The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/kern/vfs_lockf.c

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    1 /*      $NetBSD: vfs_lockf.c,v 1.34 2003/10/25 09:13:41 christos Exp $  */
    2 
    3 /*
    4  * Copyright (c) 1982, 1986, 1989, 1993
    5  *      The Regents of the University of California.  All rights reserved.
    6  *
    7  * This code is derived from software contributed to Berkeley by
    8  * Scooter Morris at Genentech Inc.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 3. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      @(#)ufs_lockf.c 8.4 (Berkeley) 10/26/94
   35  */
   36 
   37 #include <sys/cdefs.h>
   38 __KERNEL_RCSID(0, "$NetBSD: vfs_lockf.c,v 1.34 2003/10/25 09:13:41 christos Exp $");
   39 
   40 #include <sys/param.h>
   41 #include <sys/systm.h>
   42 #include <sys/kernel.h>
   43 #include <sys/file.h>
   44 #include <sys/proc.h>
   45 #include <sys/vnode.h>
   46 #include <sys/malloc.h>
   47 #include <sys/fcntl.h>
   48 #include <sys/lockf.h>
   49 
   50 MALLOC_DEFINE(M_LOCKF, "lockf", "Byte-range locking structures");
   51 
   52 /*
   53  * This variable controls the maximum number of processes that will
   54  * be checked in doing deadlock detection.
   55  */
   56 int maxlockdepth = MAXDEPTH;
   57 
   58 #ifdef LOCKF_DEBUG
   59 int     lockf_debug = 0;
   60 #endif
   61 
   62 #define NOLOCKF (struct lockf *)0
   63 #define SELF    0x1
   64 #define OTHERS  0x2
   65 
   66 static int lf_clearlock(struct lockf *, struct lockf **);
   67 static int lf_findoverlap(struct lockf *,
   68             struct lockf *, int, struct lockf ***, struct lockf **);
   69 static struct lockf *lf_getblock(struct lockf *);
   70 static int lf_getlock(struct lockf *, struct flock *);
   71 static int lf_setlock(struct lockf *, struct lockf **, struct simplelock *);
   72 static void lf_split(struct lockf *, struct lockf *, struct lockf **);
   73 static void lf_wakelock(struct lockf *);
   74 
   75 #ifdef LOCKF_DEBUG
   76 static void lf_print(char *, struct lockf *);
   77 static void lf_printlist(char *, struct lockf *);
   78 #endif
   79 
   80 /*
   81  * XXX TODO
   82  * Misc cleanups: "caddr_t id" should be visible in the API as a
   83  * "struct proc *".
   84  * (This requires rototilling all VFS's which support advisory locking).
   85  *
   86  * Use pools for lock allocation.
   87  */
   88 
   89 /*
   90  * If there's a lot of lock contention on a single vnode, locking
   91  * schemes which allow for more paralleism would be needed.  Given how
   92  * infrequently byte-range locks are actually used in typical BSD
   93  * code, a more complex approach probably isn't worth it.
   94  */
   95 
   96 /*
   97  * Do an advisory lock operation.
   98  */
   99 int
  100 lf_advlock(struct vop_advlock_args *ap, struct lockf **head, off_t size)
  101 {
  102         struct flock *fl = ap->a_fl;
  103         struct lockf *lock = NULL;
  104         struct lockf *sparelock;
  105         struct simplelock *interlock = &ap->a_vp->v_interlock;
  106         off_t start, end;
  107         int error = 0;
  108 
  109         /*
  110          * Convert the flock structure into a start and end.
  111          */
  112         switch (fl->l_whence) {
  113         case SEEK_SET:
  114         case SEEK_CUR:
  115                 /*
  116                  * Caller is responsible for adding any necessary offset
  117                  * when SEEK_CUR is used.
  118                  */
  119                 start = fl->l_start;
  120                 break;
  121 
  122         case SEEK_END:
  123                 start = size + fl->l_start;
  124                 break;
  125 
  126         default:
  127                 return EINVAL;
  128         }
  129         if (start < 0)
  130                 return EINVAL;
  131 
  132         /*
  133          * allocate locks before acquire simple lock.
