usr.sbin/vnconfig/vnconfig.8

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.\"     @(#)vnconfig.8	8.1 (Berkeley) 6/5/93
.\" $FreeBSD: src/usr.sbin/vnconfig/vnconfig.8,v 1.14.2.8 2003/01/04 22:35:53 keramida Exp $
.\"
.Dd January 19, 2022
.Dt VNCONFIG 8
.Os
.Sh NAME
.Nm vnconfig
.Nd configure and enable vnode disks
.Sh SYNOPSIS
.Nm
.Op Fl cdeguvTZ
.Op Fl s Ar options
.Op Fl r Ar options
.Op Fl S Ar value
.Ar special_file Op Ar regular_file
.Op Ar feature
.Nm
.Fl a
.Op Fl cdeguv
.Op Fl s Ar options
.Op Fl r Ar options
.Op Fl f Ar config_file
.Nm
.Fl l
.Op Ar special_file Ar ...
.Sh DESCRIPTION
The
.Nm
command configures, enables and lists vnode pseudo disk devices.
The first form of the command will associate the special file
.Ar special_file
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.
If you want to use swap backing store for your device instead of a file,
you can leave
.Ar regular_file
out and specify the size of the block device
with the
.Fl S
option.
.Pp
Options indicate an action to be performed:
.Bl -tag -width indent
.It Fl a
Read a command file and performs the
specified actions for each device/file pair.
.It Fl c
Configure the device.
If successful, references to
.Ar special_file
will access the contents of
.Ar regular_file .
.Pp
A
.Nm vn
device is autocloned if
.Ar special_file
is given as
.Pa vn ,
the name of the resulting device is printed on stdout.
.It Fl d
Disable (if possible) the specified feature.
.It Fl e
Configure the device and enables any
.Ar feature
that was specified.
If no feature was specified,
.Fl e
is the same as
.Fl c .
.It Fl f Ar config_file
Specify configuration file.
Default is
.Pa /etc/vntab .
.It Fl g
Fiddle global options.
.It Fl l Ar special_file Ar ...
List the
.Nm vn
devices and indicate which ones are in use.
If a
.Ar special_file
list is given, only those devices will be described.
.It Fl r Ar options
Reset
.Ar options ,
which is a comma separated string of options.
The list of allowed options and their meanings are:
.Bl -tag -width "reserve"
.It Cm reserve
Pre-reserve the blocks underlying the file or swap backing store.
Currently only works for swap backing store.
This option also disables on-the-fly freeing of
the underlying backing store (for example, when you remove a large file).
Use this option if you wish to avoid long-term fragmentation of the backing
store.
Also note that when this option is used, the initial contents of the
backing store may contain garbage rather than zeros.
It may even be possible to
recover the prior contents of a swap-backed
.Nm vn
across a reboot if the
.Nm vn
device
is configured before any swap is allocated by the system.
.It Cm follow
Debug flow in the
.Xr vn 4
driver.
.It Cm debug
Debug data in the
.Xr vn 4
driver.
.It Cm io
Debug
.Tn I/O
in the
.Xr vn 4
driver.
.It Cm all
Turn on all options.
.It Cm none
Turn off all options.
.El
.It Fl s Ar options
Set
.Ar options ,
which is a comma separated string of options.
The list of allowed options and their meanings are the same as for the
.Fl r
option.
.It Fl S Xo
.Sm off
.Ar value
.Brq Cm k , m , g , t
.Sm on
.Xc
If no regular file is specified,
.Nm vn
will use swap for backing store.
This option specifies the size of the device.
For example,
.Sq 23m
for
23 megabytes.
In the absence of a size modifier,
.Cm m
is implied.
The
.Nm vn
device will round the size up to a machine page boundary.
Filesystems up to 7.9 terabytes are supported.
When specified along with
a regular file, this option overrides the regular file's size insofar as
.Nm vn
is concerned.
.It Fl T
When a regular file is specified,
.Nm
will
.Fn ftruncate
the file to length 0 first.
Normally you should also specify the
.Fl S
option to set the size of the file.
This option also creates the file if it did not previously exist.
This option is only meaningful if the
.Fl S
option has been specified.
.It Fl Z
When a regular file is specified,
.Nm
will zero the contents of the file to
ensure that all blocks have been allocated by the filesystem.
