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 60
  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, int *);
  89 static int str2accbits(const char *);
  90
  91 static int lkopen_fcntl (const char *, int, mode_t, int *);
  92 #ifdef HAVE_LOCKF
  93 static int lkopen_lockf (const char *, int, mode_t, int *);
  94 #endif /* HAVE_LOCKF */
  95 #ifdef HAVE_FLOCK
  96 static int lkopen_flock (const char *, int, mode_t, int *);
  97 #endif /* HAVE_FLOCK */
  98
  99 static enum locktype init_locktype(const char *);
 100
 101 static int lkopen_dot (const char *, int, mode_t, int *);
 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, int *failed_to_lock)
 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, failed_to_lock);
 134 }
 135
 136
 137 /*
 138  * Locking using the spool locking algorithm
 139  */
 140
 141 int lkopenspool(const char *file, int access, mode_t mode, int *failed_to_lock)
 142 {
 143     if (! spoollockinit) {
 144         spoollocktype = init_locktype(spoollocking);
 145
 146         spoollockinit = 1;
 147     }
 148
 149     return lkopen(file, access, mode, spoollocktype, failed_to_lock);
 150 }
 151
 152
 153 /*
 154  * Versions of lkopen that return a FILE *
 155  */
 156
 157 FILE *
 158 lkfopendata(const char *file, const char *mode, int *failed_to_lock)
 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, failed_to_lock)) == -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 failed_to_lock = 0;
 186     int fd;
 187
 188     if (oflags == -1) {
 189         errno = EINVAL;
 190         return NULL;
 191     }
 192
 193     if ((fd = lkopenspool(file, oflags, 0666, &failed_to_lock)) == -1)
 194         return NULL;
 195
 196     if ((fp = fdopen (fd, mode)) == NULL) {
 197         close (fd);
 198         return NULL;
 199     }
 200
 201     return fp;
 202 }
 203
 204
 205 /*
 206  * Corresponding close functions.
 207  *
 208  * A note here: All of the kernel locking functions terminate the lock
 209  * when the descriptor is closed, so why write the code to explicitly
 210  * unlock the file?  We only need to do this in the dot-locking case.
 211  */
 212
 213 int
 214 lkclosedata(int fd, const char *name)
 215 {
 216     int rc = close(fd);
 217
 218     if (datalocktype == DOT_LOCKING)
 219         lkclose_dot(fd, name);
 220
 221     return rc;
 222 }
 223
 224 int
 225 lkfclosedata(FILE *f, const char *name)
 226 {
 227     int fd, rc;
 228
 229     if (f == NULL)
 230         return 0;
 231
 232     fd = fileno(f);
 233     rc = fclose(f);
 234
 235     if (datalocktype == DOT_LOCKING)
 236         lkclose_dot(fd, name);
 237
 238     return rc;
 239 }
 240
 241 int
 242 lkclosespool(int fd, const char *name)
 243 {
 244     int rc = close(fd);
 245
 246     if (spoollocktype == DOT_LOCKING)
 247         lkclose_dot(fd, name);
 248
 249     return rc;
 250 }
 251
 252 int
 253 lkfclosespool(FILE *f, const char *name)
 254 {
 255     int fd, rc;
 256
 257     if (f == NULL)
 258         return 0;
 259
 260     fd = fileno(f);
 261     rc = fclose(f);
 262
 263     if (spoollocktype == DOT_LOCKING)
 264         lkclose_dot(fd, name);
 265
 266     return rc;
 267 }
 268
 269
 270 /*
 271  * Convert fopen() mode argument to open() bits
 272  */
 273
 274 static int
 275 str2accbits(const char *mode)
 276 {
 277     if (strcmp (mode, "r") == 0)
 278         return O_RDONLY;
 279     if (strcmp (mode, "r+") == 0)
 280         return O_RDWR;
 281     if (strcmp (mode, "w") == 0)
 282         return O_WRONLY | O_CREAT | O_TRUNC;
 283     if (strcmp (mode, "w+") == 0)
 284         return O_RDWR | O_CREAT | O_TRUNC;
 285     if (strcmp (mode, "a") == 0)
 286         return O_WRONLY | O_CREAT | O_APPEND;
 287     if (strcmp (mode, "a+") == 0)
 288         return O_RDWR | O_CREAT | O_APPEND;
 289
 290     errno = EINVAL;
 291     return -1;
 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         int *failed_to_lock)
 301 {
 302     switch (ltype) {
 303
 304     case FCNTL_LOCKING:
 305         return lkopen_fcntl(file, access, mode, failed_to_lock);
 306
 307     case DOT_LOCKING:
 308         return lkopen_dot(file, access, mode, failed_to_lock);
 309
 310 #ifdef HAVE_FLOCK
 311     case FLOCK_LOCKING:
 312         return lkopen_flock(file, access, mode, failed_to_lock);
 313 #endif /* HAVE_FLOCK */
 314
 315 #ifdef HAVE_LOCKF
 316     case LOCKF_LOCKING:
 317         return lkopen_lockf(file, access, mode, failed_to_lock);
 318 #endif /* HAVE_FLOCK */
 319
