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IMedium Interface Reference

The IMedium interface represents virtual storage for a machine's hard disks, CD/DVD or floppy drives. More...

Inheritance diagram for IMedium:

## Public Member Functions
void | setIds (in boolean setImageId, in wstringUUID imageId, in boolean setParentId, in wstringUUID parentId)
| Changes the UUID and parent UUID for a hard disk medium.
void | refreshState ([retval] out MediumState state)
| If the current medium state (see MediumState) is one of "Created", "Inaccessible" or "LockedRead", then this performs an accessibility check on the medium and sets the value of the state attribute accordingly; that value is also returned for convenience.
void | getSnapshotIds (in wstringUUID machineId, [retval] out wstringUUID[] snapshotIds)
| Returns an array of UUIDs of all snapshots of the given machine where this medium is attached to.
void | lockRead ([retval] out IToken token)
| Locks this medium for reading.
void | lockWrite ([retval] out IToken token)
| Locks this medium for writing.
void | close ()
| Closes this medium.
void | getProperty (in wstring name, [retval] out wstring value)
| Returns the value of the custom medium property with the given name.
void | setProperty (in wstring name, in wstring value)
| Sets the value of the custom medium property with the given name.
void | getProperties (in wstring names, out wstring[] returnNames, [retval] out wstring[] returnValues)
| Returns values for a group of properties in one call.
void | setProperties (in wstring[] names, in wstring[] values)
| Sets values for a group of properties in one call.
void | createBaseStorage (in long long logicalSize, in MediumVariant[] variant, [retval] out IProgress progress)
| Starts creating a hard disk storage unit (fixed/dynamic, according to the variant flags) in the background.
void | deleteStorage ([retval] out IProgress progress)
| Starts deleting the storage unit of this medium.
void | createDiffStorage (in IMedium target, in MediumVariant[] variant, [retval] out IProgress progress)
| Starts creating an empty differencing storage unit based on this medium in the format and at the location defined by the target argument.
void | mergeTo (in IMedium target, [retval] out IProgress progress)
| Starts merging the contents of this medium and all intermediate differencing media in the chain to the given target medium.
void | cloneTo (in IMedium target, in MediumVariant[] variant, in IMedium parent, [retval] out IProgress progress)
| Starts creating a clone of this medium in the format and at the location defined by the target argument.
void | cloneToBase (in IMedium target, in MediumVariant[] variant, [retval] out IProgress progress)
| Starts creating a clone of this medium in the format and at the location defined by the target argument.
void | moveTo (in wstring location, [retval] out IProgress progress)
| Changes the location of this medium.
void | compact ([retval] out IProgress progress)
| Starts compacting of this medium.
void | resize (in long long logicalSize, [retval] out IProgress progress)
| Starts resizing this medium.
void | reset ([retval] out IProgress progress)
| Starts erasing the contents of this differencing medium.
void | changeEncryption (in wstring currentPassword, in wstring cipher, in wstring newPassword, in wstring newPasswordId, [retval] out IProgress progress)
| Starts encryption of this medium.
void | getEncryptionSettings (out wstring cipher, [retval] out wstring passwordId)
| Returns the encryption settings for this medium.
void | checkEncryptionPassword (in wstring password)
| Checks whether the supplied password is correct for the medium.
void | openForIO (in boolean writable, in wstring password, [retval] out IMediumIO mediumIO)
| Open the medium for I/O.
void | resizeAndCloneTo (in IMedium target, in long long logicalSize, in MediumVariant[] variant, in IMedium parent, [retval] out IProgress progress)
| This is a helper function that combines the functionality of IMedium::cloneTo and IMedium::resize.

## Public Attributes
readonly attribute wstringUUID | id
| UUID of the medium.
attribute wstring | description
| Optional description of the medium.
readonly attribute MediumState | state
| Returns the current medium state, which is the last state set by the accessibility check performed by refreshState.
readonly attribute MediumVariant[] | variant
| Returns the storage format variant information for this medium as an array of the flags described at MediumVariant.
attribute wstring | location
| Location of the storage unit holding medium data.
readonly attribute wstring | name
| Name of the storage unit holding medium data.
readonly attribute DeviceType | deviceType
| Kind of device (DVD/Floppy/HardDisk) which is applicable to this medium.
readonly attribute boolean | hostDrive
| True if this corresponds to a drive on the host.
readonly attribute long long | size
| Physical size of the storage unit used to hold medium data (in bytes).
readonly attribute wstring | format
| Storage format of this medium.
readonly attribute IMediumFormat | mediumFormat
| Storage medium format object corresponding to this medium.
attribute MediumType | type
| Type (role) of this medium.
readonly attribute MediumType[] | allowedTypes
| Returns which medium types can selected for this medium.
readonly attribute IMedium | parent
| Parent of this medium (the medium this medium is directly based on).
readonly attribute IMedium[] | children
| Children of this medium (all differencing media directly based on this medium).
readonly attribute IMedium | base
| Base medium of this medium.
readonly attribute boolean | readOnly
| Returns `true` if this medium is read-only and `false` otherwise.
readonly attribute long long | logicalSize
| Logical size of this medium (in bytes), as reported to the guest OS running inside the virtual machine this medium is attached to.
attribute boolean | autoReset
| Whether this differencing medium will be automatically reset each time a virtual machine it is attached to is powered up.
readonly attribute wstring | lastAccessError
| Text message that represents the result of the last accessibility check performed by refreshState.
readonly attribute wstringUUID[] | machineIds
| Array of UUIDs of all machines this medium is attached to.

