLOCKFILE */
 533 }
 534
 535 #if !defined(HAVE_LIBLOCKFILE)
 536 /*
 537  * Routine that actually tries to create
 538  * the lock file.
 539  */
 540
 541 static int
 542 lockit (struct lockinfo *li)
 543 {
 544     int fd;
 545     char *curlock, *tmplock;
 546
 547 #if 0
 548     char buffer[128];
 549 #endif
 550
 551     curlock = li->curlock;
 552     tmplock = li->tmplock;
 553
 554     if ((fd = mkstemp(tmplock)) == -1)
 555         return -1;
 556
 557 #if 0
 558     /* write our process id into lock file */
 559     snprintf (buffer, sizeof(buffer), "nmh lock: pid %d\n", (int) getpid());
 560     write(fd, buffer, strlen(buffer) + 1);
 561 #endif
 562
 563     close (fd);
 564
 565     /*
 566      * Now try to create the real lock file
 567      * by linking to the temporary file.
 568      */
 569     fd = link(tmplock, curlock);
 570     unlink(tmplock);
 571
 572     return (fd == -1 ? -1 : 0);
 573 }
 574 #endif /* HAVE_LIBLOCKFILE */
 575
 576 /*
 577  * Get name of lock file, and temporary lock file
 578  */
 579
 580 static void
 581 lockname (const char *file, struct lockinfo *li, int isnewlock)
 582 {
 583     int bplen, tmplen;
 584     char *bp;
 585     const char *cp;
 586
 587 #if 0
 588     struct stat st;
 589 #endif
 590
 591     if ((cp = strrchr (file, '/')) == NULL || *++cp == 0)
 592         cp = file;
 593
 594     bp = li->curlock;
 595     bplen = 0;
 596 #ifdef LOCKDIR
 597     snprintf (bp, sizeof(li->curlock), "%s/", lockdir);
 598     tmplen = strlen (bp);
 599     bp    += tmplen;
 600     bplen += tmplen;
 601 #else
 602     if (cp != file) {
 603         snprintf (bp, sizeof(li->curlock), "%.*s", (int)(cp - file), file);
 604         tmplen = strlen (bp);
 605         bp    += tmplen;
 606         bplen += tmplen;
 607     }
 608 #endif
 609
 610 #if 0
 611     /*
 612      * mmdf style dot locking.  Currently not supported.
 613      * If we start supporting mmdf style dot locking,
 614      * we will need to change the return value of lockname
 615      */
 616     if (stat (file, &st) == -1)
 617         return -1;
 618
 619     snprintf (bp, sizeof(li->curlock) - bplen, "LCK%05d.%05d",
 620         st.st_dev, st.st_ino);
 621 #endif
 622
 623     snprintf (bp, sizeof(li->curlock) - bplen, "%s.lock", cp);
 624
 625 #if !defined(HAVE_LIBLOCKFILE)
 626     /*
 627      * If this is for a new lock, create a name for
 628      * the temporary lock file for lockit()
 629      */
 630     if (isnewlock) {
 631         if ((cp = strrchr (li->curlock, '/')) == NULL || *++cp == 0)
 632             strncpy (li->tmplock, ",LCK.XXXXXX", sizeof(li->tmplock));
 633         else
 634             snprintf (li->tmplock, sizeof(li->tmplock), "%.*s,LCK.XXXXXX",
 635                      (int)(cp - li->curlock), li->curlock);
 636     }
 637 #endif
 638 }
 639
 640
 641 /*
 642  * Add new lockfile to the list of open lockfiles
 643  * and start the lock file timer.
 644  */
 645
 646 static void
 647 timerON (char *curlock, int fd)
 648 {
 649     struct lock *lp;
 650     size_t len;
 651
 652     lp = (struct lock *) mh_xmalloc (sizeof(*lp));
 653
 654     len = strlen(curlock) + 1;
 655     lp->l_fd = fd;
 656     lp->l_lock = mh_xmalloc (len);
 657     memcpy (lp->l_lock, curlock, len);
 658     lp->l_next = l_top;
 659
 660     if (!l_top) {
 661         /* perhaps SIGT{STP,TIN,TOU} ? */
 662         SIGNAL (SIGALRM, alrmser);
 663         alarm (NSECS);
 664     }
 665
 666     l_top = lp;
 667 }
 668
 669
 670 /*
 671  * Search through the list of lockfiles for the
 672  * current lockfile, and remove it from the list.
 673  */
 674
 675 static void
 676 timerOFF (int fd)
 677 {
 678     struct lock *pp, *lp;
 679
 680     alarm(0);
 681
 682     if (l_top) {
 683         for (pp = lp = l_top; lp; pp = lp, lp = lp->l_next) {
 684             if (lp->l_fd == fd)
 685                 break;
 686         }
 687         if (lp) {
 688             if (lp == l_top)
 689                 l_top = lp->l_next;
 690             else
 691                 pp->l_next = lp->l_next;
 692
 693             free (lp->l_lock);
 694             free (lp);
 695         }
 696     }
 697
 698     /* if there are locks left, restart timer */
 699     if (l_top)
 700         alarm (NSECS);
 701 }
 702
 703
 704 /*
 705  * If timer goes off, we update the ctime of all open
 706  * lockfiles, so another command doesn't remove them.
 707  */
 708
 709 static void
 710 alrmser (int sig)
 711 {
 712     char *lockfile;
 713     struct lock *lp;
 714     NMH_UNUSED (sig);
 715
 716     /* update the ctime of all the lock files */
 717     for (lp = l_top; lp; lp = lp->l_next) {
 718         lockfile = lp->l_lock;
 719 #if !defined(HAVE_LIBLOCKFILE)
 720         {
 721             int j;
 722             if (*lockfile && (j = creat (lockfile, 0600)) != -1)
 723                 close (j);
 724         }
 725 #else
 726     lockfile_touch(lockfile);
 727 #endif
 728     }
 729
 730     /* restart the alarm */
 731     alarm (NSECS);
 732 }
 733
 734
 735 /*
 736  * Return a locking algorithm based on the string name
 737  */
 738
 739 static enum locktype
 740 init_locktype(const char *lockname)
 741 {
 742     if (strcasecmp(lockname, "fcntl") == 0) {
 743         return FCNTL_LOCKING;
 744     } else if (strcasecmp(lockname, "lockf") == 0) {
 745 #ifdef HAVE_LOCKF
 746         return LOCKF_LOCKING;
 747 #else /* ! HAVE_LOCKF */
 748         adios(NULL, "lockf not supported on this system");
 749 #endif /* HAVE_LOCKF */
 750     } else if (strcasecmp(lockname, "flock") == 0) {
 751 #ifdef HAVE_FLOCK
 752         return FLOCK_LOCKING;
 753 #else /* ! HAVE_FLOCK */
 754         adios(NULL, "flock not supported on this system");
 755 #endif /* HAVE_FLOCK */
 756     } else if (strcasecmp(lockname, "dot") == 0) {
 757         return DOT_LOCKING;
 758     } else {
 759         adios(NULL, "Unknown lock type: \"%s\"", lockname);
 760         /* NOTREACHED */
 761         return 0;
 762     }
 763 }