  134          * we need two locks in the worst case.
  135          */
  136         switch (ap->a_op) {
  137         case F_SETLK:
  138         case F_UNLCK:
  139                 /*
  140                  * XXX for F_UNLCK case, we can re-use lock.
  141                  */
  142                 if ((fl->l_type & F_FLOCK) == 0) {
  143                         /*
  144                          * byte-range lock might need one more lock.
  145                          */
  146                         MALLOC(sparelock, struct lockf *, sizeof(*lock),
  147                             M_LOCKF, M_WAITOK);
  148                         if (sparelock == NULL) {
  149                                 error = ENOMEM;
  150                                 goto quit;
  151                         }
  152                         break;
  153                 }
  154                 /* FALLTHROUGH */
  155 
  156         case F_GETLK:
  157                 sparelock = NULL;
  158                 break;
  159 
  160         default:
  161                 return EINVAL;
  162         }
  163 
  164         MALLOC(lock, struct lockf *, sizeof(*lock), M_LOCKF, M_WAITOK);
  165         if (lock == NULL) {
  166                 error = ENOMEM;
  167                 goto quit;
  168         }
  169 
  170         simple_lock(interlock);
  171 
  172         /*
  173          * Avoid the common case of unlocking when inode has no locks.
  174          */
  175         if (*head == (struct lockf *)0) {
  176                 if (ap->a_op != F_SETLK) {
  177                         fl->l_type = F_UNLCK;
  178                         error = 0;
  179                         goto quit_unlock;
  180                 }
  181         }
  182 
  183         if (fl->l_len == 0)
  184                 end = -1;
  185         else
  186                 end = start + fl->l_len - 1;
  187         /*
  188          * Create the lockf structure.
  189          */
  190         lock->lf_start = start;
  191         lock->lf_end = end;
  192         /* XXX NJWLWP 
  193          * I don't want to make the entire VFS universe use LWPs, because
  194          * they don't need them, for the most part. This is an exception,
  195          * and a kluge.
  196          */
  197 
  198         lock->lf_head = head;
  199         lock->lf_type = fl->l_type;
  200         lock->lf_next = (struct lockf *)0;
  201         TAILQ_INIT(&lock->lf_blkhd);
  202         lock->lf_flags = ap->a_flags;
  203         if (lock->lf_flags & F_POSIX) {
  204                 KASSERT(curproc == (struct proc *)ap->a_id);
  205         }
  206         lock->lf_id = (struct proc *)ap->a_id;
  207         lock->lf_lwp = curlwp;
  208                 
  209         /*
  210          * Do the requested operation.
  211          */
  212         switch (ap->a_op) {
  213 
  214         case F_SETLK:
  215                 error = lf_setlock(lock, &sparelock, interlock);
  216                 lock = NULL; /* lf_setlock freed it */
  217                 break;
  218 
  219         case F_UNLCK:
  220                 error = lf_clearlock(lock, &sparelock);
  221                 break;
  222 
  223         case F_GETLK:
  224                 error = lf_getlock(lock, fl);
  225                 break;
  226 
  227         default:
  228                 break;
  229                 /* NOTREACHED */
  230         }
  231 
  232 quit_unlock:
  233         simple_unlock(interlock);
  234 quit:
  235         if (lock)
  236                 FREE(lock, M_LOCKF);
  237         if (sparelock)
  238                 FREE(sparelock, M_LOCKF);
  239 
  240         return error;
  241 }
  242 
  243 /*
  244  * Set a byte-range lock.
