devmapper

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 Go to latest Published: Jun 15, 2015 License: Apache-2.0 Imports: 24 Imported by: 0

README

devicemapper - a storage backend based on Device Mapper

Theory of operation

The device mapper graphdriver uses the device mapper thin provisioning module (dm-thinp) to implement CoW snapshots. For each devicemapper graph location (typically /var/lib/docker/devicemapper, $graph below) a thin pool is created based on two block devices, one for data and one for metadata. By default these block devices are created automatically by using loopback mounts of automatically created sparse files.

The default loopback files used are $graph/devicemapper/data and $graph/devicemapper/metadata. Additional metadata required to map from docker entities to the corresponding devicemapper volumes is stored in the $graph/devicemapper/json file (encoded as Json).

In order to support multiple devicemapper graphs on a system, the thin pool will be named something like: docker-0:33-19478248-pool, where the 0:33 part is the minor/major device nr and 19478248 is the inode number of the $graph directory.

On the thin pool, docker automatically creates a base thin device, called something like docker-0:33-19478248-base of a fixed size. This is automatically formatted with an empty filesystem on creation. This device is the base of all docker images and containers. All base images are snapshots of this device and those images are then in turn used as snapshots for other images and eventually containers.

options

The devicemapper backend supports some options that you can specify when starting the docker daemon using the --storage-opt flags. This uses the dm prefix and would be used something like docker -d --storage-opt dm.foo=bar.

Here is the list of supported options:

  • dm.basesize

    Specifies the size to use when creating the base device, which limits the size of images and containers. The default value is 10G. Note, thin devices are inherently "sparse", so a 10G device which is mostly empty doesn't use 10 GB of space on the pool. However, the filesystem will use more space for the empty case the larger the device is. Warning: This value affects the system-wide "base" empty filesystem that may already be initialized and inherited by pulled images. Typically, a change to this value will require additional steps to take effect: 1) stop docker -d, 2) rm -rf /var/lib/docker, 3) start docker -d.

    Example use:

    docker -d --storage-opt dm.basesize=20G

  • dm.loopdatasize

    Specifies the size to use when creating the loopback file for the "data" device which is used for the thin pool. The default size is 100G. Note that the file is sparse, so it will not initially take up this much space.

    Example use:

    docker -d --storage-opt dm.loopdatasize=200G

  • dm.loopmetadatasize

    Specifies the size to use when creating the loopback file for the "metadadata" device which is used for the thin pool. The default size is 2G. Note that the file is sparse, so it will not initially take up this much space.

    Example use:

    docker -d --storage-opt dm.loopmetadatasize=4G

  • dm.fs

    Specifies the filesystem type to use for the base device. The supported options are "ext4" and "xfs". The default is "ext4"

    Example use:

    docker -d --storage-opt dm.fs=xfs

  • dm.mkfsarg

    Specifies extra mkfs arguments to be used when creating the base device.

    Example use:

    docker -d --storage-opt "dm.mkfsarg=-O ^has_journal"

  • dm.mountopt

    Specifies extra mount options used when mounting the thin devices.

    Example use:

    docker -d --storage-opt dm.mountopt=nodiscard

  • dm.datadev

    Specifies a custom blockdevice to use for data for the thin pool.

    If using a block device for device mapper storage, ideally both datadev and metadatadev should be specified to completely avoid using the loopback device.

    Example use:

    docker -d --storage-opt dm.datadev=/dev/sdb1 --storage-opt dm.metadatadev=/dev/sdc1

  • dm.metadatadev

    Specifies a custom blockdevice to use for metadata for the thin pool.

    For best performance the metadata should be on a different spindle than the data, or even better on an SSD.

    If setting up a new metadata pool it is required to be valid. This can be achieved by zeroing the first 4k to indicate empty metadata, like this:

    ``dd if=/dev/zero of=$metadata_dev bs=4096 count=1```

    Example use:

    docker -d --storage-opt dm.datadev=/dev/sdb1 --storage-opt dm.metadatadev=/dev/sdc1

  • dm.blocksize

    Specifies a custom blocksize to use for the thin pool. The default blocksize is 64K.

