VOP_LOCK(9)						   BSD Kernel Developer's Manual					       VOP_LOCK(9)

NAME

     VOP_LOCK, VOP_UNLOCK, VOP_ISLOCKED, vn_lock -- serialize access to a vnode

SYNOPSIS

     #include <sys/param.h>
     #include <sys/lock.h>
     #include <sys/vnode.h>

     int
     VOP_LOCK(struct vnode *vp, int flags);

     int
     VOP_UNLOCK(struct vnode *vp, int flags);

     int
     VOP_ISLOCKED(struct vnode *vp);

     int
     vn_lock(struct vnode *vp, int flags);

DESCRIPTION

     These calls are used to serialize access to the file system, such as to prevent two writes to the same file from happening at the same time.

     The arguments are:

     vp     The vnode being locked or unlocked.

     flags  One of the lock request types:

		  LK_SHARED	 Shared lock.
		  LK_EXCLUSIVE	 Exclusive lock.
		  LK_UPGRADE	 Shared-to-exclusive upgrade.
		  LK_DOWNGRADE	 Exclusive-to-shared downgrade.
		  LK_RELEASE	 Release any type of lock.
		  LK_DRAIN	 Wait for all lock activity to end.

	    The lock type may be or'ed with these lock flags:

		  LK_NOWAIT	 Do not sleep to wait for lock.
		  LK_SLEEPFAIL	 Sleep, then return failure.
		  LK_CANRECURSE  Allow recursive exclusive lock.
		  LK_NOWITNESS	 Instruct witness(4) to ignore this instance.

	    The lock type may be or'ed with these control flags:

		  LK_INTERLOCK	 Specify when the caller already has a simple lock (VOP_LOCK() will unlock the simple lock after getting the
				 lock).
		  LK_RETRY	 Retry until locked.

	    Kernel code should use vn_lock() to lock a vnode rather than calling VOP_LOCK() directly.  vn_lock() also does not want a thread spec-
	    ified as argument but it assumes curthread to be used.

RETURN VALUES

     Zero is returned on success, otherwise an error is returned.

SEE ALSO

     vnode(9)

AUTHORS

     This manual page was written by Doug Rabson.

BSD
								 February 25, 2008							       BSD