  245  */
  246 static int
  247 lf_setlock(struct lockf *lock, struct lockf **sparelock,
  248     struct simplelock *interlock)
  249 {
  250         struct lockf *block;
  251         struct lockf **head = lock->lf_head;
  252         struct lockf **prev, *overlap, *ltmp;
  253         static char lockstr[] = "lockf";
  254         int ovcase, priority, needtolink, error;
  255 
  256 #ifdef LOCKF_DEBUG
  257         if (lockf_debug & 1)
  258                 lf_print("lf_setlock", lock);
  259 #endif /* LOCKF_DEBUG */
  260 
  261         /*
  262          * Set the priority
  263          */
  264         priority = PLOCK;
  265         if (lock->lf_type == F_WRLCK)
  266                 priority += 4;
  267         priority |= PCATCH;
  268         /*
  269          * Scan lock list for this file looking for locks that would block us.
  270          */
  271         while ((block = lf_getblock(lock)) != NULL) {
  272                 /*
  273                  * Free the structure and return if nonblocking.
  274                  */
  275                 if ((lock->lf_flags & F_WAIT) == 0) {
  276                         FREE(lock, M_LOCKF);
  277                         return EAGAIN;
  278                 }
  279                 /*
  280                  * We are blocked. Since flock style locks cover
  281                  * the whole file, there is no chance for deadlock.
  282                  * For byte-range locks we must check for deadlock.
  283                  *
  284                  * Deadlock detection is done by looking through the
  285                  * wait channels to see if there are any cycles that
  286                  * involve us. MAXDEPTH is set just to make sure we
  287                  * do not go off into neverneverland.
  288                  */
  289                 if ((lock->lf_flags & F_POSIX) &&
  290                     (block->lf_flags & F_POSIX)) {
  291                         struct lwp *wlwp;
  292                         struct lockf *waitblock;
  293                         int i = 0;
  294 
  295                         /*
  296                          * The block is waiting on something.  if_lwp will be
  297                          * 0 once the lock is granted, so we terminate the
  298                          * loop if we find this.
  299                          */
  300                         wlwp = block->lf_lwp;
  301                         while (wlwp && (i++ < maxlockdepth)) {
  302                                 waitblock = (struct lockf *)wlwp->l_wchan;
  303                                 /* Get the owner of the blocking lock */
  304                                 waitblock = waitblock->lf_next;
  305                                 if ((waitblock->lf_flags & F_POSIX) == 0)
  306                                         break;
  307                                 wlwp = waitblock->lf_lwp;
  308                                 if (wlwp == lock->lf_lwp) {
  309                                         free(lock, M_LOCKF);
  310                                         return EDEADLK;
  311                                 }
  312                         }
  313                         /*
  314                          * If we're still following a dependancy chain
  315                          * after maxlockdepth iterations, assume we're in
  316                          * a cycle to be safe.
  317                          */
  318                         if (i >= maxlockdepth) {
  319                                 free(lock, M_LOCKF);
  320                                 return EDEADLK;
  321                         }
  322                 }
  323                 /*
  324                  * For flock type locks, we must first remove
  325                  * any shared locks that we hold before we sleep
  326                  * waiting for an exclusive lock.
  327                  */
  328                 if ((lock->lf_flags & F_FLOCK) &&
  329                     lock->lf_type == F_WRLCK) {
  330                         lock->lf_type = F_UNLCK;
  331                         (void) lf_clearlock(lock, NULL);
  332                         lock->lf_type = F_WRLCK;
  333                 }
  334                 /*
  335                  * Add our lock to the blocked list and sleep until we're free.
  336                  * Remember who blocked us (for deadlock detection).
  337                  */
  338                 lock->lf_next = block;
  339                 TAILQ_INSERT_TAIL(&block->lf_blkhd, lock, lf_block);
  340 #ifdef LOCKF_DEBUG
  341                 if (lockf_debug & 1) {
  342                         lf_print("lf_setlock: blocking on", block);
  343                         lf_printlist("lf_setlock", block);
  344                 }
  345 #endif /* LOCKF_DEBUG */
  346                 error = ltsleep(lock, priority, lockstr, 0, interlock);
  347 
  348                 /*
  349                  * We may have been awakened by a signal (in
  350                  * which case we must remove ourselves from the
  351                  * blocked list) and/or by another process
  352                  * releasing a lock (in which case we have already
  353                  * been removed from the blocked list and our
  354                  * lf_next field set to NOLOCKF).
