Device Mapper

The device mapper puts a layer between block devices and the application. Typical applications are RAID systems or Encrypted File Systems. To have the device mapper running enable device mapper support in the kernel. Set the following Device Drivers > Multiple Devices Driver Support (RAID and LVM):

CONFIG_BLK_DEV_DM=y
CONFIG_DM_MULTIPATH=y
CONFIG_DM_CRYPT=y

emerge device-mapper

If you run baselayout2 then add the runscripts rc-update add device-mapper boot

The device-mapper contains dmsetup that creates block device nodes in

/dev/mapper/<device name>

cat /proc/devices shows that it is running.

Truecrypt makes use of dmsetup and creates a node as truecrypt3

dmsetup info truecrypt3 will give info

dmsetup table truecrypt3 will show its table

It is also possible to create and remove such devices manually

dmsetup create<device name> --notable

dmsetup remove<device name>


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