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/share/man/man9/vrele.9

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  1.\" -*- nroff -*-
  2.\"
  3.\" Copyright (c) 1996 Doug Rabson
  4.\" Copyright (c) 2010 Konstantin Belousov <kib@FreeBSD.org>
  5.\"
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 30.\" $FreeBSD$
 31.\"
 32.Dd November 20, 2010
 33.Dt VRELE 9
 34.Os
 35.Sh NAME
 36.Nm vput ,
 37.Nm vrele ,
 38.Nm vunref
 39.Nd decrement the use count for a vnode
 40.Sh SYNOPSIS
 41.In sys/param.h
 42.In sys/vnode.h
 43.Ft void
 44.Fn vput "struct vnode *vp"
 45.Ft void
 46.Fn vrele "struct vnode *vp"
 47.Ft void
 48.Fn vunref "struct vnode *vp"
 49.Sh DESCRIPTION
 50Decrement the
 51.Va v_usecount
 52field of a vnode.
 53.Bl -tag -width 2n
 54.It Fa vp
 55the vnode to decrement
 56.El
 57.Pp
 58The
 59.Fn vrele
 60function takes an unlocked vnode and returns with the vnode unlocked.
 61.Pp
 62The
 63.Fn vput
 64function should be given a locked vnode as argument, the vnode is unlocked
 65after the function returned.
 66The
 67.Fn vput
 68is operationally equivalent to calling
 69.Xr VOP_UNLOCK 9
 70followed by
 71.Xr vrele 9 ,
 72with less overhead.
 73.Pp
 74The
 75.Fn vunref
 76function takes a locked vnode as argument, and returns with the vnode locked.
 77.Pp
 78Any code in the system which signified its use of a vnode by usecount
 79should call one of the listed function to decrement use counter.
 80If the
 81.Va v_usecount
 82field of the non-doomed vnode reaches zero, then it will be inactivated
 83and placed on the free list.
 84Since the functions might need to call VOPs for the vnode, the
 85.Va Giant
 86mutex should be conditionally locked around the call.
 87.Pp
 88The hold count for the vnode is always greater or equal to the usecount.
 89Non-forced unmount fails when mount point owns a vnode that has non-zero
 90usecount, see
 91.Xr vflush 9 .
 92.Sh SEE ALSO
 93.Xr vget 9 ,
 94.Xr vnode 9 ,
 95.Xr vref 9 ,
 96.Xr vrefcnt 9
 97.Sh AUTHORS
 98This manual page was written by
 99.An Doug Rabson
100and
101.An Konstantin Belousov .