  355                  */
  356                 if (lock->lf_next != NOLOCKF) {
  357                         TAILQ_REMOVE(&lock->lf_next->lf_blkhd, lock, lf_block);
  358                         lock->lf_next = NOLOCKF;
  359                 }
  360                 if (error) {
  361                         free(lock, M_LOCKF);
  362                         return error;
  363                 }
  364         }
  365         /*
  366          * No blocks!!  Add the lock.  Note that we will
  367          * downgrade or upgrade any overlapping locks this
  368          * process already owns.
  369          *
  370          * Skip over locks owned by other processes.
  371          * Handle any locks that overlap and are owned by ourselves.
  372          */
  373         lock->lf_lwp = 0;
  374         prev = head;
  375         block = *head;
  376         needtolink = 1;
  377         for (;;) {
  378                 ovcase = lf_findoverlap(block, lock, SELF, &prev, &overlap);
  379                 if (ovcase)
  380                         block = overlap->lf_next;
  381                 /*
  382                  * Six cases:
  383                  *      0) no overlap
  384                  *      1) overlap == lock
  385                  *      2) overlap contains lock
  386                  *      3) lock contains overlap
  387                  *      4) overlap starts before lock
  388                  *      5) overlap ends after lock
  389                  */
  390                 switch (ovcase) {
  391                 case 0: /* no overlap */
  392                         if (needtolink) {
  393                                 *prev = lock;
  394                                 lock->lf_next = overlap;
  395                         }
  396                         break;
  397 
  398                 case 1: /* overlap == lock */
  399                         /*
  400                          * If downgrading lock, others may be
  401                          * able to acquire it.
  402                          */
  403                         if (lock->lf_type == F_RDLCK &&
  404                             overlap->lf_type == F_WRLCK)
  405                                 lf_wakelock(overlap);
  406                         overlap->lf_type = lock->lf_type;
  407                         FREE(lock, M_LOCKF);
  408                         lock = overlap; /* for debug output below */
  409                         break;
  410 
  411                 case 2: /* overlap contains lock */
  412                         /*
  413                          * Check for common starting point and different types.
  414                          */
  415                         if (overlap->lf_type == lock->lf_type) {
  416                                 free(lock, M_LOCKF);
  417                                 lock = overlap; /* for debug output below */
  418                                 break;
  419                         }
  420                         if (overlap->lf_start == lock->lf_start) {
  421                                 *prev = lock;
  422                                 lock->lf_next = overlap;
  423                                 overlap->lf_start = lock->lf_end + 1;
  424                         } else
  425                                 lf_split(overlap, lock, sparelock);
  426                         lf_wakelock(overlap);
  427                         break;
  428 
  429                 case 3: /* lock contains overlap */
  430                         /*
  431                          * If downgrading lock, others may be able to
  432                          * acquire it, otherwise take the list.
  433                          */
  434                         if (lock->lf_type == F_RDLCK &&
  435                             overlap->lf_type == F_WRLCK) {
  436                                 lf_wakelock(overlap);
  437                         } else {
  438                                 while ((ltmp = TAILQ_FIRST(&overlap->lf_blkhd))) {
  439                                         KASSERT(ltmp->lf_next == overlap);
  440                                         TAILQ_REMOVE(&overlap->lf_blkhd, ltmp,
  441                                             lf_block);
  442                                         ltmp->lf_next = lock;
  443                                         TAILQ_INSERT_TAIL(&lock->lf_blkhd,
  444                                             ltmp, lf_block);
  445                                 }
  446                         }
  447                         /*
  448                          * Add the new lock if necessary and delete the overlap.
