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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.
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33 * @(#)lock.h 8.12 (Berkeley) 5/19/95
37 #ifndef _SYS_LOCKMGR_H_
38 #define _SYS_LOCKMGR_H_
41 #include <sys/stack.h> /* XXX */
47 * The general lock structure. Provides for multiple shared locks,
48 * upgrading from shared to exclusive, and sleeping until the 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 */
63 struct stack lk_stack;
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
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
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.
99 * These are flags that are passed to the lockmgr routine.
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 */
111 * External lock flags.
113 * These may be set in lock_init to set their mode permanently,
114 * or passed in as arguments to the lock manager.
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 */
123 * Nonpersistent external flags.
125 #define LK_RETRY 0x00001000 /* vn_lock: retry until locked */
126 #define LK_INTERLOCK 0x00002000 /*
127 * unlock passed mutex after getting
131 * Internal lock flags.
133 * These flags are used internally to the lock manager.
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 */
142 * Internal state flags corresponding to lk_sharecount, and lk_waitcount
144 #define LK_SHARE_NONZERO 0x01000000
145 #define LK_WAIT_NONZERO 0x02000000
149 * Lock return status.
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).
166 * Indicator that no process holds exclusive lock
168 #define LK_KERNPROC ((struct thread *)-2)
169 #define LK_NOPROC ((struct thread *) -1)
172 #define LOCKMGR_ASSERT(lkp, what, p) do { \
175 if (lockstatus((lkp), (p)) == LK_SHARED) \
177 /* fall into exclusive */ \
179 if (lockstatus((lkp), (p)) != LK_EXCLUSIVE) \
180 panic("lock %s %s not held at %s:%d", \
181 (lkp)->lk_wmesg, #what, __FILE__, \
185 panic("unknown LOCKMGR_ASSERT at %s:%d", __FILE__, \
189 #else /* INVARIANTS */
190 #define LOCKMGR_ASSERT(lkp, p, what)
191 #endif /* INVARIANTS */
193 void dumplockinfo(struct lock *lkp);
196 void lockinit(struct lock *, int prio, const char *wmesg,
197 int timo, int flags);
198 void lockdestroy(struct lock *);
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 int lockwaiters(struct lock *);
208 int lockmgr_chain(struct thread *td, struct thread **ownerp);
211 #endif /* !_SYS_LOCKMGR_H_ */