## Detailed Description

The IMedium interface represents virtual storage for a machine's hard disks, CD/DVD or floppy drives.

It will typically represent a disk image on the host, for example a VDI or VMDK file representing a virtual hard disk, or an ISO or RAW file representing virtual removable media, but can also point to a network location (e.g. for iSCSI targets).

Instances of IMedium are connected to virtual machines by way of medium attachments, which link the storage medium to a particular device slot of a storage controller of the virtual machine. In the VirtualBox API, virtual storage is therefore always represented by the following chain of object links:

- IMachine::storageControllers contains an array of storage controllers (IDE, SATA, SCSI, SAS or a floppy controller; these are instances of IStorageController).

- IMachine::mediumAttachments contains an array of medium attachments (instances of IMediumAttachment created by IMachine::attachDevice), each containing a storage controller from the above array, a port/device specification, and an instance of IMedium representing the medium storage (image file).

  For removable media, the storage medium is optional; a medium attachment with no medium represents a CD/DVD or floppy drive with no medium inserted. By contrast, hard disk attachments will always have an IMedium object attached.

- Each IMedium in turn points to a storage unit (such as a file on the host computer or a network resource) that holds actual data. This location is represented by the location attribute.

Existing media are opened using IVirtualBox::openMedium; new hard disk media can be created with the VirtualBox API using the IVirtualBox::createMedium method. Differencing hard disks (see below) are usually implicitly created by VirtualBox as needed, but may also be created explicitly using createDiffStorage. VirtualBox cannot create CD/DVD or floppy images (ISO and RAW files); these should be created with external tools and then opened from within VirtualBox.

Only for CD/DVDs and floppies, an IMedium instance can also represent a host drive. In that case the id attribute contains the UUID of one of the drives in IHost::DVDDrives or IHost::floppyDrives.

### Media registries

When a medium has been opened or created using one of the aforementioned APIs, it becomes "known" to VirtualBox. Known media can be attached to virtual machines and re-found through IVirtualBox::openMedium. They also appear in the global IVirtualBox::hardDisks, IVirtualBox::DVDImages and IVirtualBox::floppyImages arrays.

Prior to VirtualBox 4.0, opening a medium added it to a global media registry in the VirtualBox.xml file, which was shared between all machines and made transporting machines and their media from one host to another difficult.

Starting with VirtualBox 4.0, media are only added to a registry when they are attached to a machine using IMachine::attachDevice. For backwards compatibility, which registry a medium is added to depends on which VirtualBox version created a machine:

- If the medium has first been attached to a machine which was created by VirtualBox 4.0 or later, it is added to that machine's media registry in the machine XML settings file. This way all information about a machine's media attachments is contained in a single file and can be transported easily.
- For older media attachments (i.e. if the medium was first attached to a machine which was created with a VirtualBox version before 4.0), media continue to be registered in the global VirtualBox settings file, for backwards compatibility.

See IVirtualBox::openMedium for more information.

Media are removed from media registries by the IMedium::close, deleteStorage and mergeTo methods.

### Accessibility checks

VirtualBox defers media accessibility checks until the refreshState method is called explicitly on a medium. This is done to make the VirtualBox object ready for serving requests as fast as possible and let the end-user application decide if it needs to check media accessibility right away or not.

As a result, when VirtualBox starts up (e.g. the VirtualBox object gets created for the first time), all known media are in the "Inaccessible" state, but the value of the lastAccessError attribute is an empty string because no actual accessibility check has been made yet.

After calling refreshState, a medium is considered accessible if its storage unit can be read. In that case, the state attribute has a value of "Created". If the storage unit cannot be read (for example, because it is located on a disconnected network resource, or was accidentally deleted outside VirtualBox), the medium is considered inaccessible, which is indicated by the "Inaccessible" state. The exact reason why the medium is inaccessible can be obtained by reading the lastAccessError attribute.

### Medium types

There are five types of medium behavior which are stored in the type attribute (see MediumType) and which define the medium's behavior with attachments and snapshots.

All media can be also divided in two groups: base media and differencing media. A base medium contains all sectors of the medium data in its own storage and therefore can be used independently. In contrast, a differencing medium is a "delta" to some other medium and contains only those sectors which differ from that other medium, which is then called a parent. The differencing medium is said to be linked to that parent. The parent may be itself a differencing medium, thus forming a chain of linked media. The last element in that chain must always be a base medium. Note that several differencing media may be linked to the same parent medium.

Differencing media can be distinguished from base media by querying the parent attribute: base media do not have parents they would depend on, so the value of this attribute is always `null` for them. Using this attribute, it is possible to walk up the medium tree (from the child medium to its parent). It is also possible to walk down the tree using the children attribute.

Note that the type of all differencing media is "normal"; all other values are meaningless for them. Base media may be of any type.

### Automatic composition of the file name part

Another extension to the IMedium::location attribute is that there is a possibility to cause VirtualBox to compose a unique value for the file name part of the location using the UUID of the hard disk. This applies only to hard disks in MediumState_NotCreated state, e.g. before the storage unit is created, and works as follows. You set the value of the IMedium::location attribute to a location specification which only contains the path specification but not the file name part and ends with either a forward slash or a backslash character. In response, VirtualBox will generate a new UUID for the hard disk and compose the file name using the following pattern:

            <path>/{<uuid>}.<ext>

where `<path>` is the supplied path specification, `<uuid>` is the newly generated UUID and `<ext>` is the default extension for the storage format of this hard disk. After that, you may call any of the methods that create a new hard disk storage unit and they will use the generated UUID and file name.