  449                          */
  450                         if (needtolink) {
  451                                 *prev = lock;
  452                                 lock->lf_next = overlap->lf_next;
  453                                 prev = &lock->lf_next;
  454                                 needtolink = 0;
  455                         } else
  456                                 *prev = overlap->lf_next;
  457                         free(overlap, M_LOCKF);
  458                         continue;
  459 
  460                 case 4: /* overlap starts before lock */
  461                         /*
  462                          * Add lock after overlap on the list.
  463                          */
  464                         lock->lf_next = overlap->lf_next;
  465                         overlap->lf_next = lock;
  466                         overlap->lf_end = lock->lf_start - 1;
  467                         prev = &lock->lf_next;
  468                         lf_wakelock(overlap);
  469                         needtolink = 0;
  470                         continue;
  471 
  472                 case 5: /* overlap ends after lock */
  473                         /*
  474                          * Add the new lock before overlap.
  475                          */
  476                         if (needtolink) {
  477                                 *prev = lock;
  478                                 lock->lf_next = overlap;
  479                         }
  480                         overlap->lf_start = lock->lf_end + 1;
  481                         lf_wakelock(overlap);
  482                         break;
  483                 }
  484                 break;
  485         }
  486 #ifdef LOCKF_DEBUG
  487         if (lockf_debug & 1) {
  488                 lf_print("lf_setlock: got the lock", lock);
  489                 lf_printlist("lf_setlock", lock);
  490         }
  491 #endif /* LOCKF_DEBUG */
  492         return 0;
  493 }
  494 
  495 /*
  496  * Remove a byte-range lock on an inode.
  497  *
  498  * Generally, find the lock (or an overlap to that lock)
  499  * and remove it (or shrink it), then wakeup anyone we can.
  500  */
  501 static int
  502 lf_clearlock(struct lockf *unlock, struct lockf **sparelock)
  503 {
  504         struct lockf **head = unlock->lf_head;
  505         struct lockf *lf = *head;
  506         struct lockf *overlap, **prev;
  507         int ovcase;
  508 
  509         if (lf == NOLOCKF)
  510                 return 0;
  511 #ifdef LOCKF_DEBUG
  512         if (unlock->lf_type != F_UNLCK)
  513                 panic("lf_clearlock: bad type");
  514         if (lockf_debug & 1)
  515                 lf_print("lf_clearlock", unlock);
  516 #endif /* LOCKF_DEBUG */
  517         prev = head;
  518         while ((ovcase = lf_findoverlap(lf, unlock, SELF,
  519                                         &prev, &overlap)) != 0) {
  520                 /*
  521                  * Wakeup the list of locks to be retried.
  522                  */
  523                 lf_wakelock(overlap);
  524 
  525                 switch (ovcase) {
  526 
  527                 case 1: /* overlap == lock */
  528                         *prev = overlap->lf_next;
  529                         FREE(overlap, M_LOCKF);
  530                         break;
  531 
  532                 case 2: /* overlap contains lock: split it */
  533                         if (overlap->lf_start == unlock->lf_start) {
  534                                 overlap->lf_start = unlock->lf_end + 1;
  535                                 break;
  536                         }
  537                         lf_split(overlap, unlock, sparelock);
  538                         overlap->lf_next = unlock->lf_next;
  539                         break;
  540 
  541                 case 3: /* lock contains overlap */
  542                         *prev = overlap->lf_next;
  543                         lf = overlap->lf_next;
  544                         free(overlap, M_LOCKF);
  545                         continue;
  546 
  547                 case 4: /* overlap starts before lock */
  548                         overlap->lf_end = unlock->lf_start - 1;
  549                         prev = &overlap->lf_next;
  550                         lf = overlap->lf_next;
  551                         continue;
  552 
  553                 case 5: /* overlap ends after lock */
  554                         overlap->lf_start = unlock->lf_end + 1;
  555                         break;
  556                 }
  557                 break;
  558         }
  559 #ifdef LOCKF_DEBUG
  560         if (lockf_debug & 1)
  561                 lf_printlist("lf_clearlock", unlock);
  562 #endif /* LOCKF_DEBUG */
  563         return 0;
  564 }
  565 
  566 /*
  567  * Check whether there is a blocking lock,
  568  * and if so return its process identifier.
