The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: 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/6.1/sys/sys/lockmgr.h 158179 2006-04-30 16:44:43Z cvs2svn $
   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 
   44 struct  mtx;
   45 
   46 /*
   47  * The general lock structure.  Provides for multiple shared locks,
   48  * upgrading from shared to exclusive, and sleeping until the lock
   49  * can be gained.
   50  */
   51 struct lock {
   52         struct  mtx *lk_interlock;      /* lock on remaining fields */
   53         u_int   lk_flags;               /* see below */
   54         int     lk_sharecount;          /* # of accepted shared locks */
   55         int     lk_waitcount;           /* # of processes sleeping for lock */
   56         short   lk_exclusivecount;      /* # of recursive exclusive locks */
   57         short   lk_prio;                /* priority at which to sleep */
   58         const char *lk_wmesg;           /* resource sleeping (for tsleep) */
   59         int     lk_timo;                /* maximum sleep time (for tsleep) */
   60         struct thread *lk_lockholder;   /* thread of exclusive lock holder */
   61         struct  lock *lk_newlock;       /* lock taking over this lock */
   62 #ifdef  DEBUG_LOCKS
   63         struct stack lk_stack;
   64 #endif
   65 };
   66 /*
   67  * Lock request types:
   68  *   LK_SHARED - get one of many possible shared locks. If a process
   69  *      holding an exclusive lock requests a shared lock, the exclusive
   70  *      lock(s) will be downgraded to shared locks.
   71  *   LK_EXCLUSIVE - stop further shared locks, when they are cleared,
   72  *      grant a pending upgrade if it exists, then grant an exclusive
   73  *      lock. Only one exclusive lock may exist at a time, except that
   74  *      a process holding an exclusive lock may get additional exclusive
   75  *      locks if it explicitly sets the LK_CANRECURSE flag in the lock
   76  *      request, or if the LK_CANRECUSE flag was set when the lock was
   77  *      initialized.
   78  *   LK_UPGRADE - the process must hold a shared lock that it wants to
   79  *      have upgraded to an exclusive lock. Other processes may get
   80  *      exclusive access to the resource between the time that the upgrade
   81  *      is requested and the time that it is granted.
   82  *   LK_EXCLUPGRADE - the process must hold a shared lock that it wants to
   83  *      have upgraded to an exclusive lock. If the request succeeds, no
   84  *      other processes will have gotten exclusive access to the resource
   85  *      between the time that the upgrade is requested and the time that
   86  *      it is granted. However, if another process has already requested
   87  *      an upgrade, the request will fail (see error returns below).
   88  *   LK_DOWNGRADE - the process must hold an exclusive lock that it wants
   89  *      to have downgraded to a shared lock. If the process holds multiple
   90  *      (recursive) exclusive locks, they will all be downgraded to shared
   91  *      locks.
   92  *   LK_RELEASE - release one instance of a lock.
   93  *   LK_DRAIN - wait for all activity on the lock to end, then mark it
   94  *      decommissioned. This feature is used before freeing a lock that
   95  *      is part of a piece of memory that is about to be freed.
   96  *   LK_EXCLOTHER - return for lockstatus().  Used when another process
   97  *      holds the lock exclusively.
   98  *
   99  * These are flags that are passed to the lockmgr routine.
  100  */
  101 #define LK_TYPE_MASK    0x0000000f      /* type of lock sought */
  102 #define LK_SHARED       0x00000001      /* shared lock */
  103 #define LK_EXCLUSIVE    0x00000002      /* exclusive lock */
  104 #define LK_UPGRADE      0x00000003      /* shared-to-exclusive upgrade */
  105 #define LK_EXCLUPGRADE  0x00000004      /* first shared-to-exclusive upgrade */
  106 #define LK_DOWNGRADE    0x00000005      /* exclusive-to-shared downgrade */
  107 #define LK_RELEASE      0x00000006      /* release any type of lock */
  108 #define LK_DRAIN        0x00000007      /* wait for all lock activity to end */
  109 #define LK_EXCLOTHER    0x00000008      /* other process holds lock */
  110 /*
  111  * External lock flags.
  112  *
  113  * These may be set in lock_init to set their mode permanently,
  114  * or passed in as arguments to the lock manager.
