Add vcount.9 / count_dev.9.

Touched up a bit and added some consistency to the text by your's truly.

PR:		23745
Submitted by:	Andrew Stevenson <andrew@ugh.net.au>

share/man/man9/Makefile

@@ -28,7 +28,7 @@ MAN9=	CONDSPLASSERT.9 DELAY.9 KASSERT.9 MD5.9 SPLASSERT.9 \
 	scheduler.9 sleep.9 sleepqueue.9 spl.9 store.9 style.9 suser.9 swi.9 \
 	time.9 timeout.9 tvtohz.9 \
 	uio.9 \
-	vget.9 vnode.9 vput.9 vref.9 vrele.9 vslock.9
+	vcount.9 vget.9 vnode.9 vput.9 vref.9 vrele.9 vslock.9
 
 MAN9+=	device.9 device_add_child.9 device_delete_child.9 device_enable.9 \
 	device_find_child.9 device_get_children.9 \
@@ -214,6 +214,8 @@ MLINKS+=sbuf.9 sbuf_data.9
 MLINKS+=sbuf.9 sbuf_len.9
 MLINKS+=sbuf.9 sbuf_delete.9
 
+MLINKS+=vcount.9 count_dev.9
+
 MLINKS+=zone.9 zalloc.9
 MLINKS+=zone.9 zfree.9
 MLINKS+=zone.9 zinit.9

share/man/man9/vcount.9

@@ -0,0 +1,68 @@
+.\" -*- nroff -*-
+.\"
+.\" Copyright (c) 2000 Andrew Stevenson
+.\"
+.\" 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.
+.\"
+.\" If this man page travels to places exotic (like projects other than
+.\" FreeBSD) I would love to hear about it.
+.\"     Andrew <andrew@ugh.net.au>
+.\"
+.\" $FreeBSD$
+.\"
+.Dd February 6th, 2001
+.Os
+.Dt VCOUNT 9
+.Sh NAME
+.Nm vcount ,
+.Nm count_dev
+.Nd get total number of references to a device.
+.Sh SYNOPSIS
+.Fd #include <sys/types.h>
+.Fd #include <sys/conf.h>
+.Fd #include <sys/vnode.h>
+.Ft int
+.Fn vcount "struct vnode *vp"
+.Ft int
+.Fn count_dev "dev_t dev"
+.Sh DESCRIPTION
+.Fn vcount
+is used to get the number of references to a particular device.
+It allows for the fact that multiple vnodes may reference the same device.
+.Fn count_dev
+does the same thing as vcount,
+but takes a dev_t rather than a vnode pointer as an argument.
+.Sh RETURN VALUES
+.Fn vcount
+and
+.Fn count_dev
+both return the number of references to the device.
+.Sh SEE ALSO
+.Xr VFS 9 ,
+.Xr vnode 9 ,
+.Pa src/sys/kern/vfs_subr.c
+.Sh AUTHORS
+This man page was written by
+.An Andrew Stevenson .