  569  */
  570 static int
  571 lf_getlock(struct lockf *lock, struct flock *fl)
  572 {
  573         struct lockf *block;
  574 
  575 #ifdef LOCKF_DEBUG
  576         if (lockf_debug & 1)
  577                 lf_print("lf_getlock", lock);
  578 #endif /* LOCKF_DEBUG */
  579 
  580         if ((block = lf_getblock(lock)) != NULL) {
  581                 fl->l_type = block->lf_type;
  582                 fl->l_whence = SEEK_SET;
  583                 fl->l_start = block->lf_start;
  584                 if (block->lf_end == -1)
  585                         fl->l_len = 0;
  586                 else
  587                         fl->l_len = block->lf_end - block->lf_start + 1;
  588                 if (block->lf_flags & F_POSIX)
  589                         fl->l_pid = ((struct proc *)block->lf_id)->p_pid;
  590                 else
  591                         fl->l_pid = -1;
  592         } else {
  593                 fl->l_type = F_UNLCK;
  594         }
  595         return 0;
  596 }
  597 
  598 /*
  599  * Walk the list of locks for an inode and
  600  * return the first blocking lock.
  601  */
  602 static struct lockf *
  603 lf_getblock(struct lockf *lock)
  604 {
  605         struct lockf **prev, *overlap, *lf = *(lock->lf_head);
  606 
  607         prev = lock->lf_head;
  608         while (lf_findoverlap(lf, lock, OTHERS, &prev, &overlap) != 0) {
  609                 /*
  610                  * We've found an overlap, see if it blocks us
  611                  */
  612                 if ((lock->lf_type == F_WRLCK || overlap->lf_type == F_WRLCK))
  613                         return overlap;
  614                 /*
  615                  * Nope, point to the next one on the list and
  616                  * see if it blocks us
  617                  */
  618                 lf = overlap->lf_next;
  619         }
  620         return NOLOCKF;
  621 }
  622 
  623 /*
  624  * Walk the list of locks for an inode to
  625  * find an overlapping lock (if any).
  626  *
  627  * NOTE: this returns only the FIRST overlapping lock.  There
  628  *       may be more than one.
  629  */
  630 static int
  631 lf_findoverlap(struct lockf *lf, struct lockf *lock, int type,
  632     struct lockf ***prev, struct lockf **overlap)
  633 {
  634         off_t start, end;
  635 
  636         *overlap = lf;
  637         if (lf == NOLOCKF)
  638                 return 0;
  639 #ifdef LOCKF_DEBUG
  640         if (lockf_debug & 2)
  641                 lf_print("lf_findoverlap: looking for overlap in", lock);
  642 #endif /* LOCKF_DEBUG */
  643         start = lock->lf_start;
  644         end = lock->lf_end;
  645         while (lf != NOLOCKF) {
  646                 if (((type == SELF) && lf->lf_id != lock->lf_id) ||
  647                     ((type == OTHERS) && lf->lf_id == lock->lf_id)) {
  648                         *prev = &lf->lf_next;
  649                         *overlap = lf = lf->lf_next;
  650                         continue;
  651                 }
  652 #ifdef LOCKF_DEBUG
  653                 if (lockf_debug & 2)
  654                         lf_print("\tchecking", lf);
  655 #endif /* LOCKF_DEBUG */
  656                 /*
  657                  * OK, check for overlap
  658                  *
  659                  * Six cases:
  660                  *      0) no overlap
  661                  *      1) overlap == lock
  662                  *      2) overlap contains lock
  663                  *      3) lock contains overlap
  664                  *      4) overlap starts before lock
