new file mode 100644

@@ -0,0 +1,73 @@

+## 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 locaion (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 creates 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 `0:30` 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 formated on creation and contains just an

+empty filesystem. 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 somthing 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.

+

+    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``

+

@@ -13,12 +13,14 @@ import (

 	"path"

 	"path/filepath"

 	"strconv"

+	"strings"

 	"sync"

 	"syscall"

 	"time"

 	"github.com/dotcloud/docker/daemon/graphdriver"

 	"github.com/dotcloud/docker/pkg/label"

+	"github.com/dotcloud/docker/pkg/units"

 	"github.com/dotcloud/docker/utils"

 )

@@ -65,6 +67,11 @@ type DeviceSet struct {

 	TransactionId    uint64

 	NewTransactionId uint64

 	nextDeviceId     int

+

+	// Options

+	dataLoopbackSize     int64

+	metaDataLoopbackSize int64

+	baseFsSize           uint64

 }

 type DiskUsage struct {

@@ -378,8 +385,8 @@ func (devices *DeviceSet) setupBaseImage() error {

 	// Ids are 24bit, so wrap around

 	devices.nextDeviceId = (id + 1) & 0xffffff

-	utils.Debugf("Registering base device (id %v) with FS size %v", id, DefaultBaseFsSize)

-	info, err := devices.registerDevice(id, "", DefaultBaseFsSize)

+	utils.Debugf("Registering base device (id %v) with FS size %v", id, devices.baseFsSize)

+	info, err := devices.registerDevice(id, "", devices.baseFsSize)

 	if err != nil {

 		_ = deleteDevice(devices.getPoolDevName(), id)

 		utils.Debugf("\n--->Err: %s\n", err)

@@ -567,12 +574,12 @@ func (devices *DeviceSet) initDevmapper(doInit bool) error {

 		}

 		createdLoopback = !hasData || !hasMetadata

-		data, err := devices.ensureImage("data", DefaultDataLoopbackSize)

+		data, err := devices.ensureImage("data", devices.dataLoopbackSize)

 		if err != nil {

 			utils.Debugf("Error device ensureImage (data): %s\n", err)

 			return err

 		}

-		metadata, err := devices.ensureImage("metadata", DefaultMetaDataLoopbackSize)

+		metadata, err := devices.ensureImage("metadata", devices.metaDataLoopbackSize)

 		if err != nil {

 			utils.Debugf("Error device ensureImage (metadata): %s\n", err)

 			return err

@@ -1091,12 +1098,45 @@ func (devices *DeviceSet) Status() *Status {

 	return status

 }

-func NewDeviceSet(root string, doInit bool) (*DeviceSet, error) {

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

 	SetDevDir("/dev")

 	devices := &DeviceSet{

-		root:     root,

-		MetaData: MetaData{Devices: make(map[string]*DevInfo)},

+		root:                 root,

+		MetaData:             MetaData{Devices: make(map[string]*DevInfo)},

+		dataLoopbackSize:     DefaultDataLoopbackSize,

+		metaDataLoopbackSize: DefaultMetaDataLoopbackSize,

+		baseFsSize:           DefaultBaseFsSize,

+	}

+

+	for _, option := range options {

+		key, val, err := utils.ParseKeyValueOpt(option)

+		if err != nil {

+			return nil, err

+		}

+		key = strings.ToLower(key)

+		switch key {

+		case "dm.basesize":

+			size, err := units.FromHumanSize(val)

+			if err != nil {

+				return nil, err

+			}

+			devices.baseFsSize = uint64(size)

+		case "dm.loopdatasize":

+			size, err := units.FromHumanSize(val)

+			if err != nil {

+				return nil, err

+			}

+			devices.dataLoopbackSize = size

+		case "dm.loopmetadatasize":

+			size, err := units.FromHumanSize(val)

+			if err != nil {

+				return nil, err

+			}

+			devices.metaDataLoopbackSize = size

+		default:

+			return nil, fmt.Errorf("Unknown option %s\n", key)

+		}

 	}

 	if err := devices.initDevmapper(doInit); err != nil {

@@ -27,7 +27,7 @@ type Driver struct {

 }

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

-	deviceSet, err := NewDeviceSet(home, true)

+	deviceSet, err := NewDeviceSet(home, true, options)

 	if err != nil {

 		return nil, err

 	}