xref: /freebsd/share/man/man9/VOP_LOCK.9 (revision fab63cc4136a3c0d156d1b82497e894b10d0fe59)

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.\" Copyright (c) 1996 Doug Rabson
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.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 serialise 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.