devmappercontrol

devmappercontrol refers to the control interface used by the Linux device-mapper subsystem to manage device-mapper devices. It is implemented in the kernel as part of the device-mapper driver and is accessed from user space through the special device node /dev/mapper/control. The interface enables user-space tools to create, configure, modify, and remove device-mapper mappings.

The control interface operates through a set of ioctls and a message-based protocol defined in the kernel headers. User-space components such as libdevmapper and the dmsetup tool communicate with the kernel via /dev/mapper/control to perform actions like creating a mapping, loading a target table, suspending or resuming a device, and removing mappings. The mapping description specifies how a virtual device maps to real block devices or other targets, enabling features such as linear layouts, striped devices, mirrors, snapshots, and thin provisioning.

In practice, devmappercontrol is most visible through tools that manage device-mapper devices. LVM2, used for logical volume management, relies on this interface to implement logical volumes. dmsetup, the canonical command-line tool for device-mapper, provides a direct user-space interface to perform operations such as creating names, loading tables, and listing devices, all by talking to /dev/mapper/control.

Security and administration: access to /dev/mapper/control requires privileged permissions, as misconfiguration can affect essential block devices and data integrity. The devmappercontrol interface is a core component of the Linux storage stack, widely used by kernel-based storage technologies and third-party software that relies on flexible block device mappings.

See also: device-mapper, dmsetup, libdevmapper, LVM2, thin provisioning.