  665                  *      5) overlap ends after lock
  666                  */
  667                 if ((lf->lf_end != -1 && start > lf->lf_end) ||
  668                     (end != -1 && lf->lf_start > end)) {
  669                         /* Case 0 */
  670 #ifdef LOCKF_DEBUG
  671                         if (lockf_debug & 2)
  672                                 printf("no overlap\n");
  673 #endif /* LOCKF_DEBUG */
  674                         if ((type & SELF) && end != -1 && lf->lf_start > end)
  675                                 return 0;
  676                         *prev = &lf->lf_next;
  677                         *overlap = lf = lf->lf_next;
  678                         continue;
  679                 }
  680                 if ((lf->lf_start == start) && (lf->lf_end == end)) {
  681                         /* Case 1 */
  682 #ifdef LOCKF_DEBUG
  683                         if (lockf_debug & 2)
  684                                 printf("overlap == lock\n");
  685 #endif /* LOCKF_DEBUG */
  686                         return 1;
  687                 }
  688                 if ((lf->lf_start <= start) &&
  689                     (end != -1) &&
  690                     ((lf->lf_end >= end) || (lf->lf_end == -1))) {
  691                         /* Case 2 */
  692 #ifdef LOCKF_DEBUG
  693                         if (lockf_debug & 2)
  694                                 printf("overlap contains lock\n");
  695 #endif /* LOCKF_DEBUG */
  696                         return 2;
  697                 }
  698                 if (start <= lf->lf_start &&
  699                            (end == -1 ||
  700                            (lf->lf_end != -1 && end >= lf->lf_end))) {
  701                         /* Case 3 */
  702 #ifdef LOCKF_DEBUG
  703                         if (lockf_debug & 2)
  704                                 printf("lock contains overlap\n");
  705 #endif /* LOCKF_DEBUG */
  706                         return 3;
  707                 }
  708                 if ((lf->lf_start < start) &&
  709                         ((lf->lf_end >= start) || (lf->lf_end == -1))) {
  710                         /* Case 4 */
  711 #ifdef LOCKF_DEBUG
  712                         if (lockf_debug & 2)
  713                                 printf("overlap starts before lock\n");
  714 #endif /* LOCKF_DEBUG */
  715                         return 4;
  716                 }
  717                 if ((lf->lf_start > start) &&
  718                         (end != -1) &&
  719                         ((lf->lf_end > end) || (lf->lf_end == -1))) {
  720                         /* Case 5 */
  721 #ifdef LOCKF_DEBUG
  722                         if (lockf_debug & 2)
  723                                 printf("overlap ends after lock\n");
  724 #endif /* LOCKF_DEBUG */
  725                         return 5;
  726                 }
  727                 panic("lf_findoverlap: default");
  728         }
  729         return 0;
  730 }
  731 
  732 /*
  733  * Split a lock and a contained region into
  734  * two or three locks as necessary.
  735  */
  736 static void
  737 lf_split(struct lockf *lock1, struct lockf *lock2, struct lockf **sparelock)
  738 {
  739         struct lockf *splitlock;
  740 
  741 #ifdef LOCKF_DEBUG
  742         if (lockf_debug & 2) {
  743                 lf_print("lf_split", lock1);
  744                 lf_print("splitting from", lock2);
  745         }
  746 #endif /* LOCKF_DEBUG */
  747         /*
  748          * Check to see if spliting into only two pieces.
