.\" -*- 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.
.\"
.Dd January 18, 2016
.Dt VREF 9
.Os
.Sh NAME
.Nm vref , vrefl
.Nd increment the use count for a vnode
.Sh SYNOPSIS
.In sys/param.h
.In sys/vnode.h
.Ft void
.Fn vref "struct vnode *vp"
.Ft void
.Fn vrefl "struct vnode *vp"
.Sh DESCRIPTION
Increment the
.Va v_usecount
field of a vnode.
.Bl -tag -width 2n
.It Fa vp
the vnode to increment
.El
.Pp
Each vnode maintains a reference count of how many parts of the system
are using the vnode.
This allows the system to detect when a vnode is
no longer being used and can be safely recycled for a different file.
.Pp
Any code in the system which is using a vnode (e.g.\& during the
operation of some algorithm or to store in a data structure) should
call
.Fn vref
or
.Fn vrefl .
.Pp
.Fn vref
locks the vnode interlock while
.Fn vrefl
expects the interlock to already be held.
.Sh SEE ALSO
.Xr vget 9 ,
.Xr vnode 9 ,
.Xr vput 9 ,
.Xr vrefcnt 9 ,
.Xr vrele 9
.Sh AUTHORS
This manual page was written by
.An Doug Rabson .