  115  */
  116 #define LK_EXTFLG_MASK  0x00000ff0      /* mask of external flags */
  117 #define LK_NOWAIT       0x00000010      /* do not sleep to await lock */
  118 #define LK_SLEEPFAIL    0x00000020      /* sleep, then return failure */
  119 #define LK_CANRECURSE   0x00000040      /* allow recursive exclusive lock */
  120 #define LK_NOSHARE      0x00000080      /* Only allow exclusive locks */
  121 #define LK_TIMELOCK     0x00000100      /* use lk_timo, else no timeout */
  122 /*
  123  * Nonpersistent external flags.
  124  */
  125 #define LK_RETRY        0x00001000 /* vn_lock: retry until locked */
  126 #define LK_INTERLOCK    0x00002000 /*
  127                                     * unlock passed mutex after getting
  128                                     * lk_interlock
  129                                     */
  130 /*
  131  * Internal lock flags.
  132  *
  133  * These flags are used internally to the lock manager.
  134  */
  135 #define LK_WANT_UPGRADE 0x00010000      /* waiting for share-to-excl upgrade */
  136 #define LK_WANT_EXCL    0x00020000      /* exclusive lock sought */
  137 #define LK_HAVE_EXCL    0x00040000      /* exclusive lock obtained */
  138 #define LK_WAITDRAIN    0x00080000      /* process waiting for lock to drain */
  139 #define LK_DRAINING     0x00100000      /* lock is being drained */
  140 #define LK_INTERNAL     0x00200000/* The internal lock is already held */
  141 /*
  142  * Internal state flags corresponding to lk_sharecount, and lk_waitcount
  143  */
  144 #define LK_SHARE_NONZERO 0x01000000
  145 #define LK_WAIT_NONZERO  0x02000000
  146 
  147 
  148 /*
  149  * Lock return status.
  150  *
  151  * Successfully obtained locks return 0. Locks will always succeed
  152  * unless one of the following is true:
  153  *      LK_FORCEUPGRADE is requested and some other process has already
  154  *          requested a lock upgrade (returns EBUSY).
  155  *      LK_WAIT is set and a sleep would be required (returns EBUSY).
  156  *      LK_SLEEPFAIL is set and a sleep was done (returns ENOLCK).
  157  *      PCATCH is set in lock priority and a signal arrives (returns
  158  *          either EINTR or ERESTART if system calls is to be restarted).
  159  *      Non-null lock timeout and timeout expires (returns EWOULDBLOCK).
  160  * A failed lock attempt always returns a non-zero error value. No lock
  161  * is held after an error return (in particular, a failed LK_UPGRADE
  162  * or LK_FORCEUPGRADE will have released its shared access lock).
  163  */
  164 
  165 /*
  166  * Indicator that no process holds exclusive lock
  167  */
  168 #define LK_KERNPROC ((struct thread *)-2)
  169 #define LK_NOPROC ((struct thread *) -1)
  170 
  171 #ifdef INVARIANTS
  172 #define LOCKMGR_ASSERT(lkp, what, p) do {                               \
  173         switch ((what)) {                                               \
  174         case LK_SHARED:                                                 \
  175                 if (lockstatus((lkp), (p)) == LK_SHARED)                \
  176                         break;                                          \
  177                 /* fall into exclusive */                               \
  178         case LK_EXCLUSIVE:                                              \
  179                 if (lockstatus((lkp), (p)) != LK_EXCLUSIVE)             \
  180                         panic("lock %s %s not held at %s:%d",           \
  181                             (lkp)->lk_wmesg, #what, __FILE__,           \
  182                             __LINE__);                                  \
  183                 break;                                                  \
  184         default:                                                        \
  185                 panic("unknown LOCKMGR_ASSERT at %s:%d", __FILE__,      \
  186                     __LINE__);                                          \
  187         }                                                               \
  188 } while (0)
  189 #else   /* INVARIANTS */
  190 #define LOCKMGR_ASSERT(lkp, p, what)
  191 #endif  /* INVARIANTS */
  192 
  193 void dumplockinfo(struct lock *lkp);
  194 struct thread;
  195 
  196 void    lockinit(struct lock *, int prio, const char *wmesg,
  197                         int timo, int flags);
  198 void    lockdestroy(struct lock *);
  199 
  200 int     lockmgr(struct lock *, u_int flags,
  201                         struct mtx *, struct thread *p);
  202 void    transferlockers(struct lock *, struct lock *);
  203 void    lockmgr_printinfo(struct lock *);
  204 int     lockstatus(struct lock *, struct thread *);
  205 int     lockcount(struct lock *);
  206 
  207 #endif /* !_SYS_LOCKMGR_H_ */

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