    Example use:

    docker -d --storage-opt dm.blocksize=512K

  • dm.blkdiscard

    Enables or disables the use of blkdiscard when removing devicemapper devices. This is enabled by default (only) if using loopback devices and is required to res-parsify the loopback file on image/container removal.

    Disabling this on loopback can lead to much faster container removal times, but will make the space used in /var/lib/docker directory not be returned to the system for other use when containers are removed.

    Example use:

    docker -d --storage-opt dm.blkdiscard=false

Documentation

Index

Constants

View Source 
const (
	BlkGetSize64 = C.BLKGETSIZE64
	BlkDiscard   = C.BLKDISCARD

	LoopSetFd       = C.LOOP_SET_FD
	LoopCtlGetFree  = C.LOOP_CTL_GET_FREE
	LoopGetStatus64 = C.LOOP_GET_STATUS64
	LoopSetStatus64 = C.LOOP_SET_STATUS64
	LoopClrFd       = C.LOOP_CLR_FD
	LoopSetCapacity = C.LOOP_SET_CAPACITY
)

IOCTL consts

View Source 
const (
	LoFlagsAutoClear = C.LO_FLAGS_AUTOCLEAR
	LoFlagsReadOnly  = C.LO_FLAGS_READ_ONLY
	LoFlagsPartScan  = C.LO_FLAGS_PARTSCAN
	LoKeySize        = C.LO_KEY_SIZE
	LoNameSize       = C.LO_NAME_SIZE
)

Variables

View Source 
var (
	DefaultDataLoopbackSize     int64  = 100 * 1024 * 1024 * 1024
	DefaultMetaDataLoopbackSize int64  = 2 * 1024 * 1024 * 1024
	DefaultBaseFsSize           uint64 = 10 * 1024 * 1024 * 1024
	DefaultThinpBlockSize       uint32 = 128 // 64K = 128 512b sectors
)
View Source 
var (
	ErrTaskRun                = errors.New("dm_task_run failed")
	ErrTaskSetName            = errors.New("dm_task_set_name failed")
	ErrTaskSetMessage         = errors.New("dm_task_set_message failed")
	ErrTaskSetAddNode         = errors.New("dm_task_set_add_node failed")
	ErrTaskSetRo              = errors.New("dm_task_set_ro failed")
	ErrTaskAddTarget          = errors.New("dm_task_add_target failed")
	ErrTaskSetSector          = errors.New("dm_task_set_sector failed")
	ErrTaskGetInfo            = errors.New("dm_task_get_info failed")
	ErrTaskGetDriverVersion   = errors.New("dm_task_get_driver_version failed")
	ErrTaskSetCookie          = errors.New("dm_task_set_cookie failed")
	ErrNilCookie              = errors.New("cookie ptr can't be nil")
	ErrAttachLoopbackDevice   = errors.New("loopback mounting failed")
	ErrGetBlockSize           = errors.New("Can't get block size")
	ErrUdevWait               = errors.New("wait on udev cookie failed")
	ErrSetDevDir              = errors.New("dm_set_dev_dir failed")
	ErrGetLibraryVersion      = errors.New("dm_get_library_version failed")
	ErrCreateRemoveTask       = errors.New("Can't create task of type DeviceRemove")
	ErrRunRemoveDevice        = errors.New("running removeDevice failed")
	ErrInvalidAddNode         = errors.New("Invalide AddNoce type")
	ErrGetLoopbackBackingFile = errors.New("Unable to get loopback backing file")
	ErrLoopbackSetCapacity    = errors.New("Unable set loopback capacity")
	ErrBusy                   = errors.New("Device is Busy")
)
View Source 
var (
	DmGetLibraryVersion    = dmGetLibraryVersionFct
	DmGetNextTarget        = dmGetNextTargetFct
	DmLogInitVerbose       = dmLogInitVerboseFct
	DmSetDevDir            = dmSetDevDirFct
	DmTaskAddTarget        = dmTaskAddTargetFct
	DmTaskCreate           = dmTaskCreateFct
	DmTaskDestroy          = dmTaskDestroyFct
	DmTaskGetInfo          = dmTaskGetInfoFct
	DmTaskGetDriverVersion = dmTaskGetDriverVersionFct
	DmTaskRun              = dmTaskRunFct
	DmTaskSetAddNode       = dmTaskSetAddNodeFct
	DmTaskSetCookie        = dmTaskSetCookieFct
	DmTaskSetMessage       = dmTaskSetMessageFct
	DmTaskSetName          = dmTaskSetNameFct
	DmTaskSetRo            = dmTaskSetRoFct
	DmTaskSetSector        = dmTaskSetSectorFct
	DmUdevWait             = dmUdevWaitFct
	LogWithErrnoInit       = logWithErrnoInitFct
)

