The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/sys/lockmgr.h

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    1 /*-
    2  * Copyright (c) 1995
    3  *      The Regents of the University of California.  All rights reserved.
    4  *
    5  * This code contains ideas from software contributed to Berkeley by
    6  * Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating
    7  * System project at Carnegie-Mellon University.
    8  *
    9  * Redistribution and use in source and binary forms, with or without
   10  * modification, are permitted provided that the following conditions
   11  * are met:
   12  * 1. Redistributions of source code must retain the above copyright
   13  *    notice, this list of conditions and the following disclaimer.
   14  * 2. Redistributions in binary form must reproduce the above copyright
   15  *    notice, this list of conditions and the following disclaimer in the
   16  *    documentation and/or other materials provided with the distribution.
   17  * 4. Neither the name of the University nor the names of its contributors
   18  *    may be used to endorse or promote products derived from this software
   19  *    without specific prior written permission.
   20  *
   21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   31  * SUCH DAMAGE.
   32  *
   33  *      @(#)lock.h      8.12 (Berkeley) 5/19/95
   34  * $FreeBSD: releng/7.3/sys/sys/lockmgr.h 178777 2008-05-05 15:58:44Z attilio $
   35  */
   36 
   37 #ifndef _SYS_LOCKMGR_H_
   38 #define _SYS_LOCKMGR_H_
   39 
   40 #ifdef  DEBUG_LOCKS
   41 #include <sys/stack.h> /* XXX */
   42 #endif
   43 #include <sys/queue.h>
   44 #include <sys/_lock.h>
   45 
   46 struct  mtx;
   47 
   48 /*
   49  * The general lock structure.  Provides for multiple shared locks,
   50  * upgrading from shared to exclusive, and sleeping until the lock
   51  * can be gained.
   52  */
   53 struct lock {
   54         struct lock_object lk_object;   /* common lock properties */
   55         struct  mtx *lk_interlock;      /* lock on remaining fields */
   56         u_int   lk_flags;               /* see below */
   57         int     lk_sharecount;          /* # of accepted shared locks */
   58         int     lk_waitcount;           /* # of processes sleeping for lock */
   59         short   lk_exclusivecount;      /* # of recursive exclusive locks */
   60         short   lk_prio;                /* priority at which to sleep */
   61         int     lk_timo;                /* maximum sleep time (for tsleep) */
   62         struct thread *lk_lockholder;   /* thread of exclusive lock holder */
   63         struct  lock *lk_newlock;       /* lock taking over this lock */
   64 
   65 #ifdef  DEBUG_LOCKS
   66         struct stack lk_stack;
   67 #endif
   68 };
   69 
   70 #define lk_wmesg lk_object.lo_name
   71 /*
   72  * Lock request types:
   73  *   LK_SHARED - get one of many possible shared locks. If a process
   74  *      holding an exclusive lock requests a shared lock, the exclusive
   75  *      lock(s) will be downgraded to shared locks.
   76  *   LK_EXCLUSIVE - stop further shared locks, when they are cleared,
   77  *      grant a pending upgrade if it exists, then grant an exclusive
   78  *      lock. Only one exclusive lock may exist at a time, except that
   79  *      a process holding an exclusive lock may get additional exclusive
   80  *      locks if it explicitly sets the LK_CANRECURSE flag in the lock
   81  *      request, or if the LK_CANRECUSE flag was set when the lock was
   82  *      initialized.
   83  *   LK_UPGRADE - the process must hold a shared lock that it wants to
   84  *      have upgraded to an exclusive lock. Other processes may get
   85  *      exclusive access to the resource between the time that the upgrade
   86  *      is requested and the time that it is granted.
   87  *   LK_EXCLUPGRADE - the process must hold a shared lock that it wants to
   88  *      have upgraded to an exclusive lock. If the request succeeds, no
   89  *      other processes will have gotten exclusive access to the resource
   90  *      between the time that the upgrade is requested and the time that
   91  *      it is granted. However, if another process has already requested
   92  *      an upgrade, the request will fail (see error returns below).
   93  *   LK_DOWNGRADE - the process must hold an exclusive lock that it wants
   94  *      to have downgraded to a shared lock. If the process holds multiple
   95  *      (recursive) exclusive locks, they will all be downgraded to shared
   96  *      locks.
   97  *   LK_RELEASE - release one instance of a lock.
   98  *   LK_DRAIN - wait for all activity on the lock to end, then mark it
   99  *      decommissioned. This feature is used before freeing a lock that
  100  *      is part of a piece of memory that is about to be freed.
  101  *   LK_EXCLOTHER - return for lockstatus().  Used when another process
  102  *      holds the lock exclusively.
  103  *
  104  * These are flags that are passed to the lockmgr routine.
  105  */
  106 #define LK_TYPE_MASK    0x0000000f      /* type of lock sought */
  107 #define LK_SHARED       0x00000001      /* shared lock */
  108 #define LK_EXCLUSIVE    0x00000002      /* exclusive lock */
  109 #define LK_UPGRADE      0x00000003      /* shared-to-exclusive upgrade */
  110 #define LK_EXCLUPGRADE  0x00000004      /* first shared-to-exclusive upgrade */
  111 #define LK_DOWNGRADE    0x00000005      /* exclusive-to-shared downgrade */
  112 #define LK_RELEASE      0x00000006      /* release any type of lock */
  113 #define LK_DRAIN        0x00000007      /* wait for all lock activity to end */
  114 #define LK_EXCLOTHER    0x00000008      /* other process holds lock */
  115 /*
  116  * External lock flags.