  749          */
  750         if (lock1->lf_start == lock2->lf_start) {
  751                 lock1->lf_start = lock2->lf_end + 1;
  752                 lock2->lf_next = lock1;
  753                 return;
  754         }
  755         if (lock1->lf_end == lock2->lf_end) {
  756                 lock1->lf_end = lock2->lf_start - 1;
  757                 lock2->lf_next = lock1->lf_next;
  758                 lock1->lf_next = lock2;
  759                 return;
  760         }
  761         /*
  762          * Make a new lock consisting of the last part of
  763          * the encompassing lock
  764          */
  765         splitlock = *sparelock;
  766         *sparelock = NULL;
  767         memcpy(splitlock, lock1, sizeof(*splitlock));
  768         splitlock->lf_start = lock2->lf_end + 1;
  769         TAILQ_INIT(&splitlock->lf_blkhd);
  770         lock1->lf_end = lock2->lf_start - 1;
  771         /*
  772          * OK, now link it in
  773          */
  774         splitlock->lf_next = lock1->lf_next;
  775         lock2->lf_next = splitlock;
  776         lock1->lf_next = lock2;
  777 }
  778 
  779 /*
  780  * Wakeup a blocklist
  781  */
  782 static void
  783 lf_wakelock(struct lockf *listhead)
  784 {
  785         struct lockf *wakelock;
  786 
  787         while ((wakelock = TAILQ_FIRST(&listhead->lf_blkhd))) {
  788                 KASSERT(wakelock->lf_next == listhead);
  789                 TAILQ_REMOVE(&listhead->lf_blkhd, wakelock, lf_block);
  790                 wakelock->lf_next = NOLOCKF;
  791 #ifdef LOCKF_DEBUG
  792                 if (lockf_debug & 2)
  793                         lf_print("lf_wakelock: awakening", wakelock);
  794 #endif
  795                 wakeup(wakelock);
  796         }
  797 }
  798 
  799 #ifdef LOCKF_DEBUG
  800 /*
  801  * Print out a lock.
  802  */
  803 static void
  804 lf_print(char *tag, struct lockf *lock)
  805 {
  806         
  807         printf("%s: lock %p for ", tag, lock);
  808         if (lock->lf_flags & F_POSIX)
  809                 printf("proc %d", ((struct proc *)lock->lf_id)->p_pid);
  810         else
  811                 printf("file 0x%p", (struct file *)lock->lf_id);
  812         printf(" %s, start %qx, end %qx",
  813                 lock->lf_type == F_RDLCK ? "shared" :
  814                 lock->lf_type == F_WRLCK ? "exclusive" :
  815                 lock->lf_type == F_UNLCK ? "unlock" :
  816                 "unknown", lock->lf_start, lock->lf_end);
  817         if (TAILQ_FIRST(&lock->lf_blkhd))
  818                 printf(" block %p\n", TAILQ_FIRST(&lock->lf_blkhd));
  819         else
  820                 printf("\n");
  821 }
  822 
  823 static void
  824 lf_printlist(char *tag, struct lockf *lock)
  825 {
  826         struct lockf *lf, *blk;
  827 
  828         printf("%s: Lock list:\n", tag);
  829         for (lf = *lock->lf_head; lf; lf = lf->lf_next) {
  830                 printf("\tlock %p for ", lf);
  831                 if (lf->lf_flags & F_POSIX)
  832                         printf("proc %d", ((struct proc *)lf->lf_id)->p_pid);
  833                 else
  834                         printf("file 0x%p", (struct file *)lf->lf_id);
  835                 printf(", %s, start %qx, end %qx",
  836                         lf->lf_type == F_RDLCK ? "shared" :
  837                         lf->lf_type == F_WRLCK ? "exclusive" :
  838                         lf->lf_type == F_UNLCK ? "unlock" :
  839                         "unknown", lf->lf_start, lf->lf_end);
  840                 TAILQ_FOREACH(blk, &lf->lf_blkhd, lf_block) {
  841                         if (blk->lf_flags & F_POSIX)
  842                                 printf("proc %d",
  843                                     ((struct proc *)blk->lf_id)->p_pid);
  844                         else
  845                                 printf("file 0x%p", (struct file *)blk->lf_id);
  846                         printf(", %s, start %qx, end %qx",
  847                                 blk->lf_type == F_RDLCK ? "shared" :
  848                                 blk->lf_type == F_WRLCK ? "exclusive" :
  849                                 blk->lf_type == F_UNLCK ? "unlock" :
  850                                 "unknown", blk->lf_start, blk->lf_end);
  851                         if (TAILQ_FIRST(&blk->lf_blkhd))
  852                                  panic("lf_printlist: bad list");
  853                 }
  854                 printf("\n");
  855         }
  856 }
  857 #endif /* LOCKF_DEBUG */

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