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Bring documentation up to date, add a few more vnconfig examples.

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This commit is contained in:
Matthew Dillon 1999-09-21 01:03:11 +00:00
parent 3927c47b04
commit c35bc469bd
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=51490
2 changed files with 42 additions and 4 deletions
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18
share/man/man4/vn.4
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@ -44,9 +44,15 @@
.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 mini-root
or floppy disk images.
driver uses swap or a file as backing store to abstract-out a character and
block device which may then be used like a disk. The
.Nm
driver supports both labeled and unlabeled pseudo-disks and is useful for
a variety of applications, including swap files and building mini-root,
floppy, or CDRom disk images.
.Nm
may also be used to create temporary swap-backed filesystems, such as /tmp,
in a somewhat less memory-hungry manner then MFS.
.Pp
This document assumes that you're familiar with how to generate kernels,
how to properly configure disks and pseudo-devices in a kernel
@ -67,6 +73,9 @@ argument is how many
memory is allocated for a boot time. In this example, no more than 4
.Nm vn Ns 's
may be configured.
.Nm
may also exist as a kernel module to be automatically loaded into the
system when you run the vnconfig command for the first time.
.Pp
There is a run-time utility that is used for configuring
.Nm vn Ns 's .
@ -82,7 +91,8 @@ driver does not work if the file does not reside in a local filesystem.
.Pp
.Sh HISTORY
The vnode disk driver was originally written at the University of
Utah.
Utah and was substantially modified by FreeBSD developers to add
swap-backed support.
.Sh SEE ALSO
.Xr config 8 ,
.Xr fsck 8 ,

28
usr.sbin/vnconfig/vnconfig.8
View File

@ -225,6 +225,34 @@ Unmounts (disables)
.Pp
Configures and enables all devices specified in
.Pa /etc/vntab .
.Pp
.Dl vnconfig -s labels -c vn0 somebackingfile
.Dl disklabel -r -w vn0 auto
.Dl disklabel -e vn0
.Pp
Is an example of how to configure a file-backed VN disk with a disk label
and to initialize and then edit the label. Once you create the label, you
can partition your 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 VN disk after a crash by vnconfig'ing the same file again
and using the VN configuration already stored in the file rather then
relabeling and recreating the filesystem. It is even possible to fsck the
VN partitions that previously contained filesystems.
.Pp
.Dl vnconfig -e -s labels,reserve -S 400m vn0
.Dl disklabel -r -w vn1 auto
.Dl newfs /dev/rvn1c
.Dl mount /dev/vn1c /usr/obj
.Pp
Is an example of a swap-backed 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 /usr/obj. Swap-backed VN
devices are recoverable after a crash if you (A) use the reserve flag, and if
(B) the same swap is reserved as was the last time, meaning that such
vnconfig's would have to be run in your rc.local. In general, though, you
only use swap-backed VN devices to hold information you don't mind losing
on every reboot.
.Sh SEE ALSO
.Xr mount 2 ,
.Xr swapon 2 ,