.\" -*- nroff -*-
.\"
.\" Copyright (c) 1996 Doug Rabson
.\"
.\" All rights reserved.
.\"
.\" This program is free software.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $Id: VOP_LOCK.9,v 1.1 1997/03/03 18:00:25 dfr Exp $
.\"
.Dd July 24, 1996
.Os
.Dt VOP_LOCK 9
.Sh NAME
.Nm VOP_LOCK ,
.Nm VOP_UNLOCK ,
.Nm VOP_ISLOCKED
.Nd serialize access to a vnode
.Sh SYNOPSIS
.Fd #include <sys/vnode.h>
.Ft int
.Fn VOP_LOCK "struct vnode *vp"
.Ft int
.Fn VOP_UNLOCK "struct vnode *vp"
.Ft int
.Fn VOP_ISLOCKED "struct vnode *vp"
.Sh DESCRIPTION
.Pp
The arguments are:
.Bl -tag -width vp
.It Ar vp
the vnode being locked or unlocked
.El
.Pp
These calls are used to serialize access to the filesystem, for
instance to prevent two writes to the same file from happening at the
same time.
.Sh RETURN VALUES
Zero is returned on success, otherwise an error is returned.
.Sh PSEUDOCODE
.Bd -literal
struct vopnode {
    int von_flag;
    /*
     * Other filesystem 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;
}
.Ed
.Sh SEE ALSO
.Xr vnode 9
.Sh AUTHORS
This man page was written by Doug Rabson.