Functions

func BlockDeviceDiscard 

func BlockDeviceDiscard(path string) error

func DevmapperLogCallback 

func DevmapperLogCallback(level C.int, file *C.char, line C.int, dm_errno_or_class C.int, message *C.char)

func FindLoopDeviceFor 

func FindLoopDeviceFor(file *os.File) *os.File

func GetBlockDeviceSize 

func GetBlockDeviceSize(file *os.File) (uint64, error)

func GetLibraryVersion 

func GetLibraryVersion() (string, error)

func Init 

func Init(home string, options []string) (graphdriver.Driver, error)

func LogInitVerbose 

func LogInitVerbose(level int)

func LoopbackSetCapacity 

func LoopbackSetCapacity(file *os.File) error

func Mounted 

func Mounted(mountpoint string) (bool, error)

func ProbeFsType 

func ProbeFsType(device string) (string, error)

func RemoveDevice 

func RemoveDevice(name string) error

Useful helper for cleanup

func SetDevDir 

func SetDevDir(dir string) error

func UdevWait 

func UdevWait(cookie uint) error

Types

type AddNodeType 

type AddNodeType int
const (
	AddNodeOnResume AddNodeType = iota
	AddNodeOnCreate
)

type CDmTask 

type CDmTask C.struct_dm_task

type CLoopInfo64 

type CLoopInfo64 C.struct_loop_info64

type DevInfo 

type DevInfo struct {
	Hash          string `json:"-"`
	DeviceId      int    `json:"device_id"`
	Size          uint64 `json:"size"`
	TransactionId uint64 `json:"transaction_id"`
	Initialized   bool   `json:"initialized"`
	// contains filtered or unexported fields
}

func (*DevInfo) DevName 

func (info *DevInfo) DevName() string

func (*DevInfo) Name 

func (info *DevInfo) Name() string

type DevStatus 

type DevStatus struct {
	DeviceId            int
	Size                uint64
	TransactionId       uint64
	SizeInSectors       uint64
	MappedSectors       uint64
	HighestMappedSector uint64
}

type DeviceSet 

type DeviceSet struct {
	MetaData
	sync.Mutex // Protects Devices map and serializes calls into libdevmapper

	TransactionId    uint64
	NewTransactionId uint64
	// contains filtered or unexported fields
}

func NewDeviceSet 

func NewDeviceSet(root string, doInit bool, options []string) (*DeviceSet, error)

func (*DeviceSet) AddDevice 

func (devices *DeviceSet) AddDevice(hash, baseHash string) error

func (*DeviceSet) DeleteDevice 

func (devices *DeviceSet) DeleteDevice(hash string) error

func (*DeviceSet) GetDeviceStatus 

func (devices *DeviceSet) GetDeviceStatus(hash string) (*DevStatus, error)

