table of contents
|LOCK(9)||Kernel Developer's Manual||LOCK(9)|
NAME¶lockinit, lockdestroy, lockmgr, lockmgr_args, lockmgr_args_rw, lockmgr_disown, lockmgr_printinfo, lockmgr_recursed, lockmgr_rw, lockmgr_waiters, lockstatus, lockmgr_assert — lockmgr family of functions
#include <sys/lockmgr.h> void
lockinit(struct lock *lkp, int prio, const char *wmesg, int timo, int flags); void
lockdestroy(struct lock *lkp); int
lockmgr(struct lock *lkp, u_int flags, struct mtx *ilk); int
lockmgr_args(struct lock *lkp, u_int flags, struct mtx *ilk, const char *wmesg, int prio, int timo); int
lockmgr_args_rw(struct lock *lkp, u_int flags, struct rwlock *ilk, const char *wmesg, int prio, int timo); void
lockmgr_disown(struct lock *lkp); void
lockmgr_printinfo(struct lock *lkp); int
lockmgr_recursed(struct lock *lkp); int
lockmgr_rw(struct lock *lkp, u_int flags, struct rwlock *ilk); int
lockmgr_waiters(struct lock *lkp); int
lockstatus(struct lock *lkp);
lockmgr_assert(struct lock *lkp, int what);
DESCRIPTION¶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:
- A pointer to the lock to initialize.
- The priority passed to sleep(9).
- The lock message. This is used for both debugging output and sleep(9).
- The timeout value passed to sleep(9).
- The flags the lock is to be initialized with:
- Enable adaptive spinning for this lock if the kernel is compiled with the ADAPTIVE_LOCKMGRS option.
- Allow recursive exclusive locks.
- Disable lock profiling for this lock.
- Allow exclusive locks only.
- Instruct witness(4) to ignore this lock.
- witness(4) should log messages about duplicate locks being acquired.
- Disable ktr(4) logging for this lock.
- Use timo during a sleep; otherwise, 0 is used.
- A pointer to the lock to manipulate.
- Flags indicating what action is to be taken.
- Acquire a shared lock. If an exclusive lock is currently held, it will be downgraded.
- Acquire an exclusive lock. If an exclusive lock is
already held, and
LK_CANRECURSEis not set, the system will panic(9).
- 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.
- Upgrade a shared lock to an exclusive lock. If this call fails, the shared lock is lost. During the upgrade, the shared lock could be temporarily dropped. Attempts to upgrade an exclusive lock will cause a panic(9).
- Release the lock. Releasing a lock that is not held can cause a panic(9).
- 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 in <sys/lockmgr.h>.)
- Fail if operation has slept.
- Do not allow the call to sleep. This can be used to test the lock.
- Skip the witness(4) checks for this instance.
- Allow recursion on an exclusive lock. For every lock there must be a release.
- Unlock the interlock (which should be locked already).
- An interlock mutex for controlling group access to the
LK_INTERLOCKis specified, lockmgr() and lockmgr_rw() assume ilk is currently owned and not recursed, and will return it unlocked. See mtx_assert(9).
LK_TIMO_DEFAULT. The lockmgr_disown() function switches the owner from the current thread to be
LK_KERNPROC,if the lock is already held. The lockmgr_printinfo() function prints debugging information about the lock. It is used primarily by VOP_PRINT(9) functions. The lockmgr_recursed() function returns true if the lock is recursed, 0 otherwise. The lockmgr_waiters() function returns true if the lock has waiters, 0 otherwise. The lockstatus() function returns the status of the lock in relation to the current thread. When compiled with options INVARIANTS and options INVARIANT_SUPPORT, the lockmgr_assert() function tests lkp for the assertions specified in what, and panics if they are not met. One of the following assertions must be specified:
- Assert that the current thread has either a shared or an exclusive lock on the lkp lock pointed to by the first argument.
- Assert that the current thread has a shared lock on the lkp lock pointed to by the first argument.
- Assert that the current thread has an exclusive lock on the lkp lock pointed to by the first argument.
- Assert that the current thread has no lock on the lkp lock pointed to by the first argument.
- Assert that the current thread has a recursed lock on lkp.
- Assert that the current thread does not have a recursed lock on lkp.
RETURN VALUES¶The lockmgr() and lockmgr_rw() functions return 0 on success and non-zero on failure. The lockstatus() function returns:
- An exclusive lock is held by the current thread.
- An exclusive lock is held by someone other than the current thread.
- A shared lock is held.
- The lock is not held by anyone.
ERRORS¶lockmgr() and lockmgr_rw() fail if:
LK_FORCEUPGRADEwas requested and another thread had already requested a lock upgrade.
LK_NOWAITwas set, and a sleep would have been required.
LK_SLEEPFAILwas set and lockmgr() or lockmgr_rw() did sleep.
PCATCHwas set in the lock priority, and a signal was delivered during a sleep. Note the
PCATCHwas set in the lock priority, a signal was delivered during a sleep, and the system call is to be restarted.
- a non-zero timeout was given, and the timeout expired.
LK_INTERLOCKis passed in the flags argument to lockmgr() or lockmgr_rw(), the ilk must be held prior to calling lockmgr() or lockmgr_rw(), and will be returned unlocked. 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.
SEE ALSO¶condvar(9), locking(9), mutex(9), rwlock(9), sleep(9), sx(9), mtx_assert(9), panic(9), VOP_PRINT(9)
AUTHORS¶This manual page was written by Chad David ⟨email@example.com⟩.
|June 16, 2009||Debian|