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DM(4)                 DragonFly Kernel Interfaces Manual                 DM(4)


NAME

     dm - Device-mapper disk driver


SYNOPSIS

     device dm


DESCRIPTION

     The dm driver provides the capability of creating one or more virtual
     disks based on the target mapping.

     This document assumes that you're familiar with how to generate kernels,
     how to properly configure disks and 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 DragonFly.

     Currently, the linear, zero, error, crypt, and stripe targets are
     implemented.  In order to compile in support for dm, you must add a line
     similar to the following to your kernel configuration file:

           device    dm    #device-mapper disk device

     dm may create linear mapped devices, zero, and error block devices.  Zero
     and error block devices are used mostly for testing.  Linear devices are
     used to create virtual disks with linearly mapped virtual blocks to
     blocks on real disk.  dm Device-mapper devices are controlled through the
     /dev/mapper/control device.  For controlling this device ioctl(2) calls
     are used.  For the implementation of the communication channel, the
     proplib(3) library is used.  The protocol channel is defined as a proplib
     dictionary with needed values.  For more details, look at
     sys/dev/disk/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:

           0 10240 linear /dev/da0s1a 384

     dm 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.  dm 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.


SEE ALSO

     proplib(3), dmsetup(8), fsck(8), lvm(8), mount(8), newfs(8)


HISTORY

     The device-mapper disk driver first appeared in NetBSD 6.0.

     It was then brought into DragonFly 2.7 by Alex Hornung.


AUTHORS

     Adam Hamsik <haad@NetBSD.org> implemented the dm driver for NetBSD.

     Brett Blymn <blymn@NetBSD.org>, Reinoud Zandijk <reinoud@NetBSD.org>, and
     Bill Stouder-Studenmund <wrstuden@NetBSD.org> provided guidance and
     answered questions about the NetBSD implementation.


BUGS

     This driver is still work-in-progress--there can be bugs.

DragonFly 5.7-DEVELOPMENT        July 28, 2010       DragonFly 5.7-DEVELOPMENT

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