Interface ID:
  `{AD47AD09-787B-44AB-B343-A082A3F2DFB1}`

## Member Function Documentation

## ◆ setIds()

void IMedium::setIds | ( | in boolean | setImageId,
|  | in wstringUUID | imageId,
|  | in boolean | setParentId,
|  | in wstringUUID | parentId
| ) |  |

Changes the UUID and parent UUID for a hard disk medium.

Parameters

  setImageId | Select whether a new image UUID is set or not.
  imageId | New UUID for the image. If an empty string is passed, then a new UUID is automatically created, provided that setImageId is `true`. Specifying a zero UUID is not allowed.
  setParentId | Select whether a new parent UUID is set or not.
  parentId | New parent UUID for the image. If an empty string is passed, then a new UUID is automatically created, provided setParentId is `true`. A zero UUID is valid.

## ◆ refreshState()

void IMedium::refreshState | ( | [retval] out MediumState | state | ) |

If the current medium state (see MediumState) is one of "Created", "Inaccessible" or "LockedRead", then this performs an accessibility check on the medium and sets the value of the state attribute accordingly; that value is also returned for convenience.

For all other state values, this does not perform a refresh but returns the state only.

The refresh, if performed, may take a long time (several seconds or even minutes, depending on the storage unit location and format) because it performs an accessibility check of the storage unit. This check may cause a significant delay if the storage unit of the given medium is, for example, a file located on a network share which is not currently accessible due to connectivity problems. In that case, the call will not return until a timeout interval defined by the host OS for this operation expires. For this reason, it is recommended to never read this attribute on the main UI thread to avoid making the UI unresponsive.

If the last known state of the medium is "Created" and the accessibility check fails, then the state would be set to "Inaccessible", and lastAccessError may be used to get more details about the failure. If the state of the medium is "LockedRead", then it remains the same, and a non-empty value of lastAccessError will indicate a failed accessibility check in this case.

Note that not all medium states are applicable to all medium types.

Parameters

  state | New medium state.

## ◆ getSnapshotIds()

void IMedium::getSnapshotIds | ( | in wstringUUID | machineId,
|  | [retval] out wstringUUID[] | snapshotIds
| ) |  |

Returns an array of UUIDs of all snapshots of the given machine where this medium is attached to.

If the medium is attached to the machine in the current state, then the first element in the array will always be the ID of the queried machine (i.e. the value equal to the `machineId` argument), followed by snapshot IDs (if any).

If the medium is not attached to the machine in the current state, then the array will contain only snapshot IDs.

The returned array may be `null` if this medium is not attached to the given machine at all, neither in the current state nor in one of the snapshots.

Parameters

  machineId | UUID of the machine to query.
  snapshotIds | Array of snapshot UUIDs of the given machine using this medium.

## ◆ lockRead()

void IMedium::lockRead | ( | [retval] out IToken | token | ) |

Locks this medium for reading.

A read lock is shared: many clients can simultaneously lock the same medium for reading unless it is already locked for writing (see lockWrite) in which case an error is returned.

When the medium is locked for reading, it cannot be modified from within VirtualBox. This means that any method that changes the properties of this medium or contents of the storage unit will return an error (unless explicitly stated otherwise). That includes an attempt to start a virtual machine that wants to write to the medium.

When the virtual machine is started up, it locks for reading all media it uses in read-only mode. If some medium cannot be locked for reading, the startup procedure will fail. A medium is typically locked for reading while it is used by a running virtual machine but has a depending differencing image that receives the actual write operations. This way one base medium can have multiple child differencing images which can be written to simultaneously. Read-only media such as DVD and floppy images are also locked for reading only (so they can be in use by multiple machines simultaneously).

A medium is also locked for reading when it is the source of a write operation such as cloneTo or mergeTo.

The medium locked for reading must be unlocked by abandoning the returned token object, see IToken. Calls to lockRead can be nested and the lock is actually released when all callers have abandoned the token.

This method sets the medium state (see state) to "LockedRead" on success. The medium's previous state must be one of "Created", "Inaccessible" or "LockedRead".

Locking an inaccessible medium is not an error; this method performs a logical lock that prevents modifications of this medium through the VirtualBox API, not a physical file-system lock of the underlying storage unit.

This method returns the current state of the medium before the operation.

Parameters

  token | Token object, when this is released (reference count reaches 0) then the lock count is decreased. The lock is released when the lock count reaches 0.

Expected result codes:

  VBOX_E_INVALID_OBJECT_STATE | Invalid medium state (e.g. not created, locked, inaccessible, creating, deleting).

## ◆ lockWrite()

void IMedium::lockWrite | ( | [retval] out IToken | token | ) |

Locks this medium for writing.

A write lock, as opposed to lockRead, is exclusive: there may be only one client holding a write lock, and there may be no read locks while the write lock is held. As a result, read-locking fails if a write lock is held, and write-locking fails if either a read or another write lock is held.

When a medium is locked for writing, it cannot be modified from within VirtualBox, and it is not guaranteed that the values of its properties are up-to-date. Any method that changes the properties of this medium or contents of the storage unit will return an error (unless explicitly stated otherwise).

