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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 specified 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.