VOP_LOCK(9)	       FreeBSD 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, struct thread *td);

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

     int
     VOP_ISLOCKED(struct vnode *vp, struct thread *td);

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

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_EXCLUPGRADE  First 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_REENABLE	  Lock is to be reenabled after drain.
		  LK_NOPAUSE	  No spinloop.

	    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.
		  LK_NOOBJ	  Do not create object.

     td     Thread context to use for the locks.

     Kernel code should use vn_lock() to lock a vnode rather than calling
     VOP_LOCK() directly.

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

PSEUDOCODE
     struct vopnode {

	 int von_flag;
	 /*
	  * Other file system specific data.
	  */

	 ...;
     };
     #define VON_LOCKED      1
     #define VON_WANTED      2
     #define VTOVON(vp)      ((struct vopnode *) (vp)->v_data)

     int
     vop_lock(struct vnode *vp)
     {

	 struct vopnode* vop;

     start:

	 while (vp->v_flag & VXLOCK) {
	     vp->v_flag |= VXWANT;
	     tsleep((caddr_t)vp, PINOD, "voplk1", 0);

	 }
	 if (vp->v_tag == VT_NON)
	     return ENOENT;

	 vop = VTOVON(vp);
	 if (vop->von_flag & VON_LOCKED) {
	     vop->von_flag |= VON_WANTED;
	     tsleep((caddr_t) vop, PINOD, "voplk2", 0);
	     goto start;

	 }

	 vop->von_flag |= VON_LOCKED;

	 return 0;
     }

     int
     vop_unlock(struct vnode *vp)
     {

	 struct vopnode *vop = VTOVON(vp);

	 if ((vop->von_flag & VON_LOCKED) == 0) {
	     panic("vop_unlock not locked");

	 }
	 vop->von_flag &= ~VON_LOCKED;
	 if (vop->von_flag & VON_WANTED) {
	     vop->von_flag &= ~VON_WANTED;
	     wakeup((caddr_t) vop);

	 }

	 return 0;
     }

     int
     vop_islocked(struct vnode *vp)
     {

	 struct vopnode *vop = VTOVON(vp);

	 if (vop->von_flag & VON_LOCKED)
	     return 1;

	 else
	     return 0;

     }

SEE ALSO
     vnode(9)

AUTHORS
     This manual page was written by Doug Rabson.

FreeBSD 7.2			 July 24, 1996			   FreeBSD 7.2

NAME - SYNOPSIS - DESCRIPTION - RETURN VALUES - PSEUDOCODE - SEE ALSO - 
AUTHORS -