 320     default:
 321         adios(NULL, "Internal locking error: unsupported lock type used!");
 322     }
 323
 324     return -1;
 325 }
 326
 327
 328 /*
 329  * Routine to clean up the dot locking file
 330  */
 331
 332 static void
 333 lkclose_dot (int fd, const char *file)
 334 {
 335     struct lockinfo lkinfo;
 336
 337     lockname (file, &lkinfo, 0);        /* get name of lock file */
 338 #if !defined(HAVE_LIBLOCKFILE)
 339     (void) m_unlink (lkinfo.curlock);   /* remove lock file      */
 340 #else
 341     lockfile_remove(lkinfo.curlock);
 342 #endif /* HAVE_LIBLOCKFILE */
 343     timerOFF (fd);                      /* turn off lock timer   */
 344 }
 345
 346
 347 /*
 348  * Open and lock a file, using fcntl locking
 349  */
 350
 351 static int
 352 lkopen_fcntl(const char *file, int access, mode_t mode, int *failed_to_lock)
 353 {
 354     int fd, i, saved_errno;
 355     struct flock flk;
 356
 357     /*
 358      * The assumption here is that if you open the file for writing, you
 359      * need an exclusive lock.
 360      */
 361
 362     for (i = 0; i < LOCK_RETRIES; i++) {
 363         if ((fd = open(file, access, mode)) == -1)
 364             return -1;
 365
 366         flk.l_start = 0;
 367         flk.l_len = 0;
 368         flk.l_type = (access & O_ACCMODE) == O_RDONLY ? F_RDLCK : F_WRLCK;
 369         flk.l_whence = SEEK_SET;
 370
 371         if (fcntl(fd, F_SETLK, &flk) != -1)
 372             return fd;
 373
 374         saved_errno = errno;
 375         close(fd);
 376         sleep(1);
 377     }
 378
 379     *failed_to_lock = 1;
 380     errno = saved_errno;
 381     return -1;
 382 }
 383
 384
 385 #ifdef HAVE_FLOCK
 386 /*
 387  * Open and lock a file, using flock locking
 388  */
 389
 390 static int
 391 lkopen_flock(const char *file, int access, mode_t mode, int *failed_to_lock)
 392 {
 393     int fd, i, saved_errno, locktype;
 394
 395     /*
 396      * The assumption here is that if you open the file for writing, you
 397      * need an exclusive lock.
 398      */
 399
 400     locktype = (((access & O_ACCMODE) == O_RDONLY) ? LOCK_SH : LOCK_EX) |
 401                                                         LOCK_NB;
 402
 403     for (i = 0; i < LOCK_RETRIES; i++) {
 404         if ((fd = open(file, access, mode)) == -1)
 405             return -1;
 406
 407         if (flock(fd, locktype) != -1)
 408             return fd;
 409
 410         saved_errno = errno;
 411         close(fd);
 412         sleep(1);
 413     }
 414
 415     *failed_to_lock = 1;
 416     errno = saved_errno;
 417     return -1;
 418 }
 419 #endif /* HAVE_FLOCK */
 420
 421 /*
 422  * Open and lock a file, using lockf locking
 423  */
 424
 425 static int
 426 lkopen_lockf(const char *file, int access, mode_t mode, int *failed_to_lock)
 427 {
 428     int fd, i, saved_errno, saved_access;
 429
 430     /*
 431      * Two notes:
 432      *
 433      * Because lockf locks start from the current offset, mask off O_APPEND
 434      * and seek to the end of the file later if it was requested.
 435      *
 436      * lockf locks require write access to the file, so always add it
 437      * even if it wasn't requested.
 438      */
 439
 440     saved_access = access;
 441
 442     access &= ~O_APPEND;
 443
 444     if ((access & O_ACCMODE) == O_RDONLY) {
 445         access &= ~O_RDONLY;
 446         access |= O_RDWR;
 447     }
 448
 449     for (i = 0; i < LOCK_RETRIES; i++) {
 450         if ((fd = open(file, access, mode)) == -1)
 451             return -1;
 452
 453         if (lockf(fd, F_TLOCK, 0) != -1) {
 454             /*
 455              * Seek to end if requested
 456              */
 457             if (saved_access & O_APPEND) {
 458                 lseek(fd, 0, SEEK_END);
 459             }
 460             return fd;
 461         }
 462
 463         saved_errno = errno;
 464         close(fd);
 465         sleep(1);
 466     }
 467
 468     *failed_to_lock = 1;
 469     errno = saved_errno;
 470     return -1;
 471 }
 472
 473
 474 /*
 475  * open and lock a file, using dot locking
 476  */
 477
 478 static int
 479 lkopen_dot (const char *file, int access, mode_t mode, int *failed_to_lock)
 480 {
 481     int fd;
 482     struct lockinfo lkinfo;
 483
 484     /* open the file */
 485     if ((fd = open (file, access, mode)) == -1)
 486         return -1;
 487
 488     /*
 489      * Get the name of the eventual lock file, as well
 490      * as a name for a temporary lock file.