When a virtual machine is started up, it locks for writing all media it uses to write data to. If any medium could not be locked for writing, the startup procedure will fail. If a medium has differencing images, then while the machine is running, only the last ("leaf") differencing image is locked for writing, whereas its parents are locked for reading only.

A medium is also locked for writing when it is the target of a write operation such as cloneTo or mergeTo.

The medium locked for writing must be unlocked by abandoning the returned token object, see IToken. Write locks cannot be nested.

This method sets the medium state (see state) to "LockedWrite" on success. The medium's previous state must be either "Created" or "Inaccessible".

Locking an inaccessible medium is not an error; this method performs a logical lock that prevents modifications of this medium through the VirtualBox API, not a physical file-system lock of the underlying storage unit.

Parameters

  token | Token object, when this is released (reference count reaches 0) then the lock is released.

Expected result codes:

  VBOX_E_INVALID_OBJECT_STATE | Invalid medium state (e.g. not created, locked, inaccessible, creating, deleting).

## ◆ close()

void IMedium::close | ( |  | ) |

Closes this medium.

The medium must not be attached to any known virtual machine and must not have any known child media, otherwise the operation will fail.

When the medium is successfully closed, it is removed from the list of registered media, but its storage unit is not deleted. In particular, this means that this medium can later be opened again using the IVirtualBox::openMedium call.

Note that after this method successfully returns, the given medium object becomes uninitialized. This means that any attempt to call any of its methods or attributes will fail with the `"Object not ready" (E_ACCESSDENIED)` error.

Expected result codes:

  VBOX_E_INVALID_OBJECT_STATE | Invalid medium state (other than not created, created or inaccessible).
  VBOX_E_OBJECT_IN_USE | Medium attached to virtual machine.
  VBOX_E_FILE_ERROR | Settings file not accessible.
  VBOX_E_XML_ERROR | Could not parse the settings file.

## ◆ getProperty()

void IMedium::getProperty | ( | in wstring | name,
|  | [retval] out wstring | value
| ) |  |

Returns the value of the custom medium property with the given name.

The list of all properties supported by the given medium format can be obtained with IMediumFormat::describeProperties.

Parameters

  name | Name of the property to get.
  value | Current property value.

Expected result codes:

  VBOX_E_OBJECT_NOT_FOUND | Requested property does not exist (not supported by the format).
  E_INVALIDARG | name is `null` or empty.

Note
  If this method returns an empty string in value, the requested property is supported but currently not assigned any value.

## ◆ setProperty()

void IMedium::setProperty | ( | in wstring | name,
|  | in wstring | value
| ) |  |

Sets the value of the custom medium property with the given name.

The list of all properties supported by the given medium format can be obtained with IMediumFormat::describeProperties.

Parameters

  name | Name of the property to set.
  value | Property value to set.

Expected result codes:

  VBOX_E_OBJECT_NOT_FOUND | Requested property does not exist (not supported by the format).
  E_INVALIDARG | name is `null` or empty.

Note
  Setting the property value to `null` or an empty string is equivalent to deleting the existing value. A default value (if it is defined for this property) will be used by the format backend in this case.

## ◆ getProperties()

void IMedium::getProperties | ( | in wstring | names,
|  | out wstring[] | returnNames,
|  | [retval] out wstring[] | returnValues
| ) |  |

Returns values for a group of properties in one call.

The names of the properties to get are specified using the names argument which is a list of comma-separated property names or an empty string if all properties are to be returned.

The list of all properties supported by the given medium format can be obtained with IMediumFormat::describeProperties.

The method returns two arrays, the array of property names corresponding to the names argument and the current values of these properties. Both arrays have the same number of elements with each element at the given index in the first array corresponds to an element at the same index in the second array.

For properties that do not have assigned values, an empty string is returned at the appropriate index in the returnValues array.

Parameters

  names | Names of properties to get.
  returnNames | Names of returned properties.
  returnValues | Values of returned properties.

Note
  Currently the value of this argument is ignored and the method always returns all existing properties.

## ◆ setProperties()

void IMedium::setProperties | ( | in wstring[] | names,
|  | in wstring[] | values
| ) |  |

Sets values for a group of properties in one call.

The names of the properties to set are passed in the names array along with the new values for them in the values array. Both arrays have the same number of elements with each element at the given index in the first array corresponding to an element at the same index in the second array.

If there is at least one property name in names that is not valid, the method will fail before changing the values of any other properties from the names array.

Using this method over setProperty is preferred if you need to set several properties at once since it is more efficient.

The list of all properties supported by the given medium format can be obtained with IMediumFormat::describeProperties.

Setting the property value to `null` or an empty string is equivalent to deleting the existing value. A default value (if it is defined for this property) will be used by the format backend in this case.

Parameters

  names | Names of properties to set.
  values | Values of properties to set.

## ◆ createBaseStorage()

void IMedium::createBaseStorage | ( | in long long | logicalSize,
|  | in MediumVariant[] | variant,
|  | [retval] out IProgress | progress
| ) |  |

Starts creating a hard disk storage unit (fixed/dynamic, according to the variant flags) in the background.

The previous storage unit created for this object, if any, must first be deleted using deleteStorage, otherwise the operation will fail.

Before the operation starts, the medium is placed in MediumState_Creating state. If the create operation fails, the medium will be placed back in MediumState_NotCreated state.