This option is only meaningful if the
.Fl S
option has been specified.
.It Fl u
Disable and ``unconfigure'' the device.
.It Fl v
Print messages to stdout describing actions taken.
.El
.Pp
If no action option is given,
.Fl c
is assumed.
.Pp
The
.Ar feature
argument specifies a feature that can be enabled via the
.Fl e
option:
.Bl -tag -width indent
.It Cm swap
Swapping is enabled on the special file.
See
.Xr swapon 2 .
.It Cm mountro= Ns Ar mount_point
The special file is mounted read-only on
.Ar mount_point .
See
.Xr mount 2 .
.It Cm mountrw= Ns Ar mount_point
The special file is mounted read-write on
.Ar mount_point .
See
.Xr mount 2 .
.It Cm mount= Ns Ar mount_point
Same as
.Cm mountrw= Ns Ar mount_point .
.El
.Pp
A configuration file contains one line per device/file pair in the form:
.Bd -literal
	special_file	regular_file	[feature]
.Ed
.Pp
where fields are separated by white space.
Lines starting with
.Sq #
are ignored.
The previously described action options serve to configure, enable,
disable or unconfigure all devices in the configuration file.
.Sh FILES
.Bl -tag -width /etc/vntab -compact
.It Pa /etc/vntab
default configuration file for
.Fl a
option
.El
.Sh EXAMPLES
.Dl vnconfig vn /tmp/diskimage
.Pp
Configures an autocloned vnode disk,
the name of the resulting device is printed, e.g.\&
.Pa vn4 .
.Pp
.Dl vnconfig vn0 /tmp/diskimage
.Pp
Configures the vnode disk
.Pa vn0 .
.Pp
.Dl vnconfig -e vn0 /var/swapfile swap
.Pp
Configures
.Pa vn0
and enables swapping on it.
.Pp
.Dl vnconfig -c -v /dev/vn0 cdimage.iso
.Dl mount -t cd9660 -o ro /dev/vn0 /mnt
.Pp
Mount an ISO9660 CD image file.
.Pp
.Dl umount /mnt
.Dl vnconfig -u vn0
.Pp
Unmount the CD image file.
.Pp
.Dl vnconfig -d vn0 myfilesystem mount=/mnt
.Pp
Unmounts (disables)
.Pa vn0 .
.Pp
.Dl vnconfig -ae
.Pp
Configures and enables all devices specified in
.Pa /etc/vntab .
.Pp
.Dl vnconfig -c vn0 somebackingfile
.Dl disklabel -r -w vn0s0 auto
.Dl disklabel -e vn0s0
.Pp
Is an example of how to configure a file-backed
.Nm vn
disk with a disk label
and to initialize and then edit the label.
Once you create the label, you
can partition your
.Nm vn
disk and, for example, create a filesystem on one of the partitions.
If you are using a file as backing store, it may be possible
to recover your
.Nm vn
disk after a crash by
.Nm Ns 'ing
the same file again and using the
.Nm vn
configuration already stored in the file rather than
relabeling and recreating the filesystem.
It is even possible to
.Xr fsck 8
the
.Nm vn
partitions that previously contained filesystems.
.Pp
.Dl vnconfig -e -s reserve -S 400m vn1
.Dl disklabel -r -w vn1s0 auto
.Dl newfs /dev/vn1s0
.Dl mount /dev/vn1s0 /usr/obj
.Pp
Is an example of a swap-backed
.Nm vn
disk configuration.
This example assumes
that you have at least 400 megabytes of swap free (and hopefully much more).
The swap space is pre-reserved in order to maintain maximum performance.
We then label the disk, newfs it, and mount it as
.Pa /usr/obj .
Swap-backed
.Nm vn
devices are recoverable after a crash if you (A) use the
.Cm reserve
option, and if
(B) the same swap is reserved as was the last time, meaning that such
.Nm Ns 's
would have to be run in your
.Xr rc.local 8 .
In general, though, you only use swap-backed
.Nm vn
devices to hold information you don't mind losing on every reboot.
.Sh SEE ALSO
.Xr mount 2 ,
.Xr swapon 2 ,
.Xr unmount 2 ,
.Xr vn 4