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FSCTL_DISMOUNT_VOLUME control code

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The FSCTL_DISMOUNT_VOLUME control code attempts to dismount a volume regardless of whether the volume is in use.

To perform this operation, call FltFsControlFile or ZwFsControlFile with the following parameters.

Parameters

  • Instance [in]: FltFsControlFile only. Opaque instance pointer for the caller. This parameter is required and cannot be NULL.

  • FileObject: [in]: FltFsControlFile only. The file pointer object specifying the volume to be dismounted. This parameter is required and cannot be NULL.

  • FileHandle [in]: ZwFsControlFile only. The file handle of the volume to be dismounted. This parameter is required and cannot be NULL.

  • FsControlCode [in]: Control code for the operation. Use FSCTL_DISMOUNT_VOLUME for this operation.

  • InputBuffer [in]: None. Set to NULL.

  • InputBufferLength [in]: Set to 0.

  • OutputBuffer [out]: None. Set to NULL.

  • OutputBufferLength [out]: Set to 0.

Status block

FltFsControlFile or ZwFsControlFile returns STATUS_SUCCESS or an appropriate NTSTATUS value.

Remarks

The FSCTL_DISMOUNT_VOLUME control code will attempt to dismount a volume regardless of whether any other processes are using the volume, which can have unpredictable results for those processes if they do not hold a lock on the volume. For information about locking a volume, see FSCTL_LOCK_VOLUME.

The operating system does not detect unmounted volumes. If an attempt is made to access an unmounted volume, the operating system then tries to mount the volume. For example, a call to GetLogicalDrives triggers the operating system to mount unmounted volumes.

The FileHandle handle passed to ZwFsControlFile must be a handle to a volume, opened for direct access. To retrieve a volume handle, call ZwCreateFile with the ObjectAttributes parameter set to an ObjectName of the following form: \\.\X: where X is a drive letter of the volume, floppy disk drive, or CD-ROM drive. The application must also specify the FILE_SHARE_READ and FILE_SHARE_WRITE flags in the ShareAccess parameter of ZwCreateFile.

If the specified volume is a system volume or contains a page file, the operation fails.

If the specified volume is locked by another process, the operation fails.

Requirements

Requirement type Requirement
Header Ntifs.h (include Ntifs.h or Fltkernel.h)

See also

FltCreateFile

FltFsControlFile

ZwCreateFile

ZwFsControlFile