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DM(4)                        Device Drivers Manual                       DM(4)

     dm - Device-mapper disk driver

     pseudo-device dm

     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 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 NetBSD.

     Currently, the linear, zero, and 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 dm's disklabel.  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.

     In order to compile in support for dm, you must add a line similar to the
     following to your kernel configuration file:

           pseudo-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/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/wd1a 384

     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.

     For the linear target, there are two additional parameters: The fourth
     parameter describes the disk device to which the device-mapper disk is
     mapped.  The fifth parameter is the offset on this disk from the start of
     the disk/partition.

     config(1), proplib(3), dmsetup(8), fsck(8), lvm(8), MAKEDEV(8), mount(8),

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

     Adam Hamsik <haad@NetBSD.org> implemented the device-mapper driver for

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

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

NetBSD 10.99                     April 4, 2015                    NetBSD 10.99