  117  *
  118  * These may be set in lock_init to set their mode permanently,
  119  * or passed in as arguments to the lock manager.
  120  */
  121 #define LK_EXTFLG_MASK  0x00000ff0      /* mask of external flags */
  122 #define LK_NOWAIT       0x00000010      /* do not sleep to await lock */
  123 #define LK_SLEEPFAIL    0x00000020      /* sleep, then return failure */
  124 #define LK_CANRECURSE   0x00000040      /* allow recursive exclusive lock */
  125 #define LK_NOSHARE      0x00000080      /* Only allow exclusive locks */
  126 #define LK_TIMELOCK     0x00000100      /* use lk_timo, else no timeout */
  127 /*
  128  * Nonpersistent external flags.
  129  */
  130 #define LK_RETRY        0x00001000 /* vn_lock: retry until locked */
  131 #define LK_INTERLOCK    0x00002000 /*
  132                                     * unlock passed mutex after getting
  133                                     * lk_interlock
  134                                     */
  135 /*
  136  * Internal lock flags.
  137  *
  138  * These flags are used internally to the lock manager.
  139  */
  140 #define LK_WANT_UPGRADE 0x00010000      /* waiting for share-to-excl upgrade */
  141 #define LK_WANT_EXCL    0x00020000      /* exclusive lock sought */
  142 #define LK_HAVE_EXCL    0x00040000      /* exclusive lock obtained */
  143 #define LK_WAITDRAIN    0x00080000      /* process waiting for lock to drain */
  144 #define LK_DRAINING     0x00100000      /* lock is being drained */
  145 #define LK_INTERNAL     0x00200000/* The internal lock is already held */
  146 /*
  147  * Internal state flags corresponding to lk_sharecount, and lk_waitcount
  148  */
  149 #define LK_SHARE_NONZERO 0x01000000
  150 #define LK_WAIT_NONZERO  0x02000000
  151 
  152 
  153 /*
  154  * Lock return status.
  155  *
  156  * Successfully obtained locks return 0. Locks will always succeed
  157  * unless one of the following is true:
  158  *      LK_FORCEUPGRADE is requested and some other process has already
  159  *          requested a lock upgrade (returns EBUSY).
  160  *      LK_WAIT is set and a sleep would be required (returns EBUSY).
  161  *      LK_SLEEPFAIL is set and a sleep was done (returns ENOLCK).
  162  *      PCATCH is set in lock priority and a signal arrives (returns
  163  *          either EINTR or ERESTART if system calls is to be restarted).
  164  *      Non-null lock timeout and timeout expires (returns EWOULDBLOCK).
  165  * A failed lock attempt always returns a non-zero error value. No lock
  166  * is held after an error return (in particular, a failed LK_UPGRADE
  167  * or LK_FORCEUPGRADE will have released its shared access lock).
  168  */
  169 
  170 /*
  171  * Indicator that no process holds exclusive lock
  172  */
  173 #define LK_KERNPROC ((struct thread *)-2)
  174 #define LK_NOPROC ((struct thread *) -1)
  175 
  176 #ifdef _KERNEL
  177 
  178 #if !defined(LOCK_FILE) || !defined(LOCK_LINE)
  179 #error  "LOCK_FILE and LOCK_LINE not defined, include <sys/lock.h> before"
  180 #endif
  181 
  182 #ifdef INVARIANTS
  183 #define LOCKMGR_ASSERT(lkp, what, p) do {                               \
  184         switch ((what)) {                                               \
  185         case LK_SHARED:                                                 \
  186                 if (lockstatus((lkp), (p)) == LK_SHARED)                \
  187                         break;                                          \
  188                 /* fall into exclusive */                               \
  189         case LK_EXCLUSIVE:                                              \
  190                 if (lockstatus((lkp), (p)) != LK_EXCLUSIVE)             \
  191                         panic("lock %s %s not held at %s:%d",           \
  192                             (lkp)->lk_wmesg, #what, LOCK_FILE,          \
  193                             LOCK_LINE);                                 \
  194                 break;                                                  \
  195         default:                                                        \
  196                 panic("unknown LOCKMGR_ASSERT at %s:%d", LOCK_FILE,     \
  197                     LOCK_LINE);                                         \
  198         }                                                               \
  199 } while (0)
  200 #else   /* INVARIANTS */
  201 #define LOCKMGR_ASSERT(lkp, p, what)
  202 #endif  /* INVARIANTS */
  203 
  204 struct thread;
  205 
  206 void    lockinit(struct lock *, int prio, const char *wmesg,
  207                         int timo, int flags);
  208 void    lockdestroy(struct lock *);
  209 
  210 int     _lockmgr(struct lock *, u_int flags,
  211                  struct mtx *, struct thread *p, char *file, int line);
  212 void    transferlockers(struct lock *, struct lock *);
  213 void    lockmgr_printinfo(struct lock *);
  214 int     lockstatus(struct lock *, struct thread *);
  215 int     lockcount(struct lock *);
  216 int     lockwaiters(struct lock *);
  217 
  218 #define lockmgr(lock, flags, mtx, td)                                   \
  219         _lockmgr((lock), (flags), (mtx), (td), LOCK_FILE, LOCK_LINE)
  220 #ifdef DDB
  221 int     lockmgr_chain(struct thread *td, struct thread **ownerp);
  222 #endif
  223 
  224 #endif /* !_KERNEL */
  225 
  226 #endif /* !_SYS_LOCKMGR_H_ */

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