OpenBSD-4.6/share/man/man4/vnd.4

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.\"	$OpenBSD: vnd.4,v 1.21 2008/03/17 16:30:36 sobrado Exp $
.\"	$NetBSD: vnd.4,v 1.1 1995/12/30 18:10:48 thorpej Exp $
.\"
.\" Copyright (c) 1995 Jason R. Thorpe.
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.\"	This product includes software developed for the NetBSD Project
.\"	by Jason R. Thorpe.
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.Dd $Mdocdate: March 17 2008 $
.Dt VND 4
.Os
.Sh NAME
.Nm vnd
.Nd vnode disk driver
.Sh SYNOPSIS
.Cd "pseudo-device vnd" Op Ar count
.Sh DESCRIPTION
The
.Nm
driver provides a disk-like interface to a file.
This is useful for a variety of applications, including swap files and
building miniroot or floppy disk images.
There are two variants, the traditional
.Nm
that bypasses the buffer cache and thus is suitable for swap on files, but
not for building disk-images, and the
.Nm svnd
.Po
.Dq safe
.Nm
.Pc
variant that goes
through the buffer cache, thereby maintaining cache-coherency after the
block-device is closed which makes it suitable for creating disk images.
The latter is not good for swapping on, though.
.Pp
This document assumes familiarity with how to generate kernels and
how to properly configure disks and pseudo-devices in a kernel
configuration file.
.Pp
In order to compile in support for
.Nm vnd
devices, a line similar to the following must be present in the kernel
configuration file:
.Bd -unfilled -offset indent
pseudo-device	vnd	4	# vnode disk driver
.Ed
.Pp
The
.Ar count
argument is how many
.Nm vnds
memory is allocated for at boot time.
In this example, no more than 4
.Nm vnds
may be configured.
.Pp
There is a run-time utility that is used for configuring
.Nm vnds .
See
.Xr vnconfig 8
for more information.
.Sh IOCTL INTERFACE
The following
.Xr ioctl 2
calls are defined in
.Aq Pa dev/vndioctl.h :
.Bl -tag -width Ds
.It Dv VNDIOCSET Fa "struct vnd_ioctl *"
Associate the file
.Va vnd_file
with a
.Nm
pseudo device, optionally encrypted using the Blowfish cipher and the key
specified in
.Va vnd_key
of length
.Va vnd_keylen .
Encryption only works with
.Nm svnd
devices.
The size of the configured device is returned in
.Va vnd_size .
.Bd -literal -offset indent
struct vnd_ioctl {
	char	*vnd_file;
	off_t	vnd_size;
	u_char	*vnd_key;
	int	vnd_keylen;
};
.Ed
.It Dv VNDIOCCLR Fa "struct vnd_ioctl *"
Disassociate a
.Nm
device.
.It Dv VNDIOCGET Fa "struct vnd_user *"
Get the associated file name, device, inode number, and unit number of a
.Nm
device.
If
.Va vnu_unit
is \-1, information on the
.Nm
device corresponding to the file descriptor passed to
.Xr ioctl 2
will be returned.
Otherwise,
.Va vnu_unit
may contain the unit number of another
.Nm
device.
This allows for opening just
.Li vnd0
and querying all available devices.
.Bd -literal -offset indent
struct vnd_user {
	char	vnufile[VNDNLEN];
	int	vnu_unit;
	dev_t	vnu_dev;
	ino_t	vnu_ino;
};
.Ed
.El
.Pp
Additionally, some
.Xr disklabel 8
related
.Xr ioctl 2
calls defined in
.Aq Pa sys/disklabel.h
are available:
.Dv DIOCGDINFO ,
.Dv DIOCSDINFO ,
.Dv DIOCWDINFO ,
and
.Dv DIOCWLABEL .
They are documented in
.Xr sd 4 .
.Sh FILES
.Bl -tag -width /dev/{,r}{,s}vnd* -compact
.It Pa /dev/{,r}{,s}vnd*
.Nm
device special files
.El
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr sd 4 ,
.Xr disklabel 5 ,
.Xr MAKEDEV 8 ,
.Xr config 8 ,
.Xr disklabel 8 ,
.Xr fdisk 8 ,
.Xr fsck 8 ,
.Xr mount 8 ,
.Xr newfs 8 ,
.Xr vnconfig 8
.Sh HISTORY
The
.Nm
disk driver was originally written at the University of
Utah.
The
.Nm svnd
variant was first seen in
.Ox 2.1 .
.Sh BUGS
The
.Nm
driver does not work if the file does not reside in a local filesystem.
However the
.Nm svnd
variant does.