After the returned progress object reports that the operation has successfully completed, the medium state will be set to MediumState_Created, the medium will be remembered by this VirtualBox installation and may be attached to virtual machines.

Parameters

  logicalSize | Maximum logical size of the medium in bytes.
  variant | Exact image variant which should be created (as a combination of MediumVariant flags).
  progress | Progress object to track the operation completion.

Expected result codes:

  VBOX_E_NOT_SUPPORTED | The variant of storage creation operation is not supported. See IMediumFormat::capabilities.

## ◆ deleteStorage()

void IMedium::deleteStorage | ( | [retval] out IProgress | progress | ) |

Starts deleting the storage unit of this medium.

The medium must not be attached to any known virtual machine and must not have any known child media, otherwise the operation will fail. It will also fail if there is no storage unit to delete or if deletion is already in progress, or if the medium is being in use (locked for read or for write) or inaccessible. Therefore, the only valid state for this operation to succeed is MediumState_Created.

Before the operation starts, the medium is placed in MediumState_Deleting state and gets removed from the list of remembered hard disks (media registry). If the delete operation fails, the medium will be remembered again and placed back to MediumState_Created state.

After the returned progress object reports that the operation is complete, the medium state will be set to MediumState_NotCreated and you will be able to use one of the storage creation methods to create it again.

Parameters

  progress | Progress object to track the operation completion.

Expected result codes:

  VBOX_E_OBJECT_IN_USE | Medium is attached to a virtual machine.
  VBOX_E_NOT_SUPPORTED | Storage deletion is not allowed because neither of storage creation operations are supported. See IMediumFormat::capabilities.

Note
  If the deletion operation fails, it is not guaranteed that the storage unit still exists. You may check the IMedium::state value to answer this question.

See also
  close

## ◆ createDiffStorage()

void IMedium::createDiffStorage | ( | in IMedium | target,
|  | in MediumVariant[] | variant,
|  | [retval] out IProgress | progress
| ) |  |

Starts creating an empty differencing storage unit based on this medium in the format and at the location defined by the target argument.

The target medium must be in MediumState_NotCreated state (i.e. must not have an existing storage unit). Upon successful completion, this operation will set the type of the target medium to MediumType_Normal and create a storage unit necessary to represent the differencing medium data in the given format (according to the storage format of the target object).

After the returned progress object reports that the operation is successfully complete, the target medium gets remembered by this VirtualBox installation and may be attached to virtual machines.

Parameters

  target | Target medium.
  variant | Exact image variant which should be created (as a combination of MediumVariant flags).
  progress | Progress object to track the operation completion.

Expected result codes:

  VBOX_E_OBJECT_IN_USE | Medium not in `NotCreated` state.

Note
  The medium will be set to MediumState_LockedRead state for the duration of this operation.

## ◆ mergeTo()

void IMedium::mergeTo | ( | in IMedium | target,
|  | [retval] out IProgress | progress
| ) |  |

Starts merging the contents of this medium and all intermediate differencing media in the chain to the given target medium.

The target medium must be either a descendant of this medium or its ancestor (otherwise this method will immediately return a failure). It follows that there are two logical directions of the merge operation: from ancestor to descendant (forward merge) and from descendant to ancestor (backward merge). Let us consider the following medium chain:

    Base <- Diff_1 <- Diff_2

Here, calling this method on the `Base` medium object with `Diff_2` as an argument will be a forward merge; calling it on `Diff_2` with `Base` as an argument will be a backward merge. Note that in both cases the contents of the resulting medium will be the same, the only difference is the medium object that takes the result of the merge operation. In case of the forward merge in the above example, the result will be written to `Diff_2`; in case of the backward merge, the result will be written to `Base`. In other words, the result of the operation is always stored in the target medium.

Upon successful operation completion, the storage units of all media in the chain between this (source) medium and the target medium, including the source medium itself, will be automatically deleted and the relevant medium objects (including this medium) will become uninitialized. This means that any attempt to call any of their methods or attributes will fail with the `"Object not ready" (E_ACCESSDENIED)` error. Applied to the above example, the forward merge of `Base` to `Diff_2` will delete and uninitialize both `Base` and `Diff_1` media. Note that `Diff_2` in this case will become a base medium itself since it will no longer be based on any other medium.

Considering the above, all of the following conditions must be met in order for the merge operation to succeed:

- Neither this (source) medium nor any intermediate differencing medium in the chain between it and the target medium is attached to any virtual machine.
- Neither the source medium nor the target medium is an MediumType_Immutable medium.
- The part of the medium tree from the source medium to the target medium is a linear chain, i.e. all medium in this chain have exactly one child which is the next medium in this chain. The only exception from this rule is the target medium in the forward merge operation; it is allowed to have any number of child media because the merge operation will not change its logical contents (as it is seen by the guest OS or by children).
- None of the involved media are in MediumState_LockedRead or MediumState_LockedWrite state.

Parameters

  target | Target medium.
  progress | Progress object to track the operation completion.

Note
  This (source) medium and all intermediates will be placed to MediumState_Deleting state and the target medium will be placed to MediumState_LockedWrite state and for the duration of this operation.

## ◆ cloneTo()

void IMedium::cloneTo | ( | in IMedium | target,
|  | in MediumVariant[] | variant,
|  | in IMedium | parent,
|  | [retval] out IProgress | progress
| ) |  |

Starts creating a clone of this medium in the format and at the location defined by the target argument.

