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.\" Copyright (c) 1996 Doug Rabson
.\" Copyright (c) 2010 Konstantin Belousov <kib@FreeBSD.org>
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.\" $FreeBSD: release/9.1.0/share/man/man9/vrele.9 215798 2010-11-24 12:34:25Z kib $
.\"
.Dd November 20, 2010
.Dt VRELE 9
.Os
.Sh NAME
.Nm vput ,
.Nm vrele ,
.Nm vunref
.Nd decrement the use count for a vnode
.Sh SYNOPSIS
.In sys/param.h
.In sys/vnode.h
.Ft void
.Fn vput "struct vnode *vp"
.Ft void
.Fn vrele "struct vnode *vp"
.Ft void
.Fn vunref "struct vnode *vp"
.Sh DESCRIPTION
Decrement the
.Va v_usecount
field of a vnode.
.Bl -tag -width 2n
.It Fa vp
the vnode to decrement
.El
.Pp
The
.Fn vrele
function takes an unlocked vnode and returns with the vnode unlocked.
.Pp
The
.Fn vput
function should be given a locked vnode as argument, the vnode is unlocked
after the function returned.
The
.Fn vput
is operationally equivalent to calling
.Xr VOP_UNLOCK 9
followed by
.Xr vrele 9 ,
with less overhead.
.Pp
The
.Fn vunref
function takes a locked vnode as argument, and returns with the vnode locked.
.Pp
Any code in the system which signified its use of a vnode by usecount
should call one of the listed function to decrement use counter.
If the
.Va v_usecount
field of the non-doomed vnode reaches zero, then it will be inactivated
and placed on the free list.
Since the functions might need to call VOPs for the vnode, the
.Va Giant
mutex should be conditionally locked around the call.
.Pp
The hold count for the vnode is always greater or equal to the usecount.
Non-forced unmount fails when mount point owns a vnode that has non-zero
usecount, see
.Xr vflush 9 .
.Sh SEE ALSO
.Xr vget 9 ,
.Xr vnode 9 ,
.Xr vref 9 ,
.Xr vrefcnt 9
.Sh AUTHORS
This manual page was written by
.An Doug Rabson
and
.An Konstantin Belousov .