 491      */
 492     lockname (file, &lkinfo, 1);
 493
 494 #if !defined(HAVE_LIBLOCKFILE)
 495     {
 496         int i;
 497         for (i = 0; i < LOCK_RETRIES; ++i) {
 498             /* attempt to create lock file */
 499             if (lockit (&lkinfo) == 0) {
 500                 /* if successful, turn on timer and return */
 501                 timerON (lkinfo.curlock, fd);
 502                 return fd;
 503             }
 504
 505             /*
 506              * Abort locking, if we fail to lock after 5 attempts
 507              * and are never able to stat the lock file.  Or, if
 508              * we can stat the lockfile but exceed LOCK_RETRIES
 509              * seconds waiting for it (by falling out of the loop).
 510              */
 511             struct stat st;
 512             if (stat (lkinfo.curlock, &st) == -1) {
 513                 if (i++ > 5) break;
 514                 sleep (1);
 515             } else {
 516                 time_t curtime;
 517                 time (&curtime);
 518
 519                 /* check for stale lockfile, else sleep */
 520                 if (curtime > st.st_ctime + RSECS)
 521                     (void) m_unlink (lkinfo.curlock);
 522                 else
 523                     sleep (1);
 524             }
 525             lockname (file, &lkinfo, 1);
 526         }
 527
 528         *failed_to_lock = 1;
 529         return -1;
 530     }
 531 #else
 532     if (lockfile_create(lkinfo.curlock, 5, 0) == L_SUCCESS) {
 533         timerON(lkinfo.curlock, fd);
 534         return fd;
 535     }
 536
 537     close(fd);
 538     *failed_to_lock = 1;
 539     return -1;
 540 #endif /* HAVE_LIBLOCKFILE */
 541 }
 542
 543 #if !defined(HAVE_LIBLOCKFILE)
 544 /*
 545  * Routine that actually tries to create
 546  * the lock file.
 547  */
 548
 549 static int
 550 lockit (struct lockinfo *li)
 551 {
 552     int fd;
 553     char *curlock, *tmpfile;
 554
 555 #if 0
 556     char buffer[128];
 557 #endif
 558
 559     curlock = li->curlock;
 560
 561     if ((tmpfile = m_mktemp(li->tmplock, &fd, NULL)) == NULL) {
 562         advise(NULL, "unable to create temporary file in %s", li->tmplock);
 563         return -1;
 564     }
 565
 566 #if 0
 567     /* write our process id into lock file */
 568     snprintf (buffer, sizeof(buffer), "nmh lock: pid %d\n", (int) getpid());
 569     write(fd, buffer, strlen(buffer) + 1);
 570 #endif
 571
 572     close (fd);
 573
 574     /*
 575      * Now try to create the real lock file
 576      * by linking to the temporary file.
 577      */
 578     fd = link(tmpfile, curlock);
 579     (void) m_unlink(tmpfile);
 580
 581     return (fd == -1 ? -1 : 0);
 582 }
 583 #endif /* HAVE_LIBLOCKFILE */
 584
 585 /*
 586  * Get name of lock file, and temporary lock file
 587  */
 588
 589 static void
 590 lockname (const char *file, struct lockinfo *li, int isnewlock)
 591 {
 592     int bplen, tmplen;
 593     char *bp;
 594     const char *cp;
 595
 596 #if 0
 597     struct stat st;
 598 #endif
 599
 600     if ((cp = strrchr (file, '/')) == NULL || *++cp == 0)
 601         cp = file;
 602
 603     bp = li->curlock;
 604     bplen = 0;
 605 #ifdef LOCKDIR
 606     snprintf (bp, sizeof(li->curlock), "%s/", lockdir);
 607     tmplen = strlen (bp);
 608     bp    += tmplen;
 609     bplen += tmplen;
 610 #else
 611     if (cp != file) {
 612         snprintf (bp, sizeof(li->curlock), "%.*s", (int)(cp - file), file);
 613         tmplen = strlen (bp);
 614         bp    += tmplen;
 615         bplen += tmplen;
 616     }
 617 #endif
 618
 619 #if 0
 620     /*
 621      * mmdf style dot locking.  Currently not supported.
