lockinit, lockdestroy, lockcount, lockmgr, lockstatus, lockmgr_printinfo
-- lockmgr family of functions
lockinit(struct lock *lkp, int prio, const char *wmesg, int timo,
lockdestroy(struct lock *lkp);
lockcount(struct lock *lkp);
lockmgr(struct lock *lkp, u_int flags, struct mtx *interlkp,
struct thread *td);
lockstatus(struct lock *lkp, struct thread *td);
lockmgr_printinfo(struct lock *lkp);
The lockinit() function is used to initialize a lock. It must be called
before any operation can be performed on a lock. Its arguments are:
lkp A pointer to the lock to initialize.
prio The priority passed to msleep(9).
wmesg The lock message. This is used for both debugging output and
timo The timeout value passed to msleep(9).
flags The flags the lock is to be initialized with.
LK_NOWAIT Do not sleep while acquiring the lock.
LK_SLEEPFAIL Fail after a sleep.
LK_CANRECURSE Allow recursive exclusive locks.
LK_REENABLE Re-enable the lock after a drain.
LK_NOPAUSE Disable the spinlock while acquiring the lock.
LK_TIMELOCK Use timo during a sleep; otherwise, 0 is used.
The lockdestroy() function is used to destroy a lock, and while it is
called in a number of places in the kernel, it currently does nothing.
The lockcount() function returns a count of the number of exclusive locks
and shared locks held against the lock lkp.
The lockmgr() function handles general locking functionality within the
kernel, including support for shared and exclusive locks, and recursion.
lockmgr() is also able to upgrade and downgrade locks.
Its arguments are:
lkp A pointer to the lock to manipulate.
flags Flags indicating what action is to be taken.
LK_SHARED Acquire a shared lock. If an exclusive lock is
currently held, it will be downgraded.
LK_EXCLUSIVE Acquire an exclusive lock. If an exclusive
lock is already held, and LK_CANRECURSE is not
set, the system will panic(9).
LK_DOWNGRADE Downgrade exclusive lock to a shared lock.
Downgrading a shared lock is not permitted. If
an exclusive lock has been recursed, all references
will be downgraded.
LK_EXCLUPGRADE Upgrade a shared lock to an exclusive lock.
Fails with EBUSY if there is someone ahead of
you in line waiting for an upgrade. If this
call fails, the shared lock is lost. Attempts
to upgrade an exclusive lock will cause a
LK_UPGRADE Upgrade a shared lock to an exclusive lock. If
this call fails, the shared lock is lost.
Attempts to upgrade an exclusive lock will
cause a panic(9).
LK_RELEASE Release the lock. Releasing a lock that is not
held can cause a panic(9).
LK_DRAIN Wait for all activity on the lock to end, then
mark it decommissioned. This is used before
freeing a lock that is part of a piece of memory
that is about to be freed. (As documented
LK_SLEEPFAIL Fail if operation has slept.
LK_NOWAIT Do not allow the call to sleep. This can be
used to test the lock.
LK_CANRECURSE Allow recursion on an exclusive lock. For
every lock there must be a release.
LK_INTERLOCK Unlock the interlock (which should be locked
interlkp An interlock mutex for controlling group access to the lock.
If LK_INTERLOCK is specified, lockmgr() assumes interlkp is
currently owned and not recursed, and will return it unlocked.
td A thread responsible for this call. NULL becomes LK_KERNPROC.
The lockstatus() function returns the status of the lock in relation to
the thread passed to it. Note that if td is NULL and an exclusive lock
is held, LK_EXCLUSIVE will be returned.
The lockmgr_printinfo() function prints debugging information about the
lock. It is used primarily by VOP_PRINT(9) functions.
The lockcount() function returns an integer greater than or equal to
The lockmgr() function returns 0 on success and non-zero on failure.
The lockstatus() function returns:
LK_EXCLUSIVE An exclusive lock is held by the thread td.
LK_EXCLOTHER An exclusive lock is held by someone other than the thread
LK_SHARED A shared lock is held.
0 The lock is not held by anyone.
lockmgr() fails if:
[EBUSY] LK_FORCEUPGRADE was requested and another thread had
already requested a lock upgrade.
[EBUSY] LK_NOWAIT was set, and a sleep would have been
[ENOLCK] LK_SLEEPFAIL was set and lockmgr() did sleep.
[EINTR] PCATCH was set in the lock priority, and a signal was
delivered during a sleep. Note the ERESTART error
[ERESTART] PCATCH was set in the lock priority, a signal was
delivered during a sleep, and the system call is to be
[EWOULDBLOCK] a non-zero timeout was given, and the timeout expired.
If LK_INTERLOCK is passed in the flags argument to lockmgr(), the
interlkp must be held prior to calling lockmgr(), and will be returned
Upgrade attempts that fail result in the loss of the lock that is currently
held. Also, it is invalid to upgrade an exclusive lock, and a
panic(9) will be the result of trying.
msleep(9), mtx_assert(9), panic(9), VOP_PRINT(9)
This man page was written by Chad David <firstname.lastname@example.org>.
FreeBSD 5.2.1 July 9, 2001 FreeBSD 5.2.1 [ Back ]