The target medium must be either in MediumState_NotCreated state (i.e. must not have an existing storage unit) or in MediumState_Created state (i.e. created and not locked, and big enough to hold the data or else the copy will be partial). Upon successful completion, the cloned medium will contain exactly the same sector data as the medium being cloned, except that in the first case a new UUID for the clone will be randomly generated, and in the second case the UUID will remain unchanged.

The parent argument defines which medium will be the parent of the clone. Passing a `null` reference indicates that the clone will be a base image, i.e. completely independent. It is possible to specify an arbitrary medium for this parameter, including the parent of the medium which is being cloned. Even cloning to a child of the source medium is possible. Note that when cloning to an existing image, the parent argument is ignored.

After the returned progress object reports that the operation is successfully complete, the target medium gets remembered by this VirtualBox installation and may be attached to virtual machines.

Parameters

  target | Target medium.
  variant | Exact image variant which should be created (as a combination of MediumVariant flags).
  parent | Parent of the cloned medium.
  progress | Progress object to track the operation completion.

Expected result codes:

  E_NOTIMPL | The specified cloning variant is not supported at the moment.

Note
  This medium will be placed to MediumState_LockedRead state for the duration of this operation.

## ◆ cloneToBase()

void IMedium::cloneToBase | ( | in IMedium | target,
|  | in MediumVariant[] | variant,
|  | [retval] out IProgress | progress
| ) |  |

Starts creating a clone of this medium in the format and at the location defined by the target argument.

The target medium must be either in MediumState_NotCreated state (i.e. must not have an existing storage unit) or in MediumState_Created state (i.e. created and not locked, and big enough to hold the data or else the copy will be partial). Upon successful completion, the cloned medium will contain exactly the same sector data as the medium being cloned, except that in the first case a new UUID for the clone will be randomly generated, and in the second case the UUID will remain unchanged.

The parent argument defines which medium will be the parent of the clone. In this case the clone will be a base image, i.e. completely independent. It is possible to specify an arbitrary medium for this parameter, including the parent of the medium which is being cloned. Even cloning to a child of the source medium is possible. Note that when cloning to an existing image, the parent argument is ignored.

After the returned progress object reports that the operation is successfully complete, the target medium gets remembered by this VirtualBox installation and may be attached to virtual machines.

Parameters

  target | Target medium.
  variant | MediumVariant flags).
  progress | Progress object to track the operation completion.

Expected result codes:

  E_NOTIMPL | The specified cloning variant is not supported at the moment.

Note
  This medium will be placed to MediumState_LockedRead state for the duration of this operation.

## ◆ moveTo()

void IMedium::moveTo | ( | in wstring | location,
|  | [retval] out IProgress | progress
| ) |  |

Changes the location of this medium.

Some medium types may support changing the storage unit location by simply changing the value of the associated property. In this case the operation is performed immediately, and progress is returning a `null` reference. Otherwise on success there is a progress object returned, which signals progress and completion of the operation. This distinction is necessary because for some formats the operation is very fast, while for others it can be very slow (moving the image file by copying all data), and in the former case it'd be a waste of resources to create a progress object which will immediately signal completion.

When setting a location for a medium which corresponds to a/several regular file(s) in the host's file system, the given file name may be either relative to the VirtualBox home folder or absolute. Note that if the given location specification does not contain the file extension part then a proper default extension will be automatically appended by the implementation depending on the medium type.

Parameters

  location | New location.
  progress | Progress object to track the operation completion.

Expected result codes:

  E_NOTIMPL | The operation is not implemented yet.
  VBOX_E_NOT_SUPPORTED | Medium format does not support changing the location.

## ◆ compact()

void IMedium::compact | ( | [retval] out IProgress | progress | ) |

Starts compacting of this medium.

This means that the medium is transformed into a possibly more compact storage representation. This potentially creates temporary images, which can require a substantial amount of additional disk space.

This medium will be placed to MediumState_LockedWrite state and all its parent media (if any) will be placed to MediumState_LockedRead state for the duration of this operation.

Please note that the results can be either returned straight away, or later as the result of the background operation via the object returned via the progress parameter.

Parameters

  progress | Progress object to track the operation completion.

Expected result codes:

  VBOX_E_NOT_SUPPORTED | Medium format does not support compacting (but potentially needs it).

## ◆ resize()

void IMedium::resize | ( | in long long | logicalSize,
|  | [retval] out IProgress | progress
| ) |  |

Starts resizing this medium.

This means that the nominal size of the medium is set to the new value. Both increasing and decreasing the size is possible, and there are no safety checks, since VirtualBox does not make any assumptions about the medium contents.

Resizing usually needs additional disk space, and possibly also some temporary disk space. Note that resize does not create a full temporary copy of the medium, so the additional disk space requirement is usually much lower than using the clone operation.

This medium will be placed to MediumState_LockedWrite state for the duration of this operation.

Please note that the results can be either returned straight away, or later as the result of the background operation via the object returned via the progress parameter.

Parameters

  logicalSize | New nominal capacity of the medium in bytes.
  progress | Progress object to track the operation completion.

Expected result codes:

  VBOX_E_NOT_SUPPORTED | Medium format does not support resizing.

## ◆ reset()

void IMedium::reset | ( | [retval] out IProgress | progress | ) |

Starts erasing the contents of this differencing medium.

This operation will reset the differencing medium to its initial state when it does not contain any sector data and any read operation is redirected to its parent medium. This automatically gets called during VM power-up for every medium whose autoReset attribute is `true`.

