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	  Don't 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 man page was written by Doug Rabson.