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lockstatus (9)

>> lockstatus (9) ( FreeBSD man: Ядро )

BSD mandoc

NAME



lockinit

 
lockdestroy

 
lockcount

 
lockmgr

 
lockstatus

 
lockmgr_printinfo

 - lockmgr family of functions

SYNOPSIS

   #include <sys/types.h>
   #include <sys/lock.h>
   #include <sys/lockmgr.h>
void lockinit (struct lock *lkp int prio const char *wmesg int timo int flags);
void lockdestroy (struct lock *lkp);
int lockcount (struct lock *lkp);
int lockmgr (struct lock *lkp u_int flags struct mtx *interlkp struct thread *td);
int lockstatus (struct lock *lkp struct thread *td);
void lockmgr_printinfo (struct lock *lkp);

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:

Fa lkp

A pointer to the lock to initialize.

Fa prio

The priority passed to sleep(9).

Fa wmesg

The lock message. This is used for both debugging output and sleep(9).

Fa timo

The timeout value passed to sleep(9).

Fa 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_NOSHARE: Allow exclusive locks only.
LK_TIMELOCK: Use Fa 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 Fa 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:

Fa lkp

A pointer to the lock to manipulate.

Fa 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 Er 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 panic(9).
LK_UPGRADE: 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).
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 in In sys/lockmgr.h . )
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 already).

Fa interlkp

An interlock mutex for controlling group access to the lock. If LK_INTERLOCK is specified, lockmgr ();
assumes Fa interlkp is currently owned and not recursed, and will return it unlocked. See mtx_assert9.

Fa td

A thread responsible for this call. NULL becomes LK_KERNPROC

The lockstatus ();
function returns the status of the lock in relation to the Vt thread passed to it. Note that if Fa 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_PRINT9 functions.

RETURN VALUES

The lockcount ();
function returns an integer greater than or equal to zero.

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 Fa td .
LK_EXCLOTHER: An exclusive lock is held by someone other than the thread Fa td .
LK_SHARED: A shared lock is held.
0: The lock is not held by anyone.

ERRORS

lockmgr ();
fails if:

Bq Er EBUSY: LK_FORCEUPGRADE was requested and another thread had already requested a lock upgrade.
Bq Er EBUSY: LK_NOWAIT was set, and a sleep would have been required.
Bq Er ENOLCK: LK_SLEEPFAIL was set and lockmgr ();
did sleep.
Bq Er EINTR: PCATCH was set in the lock priority, and a signal was delivered during a sleep. Note the Er ERESTART error below.
Bq Er ERESTART: PCATCH was set in the lock priority, a signal was delivered during a sleep, and the system call is to be restarted.
Bq Er EWOULDBLOCK: a non-zero timeout was given, and the timeout expired.

LOCKS

If LK_INTERLOCK is passed in the Fa flags argument to lockmgr (,);
the Fa interlkp must be held prior to calling lockmgr (,);
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.