NetBSD/usr.sbin/vnconfig/vnconfig.8

.\"	$NetBSD: vnconfig.8,v 1.50 2023/10/21 23:42:03 gdt Exp $
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jason R. Thorpe.
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.\" Copyright (c) 1993 University of Utah.
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.\"	@(#)vnconfig.8	8.1 (Berkeley) 6/5/93
.\"
.Dd October 20, 2023
.Dt VNDCONFIG 8
.Os
.Sh NAME
.Nm vndconfig
.Nd configure vnode disks
.Sh SYNOPSIS
.Nm
.\" Fcf:lm:rt:uvz
.Op Fl cirvz
.Op Fl f Ar disktab
.Op Fl t Ar typename
.Ar vnode_disk
.Ar regular_file
.Op Ar geomspec
.Nm
.Fl u
.Op Fl Fv
.Ar vnode_disk
.Nm
.Fl l
.Op Fl m Ar min
.Op Ar vnode_disk ...
.Sh DESCRIPTION
The
.Nm
command configures vnode pseudo disk devices.
It will associate the vnode disk
.Ar vnode_disk
with the regular file
.Ar regular_file
allowing the latter to be accessed as though it were a disk.
Hence a regular file within the filesystem can be used for swapping
or can contain a filesystem that is mounted in the name space.
The
.Ar vnode_disk
is a special file of raw partition or name of vnode disk like
.Pa vnd0 .
.Pp
By default, accesses to the file bypass normal mechanisms and thus
do not read from or fill the filesystem cache.
Because the typical approach is to access the file only via
.Xr vnd 4 ,
or at least to have regular accesses and
.Xr vnd 4
accesses separated in time, this is generally not problematic.
This bypassing behavior results in not updating the modification
timestamp of the file.
Also, file contents read through the filesystem (and thus the
filesystem's caching layer) may not be the contents written via this
interface, so caution is in order for backups.
The
.Fl i
option may be useful if it is necessary to avoid inconsistent caching.
.Pp
Options indicate an action to be performed:
.Bl -tag -width indent
.It Fl c
Configures the device.
If successful, references to
.Ar vnode_disk
will access the contents of
.Ar regular_file .
.Pp
If
.Ar geomspec
is specified, the vnode device will emulate the specified disk geometry.
The format of the
.Ar geomspec
argument is:
.Bd -ragged -offset indent
.Sm off
.Xo Ar secsize Li / Ar nsectors Li /
.Ar ntracks Li / Ar ncylinders Xc
.Sm on
.Ed
.Pp
If geometry is not specified, the kernel will choose a default based on 1MB
cylinders.
.Ar secsize
is the number of bytes per sector.
It must be a power of two, and at least 512.
.Ar nsectors
is the number of sectors per track.
.Ar ntracks
is the number of tracks per cylinder.
.Ar ncylinders
is the number of cylinders in the device.
.It Fl F
Force unconfiguration if the device is in use.
Does not imply
.Fl u .
.It Fl f Ar disktab
Specifies that the
.Fl t
option should look up in
.Ar disktab
instead of in
.Pa /etc/disktab .
.It Fl i
Configure the device to use regular file I/O even when direct I/O using
bmap/strategy would be possible.
.It Fl l
List the vnd devices and indicate which ones are in use.
If one or more specific
.Ar vnode_disks
are given, then only those will be described.
.It Fl m Ar min
Together with
.Fl l
and if no specific devices are given,
causes at least
.Ar min
devices to be listed.
The default for
.Ar min
is 4,
but all vnd devices up to (and sometimes just beyond)
the highest numbered vnd device configured since
the system last booted will be listed.
If
.Ar min
is set to 0,
then only vnd devices currently in use will be shown.
.It Fl r
Configure the device as read-only.
.It Fl t Ar typename
If configuring the device, look up
.Ar typename
in
.Pa /etc/disktab
and use the geometry specified in the entry.
This option and the
.Ar geomspec
argument are mutually exclusive.
.It Fl u
Unconfigures the device.
.It Fl v
Print messages to stdout describing actions taken.
.It Fl z
Assume that
.Ar regular_file
is a compressed disk image in cloop2 format, and configure it
read-only.
See the
.Xr vndcompress 1
manpage on how to create such an image.
.El
.Pp
If no action option
.Op Fl clu
is given,
.Fl c
is assumed.
.Sh FILES
.Bl -tag -width /etc/disktab -compact
.It Pa /dev/rvnd??
.It Pa /dev/vnd??
.It Pa /etc/disktab
.El
.Sh EXIT STATUS
.Nm
will exit with status 0 if the operation requested
completed successfully,
or 1 otherwise.
Unsuccessful completion can be caused by unknown or
incorrectly used options;
attempting to configure a vnd that is already configured;
or unconfigure one that is not, or without
.Fl F ,
one which is still in use;
or if devices are specified that do not exist or are not
.Xr vnd 4
devices, giving an improper geometry, etc.
.Sh EXAMPLES
.Dl vndconfig vnd0 /tmp/diskimage
or
.Dl vndconfig /dev/rvnd0c /tmp/diskimage
.Pp
Configures the vnode disk
.Pa vnd0 .
Please note that use of the second form of the command is discouraged because
it requires knowledge of the raw partition which varies between architectures.
For the first form, be aware that there must not be a file
.Ar vnd0
in the current directory, or it will be assumed to be the vnd device to
be configured (which will usually fail.)
.Pp
.Dl vndconfig vnd0 /tmp/floppy.img 512/18/2/80
.Pp
Configures the vnode disk
.Pa vnd0
emulating the geometry of 512 bytes per sector, 18 sectors per track,
2 tracks per cylinder, and 80 cylinders total.
.Pp
.Dl vndconfig vnd0 /tmp/image.udf 2048/1/1/0
.Pp
Configures the vnode disk
.Pa vnd0
for an UDF image to be used with
.Xr mount_udf 8 .
.Pp
.Dl vndconfig -t floppy vnd0 /tmp/floppy.img
.Pp
Configures the vnode disk
.Pa vnd0
using the geometry specified in the
.Pa floppy
entry in
.Pa /etc/disktab .
.Pp
.Dl vndconfig -u vnd0
.Pp
Unconfigures the
.Pa vnd0
device.
.Pp
To obtain status on all vnd devices listed in
.Pa /dev
(assuming a system where the
.Sq d
partition is the whole device
.Pq Dv RAW_PART ) ,
use:
.Pp
.Dl vndconfig -l /dev/vnd*d
.Pp
Using
.Dl vndconfig -m0 -l /dev/vnd*d
will omit those devices that are not in use, whereas
.Dl vndconfig -l
will list all devices known to the kernel (at least 4
without
.Fl m )
regardless of what might appear in
.Pa /dev
(or elsewhere.)
.Sh SEE ALSO
.Xr vndcompress 1 ,
.Xr opendisk 3 ,
.Xr vnd 4 ,
.Xr mount 8 ,
.Xr swapctl 8 ,
.Xr umount 8
.Sh HISTORY
The
.Nm vnconfig
command appeared in
.Nx 1.0 .
It was renamed to
.Nm
in
.Nx 7.0
for consistency with other similar commands.
(The original name was also retained as an alternative
for backwards compatibility.)