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Improve English, sort sections, various other stuff.

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.\" $NetBSD: dm.4,v 1.1 2008/12/22 02:28:28 haad Exp $
.\" $NetBSD: dm.4,v 1.2 2008/12/22 08:52:37 wiz Exp $
.\"
.\" Copyright (c) 1996, 1997 The NetBSD Foundation, Inc.
.\" All rights reserved.
@ -38,81 +38,104 @@
The
.Nm
driver provides the capability of creating one or more virtual disks
based on target mapping.
based on the target mapping.
.Pp
This document assumes that you're familiar with how to generate kernels,
how to properly configure disks and pseudo-devices in a kernel configuration file,
and how to partition disks. This driver is used by linux lvm2tools to create/manage
lvm in NetBSD.
This document assumes that you're familiar with how to generate
kernels, how to properly configure disks and pseudo-devices in a
kernel configuration file, and how to partition disks.
This driver is used by the Linux lvm2tools to create and manage
lvm in
.Nx .
.Pp
Note that there are
.Pa linear, zero, error
targets implemented now.
Each component partition should be offset at least 2 sectors
Currently, the
.Pa linear , zero ,
and
.Pa error
targets are implemented.
Each component partition should be offset at least 2 sectors
from the beginning of the component disk.
This avoids potential conflicts between the component disk's
disklabel and the
.Nm Ns 's
disklabel and
.Nm Ap s
disklabel.
In i386 it is offset 65s. Where 63 sectors are initial boot
sectors and 2 sectors are used for disklabel which is set to
be read-only.
In i386 it is offset by 65 sectors, where 63 sectors are the initial
boot sectors and 2 sectors are used for the disklabel which is set
to be read-only.
.Pp
In order to compile in support for the
In order to compile in support for
.Nm ,
you must add a line similar
to the following to your kernel configuration file:
you must add a line similar to the following to your kernel
configuration file:
.Bd -unfilled -offset indent
pseudo-device dm #device-mapper disk device
.Ed
.Pp
A
.Nm
may create linear mapped devices, zero and error block devices. Zero
and error block devices are used mostly for testing.
.Pa Linear
devices are used to create Virtual disks with lineary mapped virtual blocks
to blocks on real disk.
may create linear mapped devices, zero, and error block devices.
Zero and error block devices are used mostly for testing.
.Pa Linear
devices are used to create virtual disks with linearly mapped virtual
blocks to blocks on real disk.
.Nm
Device-mapper devices are controlled throught /dev/mapper/control device. For
controlling this device Ioctl calls are used. For implementation of communication
channel proplib library is used. Protocol channel is defined as on proplib
dictionary with needed values. For more reference look at sys/dev/dm/netbsd-dm.h.
.Nm
Before any device can be used every device-mapper disk device must be initialized.
For initialization is needed to pass one line to kernel driver in a form of proplib
dictionary. Every device can have more than one tables active.
Device-mapper devices are controlled through the
.Pa /dev/mapper/control
device.
For controlling this device
.Xr ioctl 2
calls are used.
For the implementation of the communication channel,
the
.Xr proplib 3
library is used.
The protocol channel is defined as a proplib dictionary with needed
values.
For more details, look at
.Pa sys/dev/dm/netbsd-dm.h .
Before any device can be used, every device-mapper disk device must
be initialized.
For initialization one line must be passed to the kernel driver in
the form of a proplib dictionary.
Every device can have more than one table active.
An example for such a line is:
.Bd -unfilled -offset indent
0 10240 linear /dev/wd1a 384
.Ed
.Pp
.Nm
The first parameter is start sector for table defined with this line, the second is length in
sectors which is described with this table. The third parameter is target name. All other parts
of this line depends on choosen target.
The first parameter is the start sector for the table defined with
this line, the second is the length in sectors which is described
with this table.
The third parameter is the target name.
All other parts of this line depend on the chosen target.
.Nm
For linear target there are two additional parameters the first parameter describes disk device
on which device-mapper disk is mapped. The second parameter is offset on this disk from start of
disk/partition.
.Sh WARNINGS
This driver is still work-in-progress there can be bugs.
.Sh AUTHORS
.An Adam Hamsik Aq haad@NetBSD.org
implemented the device-mapper driver
.Nx .
.Pp
.An Brett Blymn Aq blymn@NetBSD.org ,
.An Reinoud Zandijk Aq reinoud@netbsd.org and
.An Bill Stouder-Studenmund Aq wrstuden@netbsd.org
provided guidance and answered questions about NetBSD implementation.
For the linear target, there are two additional parameters:
The first parameter describes the disk device to which the
device-mapper disk is mapped.
The second parameter is the offset on this disk from the start of
the disk/partition.
.Sh SEE ALSO
.Xr config 1 ,
.Xr proplib 3 ,
.Xr MAKEDEV 8 ,
.Xr lvm 8 ,
.Xr dmsetup 8 ,
.Xr fsck 8 ,
.Xr lvm 8 ,
.Xr mount 8 ,
.Xr newfs 8 ,
.Xr proplib 3
.Xr newfs 8
.Sh HISTORY
The device-mapper disk driver first appeared in NetBSD 6.0.
The device-mapper disk driver first appeared in
.Nx 6.0 .
.Sh AUTHORS
.An Adam Hamsik Aq haad@NetBSD.org
implemented the device-mapper driver for
.Nx .
.Pp
.An Brett Blymn Aq blymn@NetBSD.org ,
.An Reinoud Zandijk Aq reinoud@NetBSD.org ,
and
.An Bill Stouder-Studenmund Aq wrstuden@NetBSD.org
provided guidance and answered questions about the
.Nx
implementation.
.Sh BUGS
This driver is still work-in-progress\(emthere can be bugs.