Crate devicemapper [−] [src]
Low-level devicemapper configuration of the running kernel.
Overview
Linux's devicemapper allows the creation of block devices whose storage is mapped to other block devices in useful ways, either by changing the location of its data blocks, or performing some operation on the data itself. This is a low-level facility that is used by higher-level volume managers such as LVM2. Uses may include:
- Dividing a large block device into smaller logical volumes (dm-linear)
- Combining several separate block devices into a single block device with better performance and/or redundancy (dm-raid)
- Encrypting a block device (dm-crypt)
- Performing Copy-on-Write (COW) allocation of a volume's blocks enabling fast volume cloning and snapshots (dm-thin)
- Configuring a smaller, faster block device to act as a cache for a larger, slower one (dm-cache)
- Verifying the contents of a read-only volume (dm-verity)
Usage
Before they can be used, DM devices must be created using
DM::device_create(), have a mapping table loaded using
DM::table_load(), and then activated with
DM::device_suspend(). (This function is used for both suspending
and activating a device.) Once activated, they can be used as a
regular block device, including having other DM devices map to
them.
Devices have "active" and "inactive" mapping tables. See function descriptions for which table they affect.
Modules
| IEC |
International Electrotechnical Commission Units Standards |
Structs
| Bytes |
Structure to represent bytes |
| CacheDev |
DM Cache device |
| CacheDevPerformance |
Cache dev performance data |
| CacheDevUsage |
Cache usage |
| CacheDevWorkingStatus |
Status values of a cache device when it is working |
| DM |
Context needed for communicating with devicemapper. |
| DataBlocks |
A type for Data Blocks as used by the thin pool. |
| Device |
A struct containing the device's major and minor numbers |
| DmFlags |
Flags used by devicemapper. |
| DmName |
The borrowed version of the DM identifier. |
| DmNameBuf |
The owned version of the DM identifier. |
| DmUuid |
The borrowed version of the DM identifier. |
| DmUuidBuf |
The owned version of the DM identifier. |
| FlakeyTargetParams |
Target params for flakey target |
| LinearDev |
A DM construct of combined Segments |
| LinearDevTargetTable |
A target table for a linear device. Such a table allows flakey targets as well as linear targets. |
| LinearTargetParams |
Struct representing params for a linear target |
| MetaBlocks |
A type for Meta Data blocks as used by the thin pool. MetaBlocks have a kernel defined constant size of META_BLOCK_SIZE |
| Sectors |
A separate type to store counts and offsets expressed in 512-byte sectors. |
| TargetLine |
One line of a device mapper table. |
| TargetType |
The borrowed version of the DM identifier. |
| TargetTypeBuf |
The owned version of the DM identifier. |
| ThinDev |
DM construct for a thin block device |
| ThinDevId |
A thindev id is a 24 bit number, i.e., its bit width is not a power of 2. |
| ThinDevWorkingStatus |
Status values for a thin device that is working |
| ThinPoolDev |
DM construct to contain thin provisioned devices |
| ThinPoolUsage |
Contains values indicating the thinpool's used vs total allocations for metadata and data blocks. |
| ThinPoolWorkingStatus |
Status of a working thin pool, i.e, one that does not have status Fail Note that this struct is incomplete. It does not contain every value that can be parsed from a data line, as some of those values are of unknown format. |
Enums
| CacheDevStatus |
Return type of CacheDev::status() |
| DevId |
Used as a parameter for functions that take either a Device name or a Device UUID. |
| DmError |
Super error type, with constructors distinguishing outer errors from core errors. |
| ErrorEnum |
A very simple breakdown of outer layer errors. |
| LinearDevTargetParams |
Target params for linear dev. These are either flakey or linear. |
| ThinPoolNoSpacePolicy |
Policy if no space on device |
| ThinPoolStatus |
Top-level thinpool status that indicates if it is working or failed. |
| ThinPoolStatusSummary |
Indicates if a working thinpool is working optimally, or is experiencing a non-fatal error condition. |
| ThinStatus |
Thin device status. |
Constants
| SECTOR_SIZE |
disk sector size in bytes |
Traits
| DmDevice |
A trait capturing some shared properties of DM devices. |
Functions
| device_exists |
Check if a device of the given name exists. |
| devnode_to_devno |
Get a device number from a device node. Return None if the device is not a block device; devicemapper is not interested in other sorts of devices. Return None if the device appears not to exist. |
Type Definitions
| DmResult |
return result for DM functions |