 622      * If we start supporting mmdf style dot locking,
 623      * we will need to change the return value of lockname
 624      */
 625     if (stat (file, &st) == -1)
 626         return -1;
 627
 628     snprintf (bp, sizeof(li->curlock) - bplen, "LCK%05d.%05d",
 629         st.st_dev, st.st_ino);
 630 #endif
 631
 632     snprintf (bp, sizeof(li->curlock) - bplen, "%s.lock", cp);
 633
 634 #if !defined(HAVE_LIBLOCKFILE)
 635     /*
 636      * If this is for a new lock, create a name for
 637      * the temporary lock file for lockit()
 638      */
 639     if (isnewlock) {
 640         if ((cp = strrchr (li->curlock, '/')) == NULL || *++cp == 0)
 641             strncpy (li->tmplock, ",LCK.XXXXXX", sizeof(li->tmplock));
 642         else
 643             snprintf (li->tmplock, sizeof(li->tmplock), "%.*s,LCK.XXXXXX",
 644                      (int)(cp - li->curlock), li->curlock);
 645     }
 646 #endif
 647 }
 648
 649
 650 /*
 651  * Add new lockfile to the list of open lockfiles
 652  * and start the lock file timer.
 653  */
 654
 655 static void
 656 timerON (char *curlock, int fd)
 657 {
 658     struct lock *lp;
 659
 660     NEW(lp);
 661     lp->l_lock = mh_xstrdup(curlock);
 662     lp->l_fd = fd;
 663     lp->l_next = l_top;
 664
 665     if (!l_top) {
 666         /* perhaps SIGT{STP,TIN,TOU} ? */
 667         SIGNAL (SIGALRM, alrmser);
 668         alarm (NSECS);
 669     }
 670     l_top = lp;
 671 }
 672
 673
 674 /*
 675  * Search through the list of lockfiles for the
 676  * current lockfile, and remove it from the list.
 677  */
 678
 679 static void
 680 timerOFF (int fd)
 681 {
 682     struct lock *pp, *lp;
 683
 684     alarm(0);
 685
 686     if (l_top) {
 687         for (pp = lp = l_top; lp; pp = lp, lp = lp->l_next) {
 688             if (lp->l_fd == fd)
 689                 break;
 690         }
 691         if (lp) {
 692             if (lp == l_top)
 693                 l_top = lp->l_next;
 694             else
 695                 pp->l_next = lp->l_next;
 696
 697             free (lp->l_lock);
 698             free (lp);
 699         }
 700     }
 701
 702     /* if there are locks left, restart timer */
 703     if (l_top)
 704         alarm (NSECS);
 705 }
 706
 707
 708 /*
 709  * If timer goes off, we update the ctime of all open
 710  * lockfiles, so another command doesn't remove them.
 711  */
 712
 713 static void
 714 alrmser (int sig)
 715 {
 716     char *lockfile;
 717     struct lock *lp;
 718     NMH_UNUSED (sig);
 719
 720     /* update the ctime of all the lock files */
 721     for (lp = l_top; lp; lp = lp->l_next) {
 722         lockfile = lp->l_lock;
 723 #if !defined(HAVE_LIBLOCKFILE)
 724         {
 725             int j;
 726             if (*lockfile && (j = creat (lockfile, 0600)) != -1)
 727                 close (j);
 728         }
 729 #else
 730     lockfile_touch(lockfile);
 731 #endif
 732     }
 733
 734     /* restart the alarm */
 735     alarm (NSECS);
 736 }
 737
 738
 739 /*
 740  * Return a locking algorithm based on the string name
 741  */
 742
 743 static enum locktype
 744 init_locktype(const char *lockname)
 745 {
 746     if (strcasecmp(lockname, "fcntl") == 0) {
 747         return FCNTL_LOCKING;
 748     }
 749     if (strcasecmp(lockname, "lockf") == 0) {
 750 #ifdef HAVE_LOCKF
 751         return LOCKF_LOCKING;
 752 #else /* ! HAVE_LOCKF */
 753         adios(NULL, "lockf not supported on this system");
 754 #endif /* HAVE_LOCKF */
 755     }
 756     if (strcasecmp(lockname, "flock") == 0) {
 757 #ifdef HAVE_FLOCK
 758         return FLOCK_LOCKING;
 759 #else /* ! HAVE_FLOCK */
 760         adios(NULL, "flock not supported on this system");
 761 #endif /* HAVE_FLOCK */
 762     }
 763     if (strcasecmp(lockname, "dot") == 0) {
 764         return DOT_LOCKING;
 765     }
 766     adios(NULL, "Unknown lock type: \"%s\"", lockname);
 767     /* NOTREACHED */
 768     return 0;
 769 }