The medium will be write-locked for the duration of this operation (see lockWrite).

Parameters

  progress | Progress object to track the operation completion.

Expected result codes:

  VBOX_E_NOT_SUPPORTED | This is not a differencing medium.
  VBOX_E_INVALID_OBJECT_STATE | Medium is not in MediumState_Created or MediumState_Inaccessible state.

## ◆ changeEncryption()

void IMedium::changeEncryption | ( | in wstring | currentPassword,
|  | in wstring | cipher,
|  | in wstring | newPassword,
|  | in wstring | newPasswordId,
|  | [retval] out IProgress | progress
| ) |  |

Starts encryption of this medium.

This means that the stored data in the medium is encrypted.

This medium will be placed to MediumState_LockedWrite state.

Please note that the results can be either returned straight away, or later as the result of the background operation via the object returned via the progress parameter.

Parameters

  currentPassword | The current password the medium is protected with. Use an empty string to indicate that the medium isn't encrypted.
  cipher | The cipher to use for encryption. An empty string indicates no encryption for the result.
  newPassword | The new password the medium should be protected with. An empty password and password ID will result in the medium being encrypted with the current password.
  newPasswordId | The ID of the new password when unlocking the medium.
  progress | Progress object to track the operation completion.

Expected result codes:

  VBOX_E_NOT_SUPPORTED | Encryption is not supported for this medium because it is attached to more than one VM or has children.

## ◆ getEncryptionSettings()

void IMedium::getEncryptionSettings | ( | out wstring | cipher,
|  | [retval] out wstring | passwordId
| ) |  |

Returns the encryption settings for this medium.

Parameters

  cipher | The cipher used for encryption.
  passwordId | The ID of the password when unlocking the medium.

Expected result codes:

  VBOX_E_NOT_SUPPORTED | Encryption is not configured for this medium.

## ◆ checkEncryptionPassword()

void IMedium::checkEncryptionPassword | ( | in wstring | password | ) |

Checks whether the supplied password is correct for the medium.

Parameters

  password | The password to check.

Expected result codes:

  VBOX_E_NOT_SUPPORTED | Encryption is not configured for this medium.
  VBOX_E_PASSWORD_INCORRECT | The given password is incorrect.

## ◆ openForIO()

void IMedium::openForIO | ( | in boolean | writable,
|  | in wstring | password,
|  | [retval] out IMediumIO | mediumIO
| ) |  |

Open the medium for I/O.

Parameters

  writable | Set this to open the medium for both reading and writing. When not set the medium is opened readonly.
  password | Password for accessing an encrypted medium. Must be empty if not encrypted.
  mediumIO | Medium I/O object.

## ◆ resizeAndCloneTo()

void IMedium::resizeAndCloneTo | ( | in IMedium | target,
|  | in long long | logicalSize,
|  | in MediumVariant[] | variant,
|  | in IMedium | parent,
|  | [retval] out IProgress | progress
| ) |  |

This is a helper function that combines the functionality of IMedium::cloneTo and IMedium::resize.

The target medium will take the contents of the calling medium.

Parameters

  target | Target medium.
  logicalSize | New nominal capacity of the medium in bytes.
  variant | Exact image variant which should be created (as a combination of MediumVariant flags).
  parent | Parent of the cloned medium.
  progress | Progress object to track the operation completion.

Expected result codes:

  E_NOTIMPL | The specified cloning variant is not supported at the moment.

Note
  Method will be moved to appropriate location at the next major API release.

## Member Data Documentation

## ◆ id

readonly attribute wstringUUID IMedium::id

UUID of the medium.

For a newly created medium, this value is a randomly generated UUID.

Note
  For media in one of MediumState_NotCreated, MediumState_Creating or MediumState_Deleting states, the value of this property is undefined and will most likely be an empty UUID.

## ◆ description

attribute wstring IMedium::description

Optional description of the medium.

For a newly created medium the value of this attribute is an empty string.

Medium types that don't support this attribute will return E_NOTIMPL in attempt to get or set this attribute's value.

Note
  For some storage types, reading this attribute may return an outdated (last known) value when state is MediumState_Inaccessible or MediumState_LockedWrite because the value of this attribute is stored within the storage unit itself. Also note that changing the attribute value is not possible in such case, as well as when the medium is the MediumState_LockedRead state.

## ◆ state

readonly attribute MediumState IMedium::state

Returns the current medium state, which is the last state set by the accessibility check performed by refreshState.

If that method has not yet been called on the medium, the state is "Inaccessible"; as opposed to truly inaccessible media, the value of lastAccessError will be an empty string in that case.

Note
  As of version 3.1, this no longer performs an accessibility check automatically; call refreshState for that.

## ◆ variant

readonly attribute MediumVariant [] IMedium::variant

Returns the storage format variant information for this medium as an array of the flags described at MediumVariant.

Before refreshState is called this method returns an undefined value.

## ◆ location

attribute wstring IMedium::location

Location of the storage unit holding medium data.

The format of the location string is medium type specific. For medium types using regular files in a host's file system, the location string is the full file name.

## ◆ name

readonly attribute wstring IMedium::name

Name of the storage unit holding medium data.

The returned string is a short version of the location attribute that is suitable for representing the medium in situations where the full location specification is too long (such as lists and comboboxes in GUI frontends). This string is also used by frontends to sort the media list alphabetically when needed.