func (*DeviceSet) HasActivatedDevice 

func (devices *DeviceSet) HasActivatedDevice(hash string) bool

func (*DeviceSet) HasDevice 

func (devices *DeviceSet) HasDevice(hash string) bool

func (*DeviceSet) List 

func (devices *DeviceSet) List() []string

func (*DeviceSet) MountDevice 

func (devices *DeviceSet) MountDevice(hash, path, mountLabel string) error

func (*DeviceSet) ResizePool 

func (devices *DeviceSet) ResizePool(size int64) error

func (*DeviceSet) Shutdown 

func (devices *DeviceSet) Shutdown() error

func (*DeviceSet) Status 

func (devices *DeviceSet) Status() *Status

func (*DeviceSet) UnmountDevice 

func (devices *DeviceSet) UnmountDevice(hash string) error

type DevmapperLogger 

type DevmapperLogger interface {
	// contains filtered or unexported methods
}

type DiskUsage 

type DiskUsage struct {
	Used  uint64
	Total uint64
}

type Driver 

type Driver struct {
	*DeviceSet
	// contains filtered or unexported fields
}

func (*Driver) Cleanup 

func (d *Driver) Cleanup() error

func (*Driver) Create 

func (d *Driver) Create(id, parent string) error

func (*Driver) Exists 

func (d *Driver) Exists(id string) bool

func (*Driver) Get 

func (d *Driver) Get(id, mountLabel string) (string, error)

func (*Driver) Put 

func (d *Driver) Put(id string)

func (*Driver) Remove 

func (d *Driver) Remove(id string) error

func (*Driver) Status 

func (d *Driver) Status() [][2]string

func (*Driver) String 

func (d *Driver) String() string

type Info 

type Info struct {
	Exists        int
	Suspended     int
	LiveTable     int
	InactiveTable int
	OpenCount     int32
	EventNr       uint32
	Major         uint32
	Minor         uint32
	ReadOnly      int
	TargetCount   int32
}

type LoopInfo64 

type LoopInfo64 struct {
	// contains filtered or unexported fields
}

type MetaData 

type MetaData struct {
	Devices map[string]*DevInfo `json:"Devices"`
	// contains filtered or unexported fields
}

type Status 

type Status struct {
	PoolName         string
	DataLoopback     string
	MetadataLoopback string
	Data             DiskUsage
	Metadata         DiskUsage
	SectorSize       uint64
}

type Task 

type Task struct {
	// contains filtered or unexported fields
}

func TaskCreate 

func TaskCreate(tasktype TaskType) *Task

func (*Task) AddTarget 

func (t *Task) AddTarget(start, size uint64, ttype, params string) error

func (*Task) GetDriverVersion 

func (t *Task) GetDriverVersion() (string, error)

func (*Task) GetInfo 

func (t *Task) GetInfo() (*Info, error)

func (*Task) GetNextTarget 

func (t *Task) GetNextTarget(next uintptr) (nextPtr uintptr, start uint64,
	length uint64, targetType string, params string)

func (*Task) Run 

func (t *Task) Run() error

func (*Task) SetAddNode 

func (t *Task) SetAddNode(addNode AddNodeType) error

func (*Task) SetCookie 

func (t *Task) SetCookie(cookie *uint, flags uint16) error

func (*Task) SetMessage 

func (t *Task) SetMessage(message string) error

func (*Task) SetName 

func (t *Task) SetName(name string) error

func (*Task) SetRo 

func (t *Task) SetRo() error

func (*Task) SetSector 

func (t *Task) SetSector(sector uint64) error

type TaskType 

type TaskType int
const (
	DeviceCreate TaskType = iota
	DeviceReload
	DeviceRemove
	DeviceRemoveAll
	DeviceSuspend
	DeviceResume
	DeviceInfo
	DeviceDeps
	DeviceRename
	DeviceVersion
	DeviceStatus
	DeviceTable
	DeviceWaitevent
	DeviceList
	DeviceClear
	DeviceMknodes
	DeviceListVersions
	DeviceTargetMsg
	DeviceSetGeometry
)

Source Files

View all Source files

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