For example, for locations that are regular files in the host's file system, the value of this attribute is just the file name (+ extension), without the path specification.

Note that as opposed to the location attribute, the name attribute will not necessary be unique for a list of media of the given type and format.

## ◆ deviceType

readonly attribute DeviceType IMedium::deviceType

Kind of device (DVD/Floppy/HardDisk) which is applicable to this medium.

## ◆ hostDrive

readonly attribute boolean IMedium::hostDrive

True if this corresponds to a drive on the host.

## ◆ size

readonly attribute long long IMedium::size

Physical size of the storage unit used to hold medium data (in bytes).

Note
  For media whose state is MediumState_Inaccessible, the value of this property is the last known size. For MediumState_NotCreated media, the returned value is zero.

## ◆ format

readonly attribute wstring IMedium::format

Storage format of this medium.

The value of this attribute is a string that specifies a backend used to store medium data. The storage format is defined when you create a new medium or automatically detected when you open an existing medium, and cannot be changed later.

The list of all storage formats supported by this VirtualBox installation can be obtained using ISystemProperties::mediumFormats.

## ◆ mediumFormat

readonly attribute IMediumFormat IMedium::mediumFormat

Storage medium format object corresponding to this medium.

The value of this attribute is a reference to the medium format object that specifies the backend properties used to store medium data. The storage format is defined when you create a new medium or automatically detected when you open an existing medium, and cannot be changed later.

Note
  `null` is returned if there is no associated medium format object. This can e.g. happen for medium objects representing host drives and other special medium objects.

## ◆ type

attribute MediumType IMedium::type

Type (role) of this medium.

The following constraints apply when changing the value of this attribute:

- If a medium is attached to a virtual machine (either in the current state or in one of the snapshots), its type cannot be changed.
- As long as the medium has children, its type cannot be set to MediumType_Writethrough.
- The type of all differencing media is MediumType_Normal and cannot be changed.

The type of a newly created or opened medium is set to MediumType_Normal, except for DVD and floppy media, which have a type of MediumType_Writethrough.

## ◆ allowedTypes

readonly attribute MediumType [] IMedium::allowedTypes

Returns which medium types can selected for this medium.

Expected result codes:

  E_NOTIMPL | This attribute is not implemented at the moment.

## ◆ parent

readonly attribute IMedium IMedium::parent

Parent of this medium (the medium this medium is directly based on).

Only differencing media have parents. For base (non-differencing) media, `null` is returned.

## ◆ children

readonly attribute IMedium [] IMedium::children

Children of this medium (all differencing media directly based on this medium).

A `null` array is returned if this medium does not have any children.

## ◆ base

readonly attribute IMedium IMedium::base

Base medium of this medium.

If this is a differencing medium, its base medium is the medium the given medium branch starts from. For all other types of media, this property returns the medium object itself (i.e. the same object this property is read on).

## ◆ readOnly

readonly attribute boolean IMedium::readOnly

Returns `true` if this medium is read-only and `false` otherwise.

A medium is considered to be read-only when its contents cannot be modified without breaking the integrity of other parties that depend on this medium such as its child media or snapshots of virtual machines where this medium is attached to these machines. If there are no children and no such snapshots then there is no dependency and the medium is not read-only.

The value of this attribute can be used to determine the kind of the attachment that will take place when attaching this medium to a virtual machine. If the value is `false` then the medium will be attached directly. If the value is `true` then the medium will be attached indirectly by creating a new differencing child medium for that. See the interface description for more information.

Note that all Immutable media are always read-only while all Writethrough media are always not.

Note
  The read-only condition represented by this attribute is related to the medium type and usage, not to the current medium state and not to the read-only state of the storage unit.

## ◆ logicalSize

readonly attribute long long IMedium::logicalSize

Logical size of this medium (in bytes), as reported to the guest OS running inside the virtual machine this medium is attached to.

The logical size is defined when the medium is created and cannot be changed later.

Note
  For media whose state is state is MediumState_Inaccessible, the value of this property is the last known logical size. For MediumState_NotCreated media, the returned value is zero.

## ◆ autoReset

attribute boolean IMedium::autoReset

Whether this differencing medium will be automatically reset each time a virtual machine it is attached to is powered up.

This attribute is automatically set to `true` for the last differencing image of an "immutable" medium (see MediumType).

See reset for more information about resetting differencing media.

Expected result codes:

  VBOX_E_NOT_SUPPORTED | This is not a differencing medium (when changing the attribute value).

Note
  Reading this property on a base (non-differencing) medium will always `false`. Changing the value of this property in this case is not supported.

## ◆ lastAccessError

readonly attribute wstring IMedium::lastAccessError

Text message that represents the result of the last accessibility check performed by refreshState.

An empty string is returned if the last accessibility check was successful or has not yet been called. As a result, if state is "Inaccessible" and this attribute is empty, then refreshState has yet to be called; this is the default value of media after VirtualBox initialization. A non-empty string indicates a failure and should normally describe a reason of the failure (for example, a file read error).

## ◆ machineIds

readonly attribute wstringUUID [] IMedium::machineIds

Array of UUIDs of all machines this medium is attached to.

A `null` array is returned if this medium is not attached to any machine or to any machine's snapshot.

Note
  The returned array will include a machine even if this medium is not attached to that machine in the current state but attached to it in one of the machine's snapshots. See getSnapshotIds for details.