DeviceIoControl

The DeviceIoControl function sends a control code directly to a specified device driver, causing the corresponding device to perform the specified operation.

BOOL DeviceIoControl(

HANDLE hDevice,	// handle to device of interest
DWORD dwIoControlCode,	// control code of operation to perform
LPVOID lpInBuffer,	// pointer to buffer to supply input data
DWORD nInBufferSize,	// size of input buffer
LPVOID lpOutBuffer,	// pointer to buffer to receive output data
DWORD nOutBufferSize,	// size of output buffer
LPDWORD lpBytesReturned,	// pointer to variable to receive output byte count
LPOVERLAPPED lpOverlapped	// pointer to overlapped structure for asynchronous operation
);

Parameters

hDevice

Handle to the device that is to perform the operation. Call the CreateFile function to obtain a device handle.

dwIoControlCode

Specifies the control code for the operation. This value identifies the specific operation to be performed and the type of device on which the operation is to be performed. The following values are defined:

Value	Meaning
FSCTL_DISMOUNT_VOLUME	Dismounts a volume.
FSCTL_GET_COMPRESSION	Obtains the compression state of a file or directory
FSCTL_LOCK_VOLUME	Locks a volume.
FSCTL_READ_COMPRESSION	Reserved for future use.
FSCTL_SET_COMPRESSION	Sets the compression state of a file or directory.
FSCTL_UNLOCK_VOLUME	Unlocks a volume.
FSCTL_WRITE_COMPRESSION	Reserved for future use.
IOCTL_DISK_CHECK_VERIFY	Obsolete. Use IOCTL_STORAGE_CHECK_VERIFY
IOCTL_DISK_EJECT_MEDIA	Obsolete. Use IOCTL_STORAGE_EJECT_MEDIA
IOCTL_DISK_FORMAT_TRACKS	Formats a contiguous set of disk tracks.
IOCTL_DISK_GET_DRIVE_GEOMETRY	Obtains information on the physical disk's geometry.
IOCTL_DISK_GET_DRIVE_LAYOUT	Provides information about each partition on a disk.
IOCTL_DISK_GET_MEDIA_TYPES	Obsolete. Use IOCTL_STORAGE_GET_MEDIA_TYPES
IOCTL_DISK_GET_PARTITION_INFO	Obtains disk partition information.
IOCTL_DISK_LOAD_MEDIA	Obsolete. Use IOCTL_STORAGE_LOAD_MEDIA
IOCTL_DISK_MEDIA_REMOVAL	Obsolete. Use IOCTL_STORAGE_MEDIA_REMOVAL
IOCTL_DISK_PERFORMANCE	Provides disk performance information.
IOCTL_DISK_REASSIGN_BLOCKS	Maps disk blocks to spare-block pool.
IOCTL_DISK_SET_DRIVE_LAYOUT	Partitions a disk.
IOCTL_DISK_SET_PARTITION_INFO	Sets the disk partition type.
IOCTL_DISK_VERIFY	Performs logical format of a disk extent.
IOCTL_SERIAL_LSRMST_INSERT	Enables or disables placement of a line and modem status data into the data stream.
IOCTL_STORAGE_CHECK_VERIFY	Checks for change in a removable-media device.
IOCTL_STORAGE_EJECT_MEDIA	Ejects media from a SCSI device.
IOCTL_STORAGE_GET_MEDIA_TYPES	Obtains information about media support.
IOCTL_STORAGE_LOAD_MEDIA	Loads media into a device.
IOCTL_STORAGE_MEDIA_REMOVAL	Enables or disables the media eject mechanism.

For more detailed information on each control code, see its topic. In particular, each topic provides details on the usage of the lpInBuffer, nInBufferSize, lpOutBuffer, nOutBufferSize, and lpBytesReturned parameters.

lpInBuffer

Pointer to a buffer that contains the data required to perform the operation.

This parameter can be NULL if the dwIoControlCode parameter specifies an operation that does not require input data.

nInBufferSize

Specifies the size, in bytes, of the buffer pointed to by lpInBuffer.

lpOutBuffer

Pointer to a buffer that receives the operation's output data.

This parameter can be NULL if the dwIoControlCode parameter specifies an operation that does not produce output data.

nOutBufferSize

Specifies the size, in bytes, of the buffer pointed to by lpOutBuffer.

lpBytesReturned

Pointer to a variable that receives the size, in bytes, of the data stored into the buffer pointed to by lpOutBuffer.

If lpOverlapped is NULL, lpBytesReturned cannot be NULL. Even when an operation produces no output data, and lpOutBuffer can be NULL, the DeviceIoControl function makes use of the variable pointed to by lpBytesReturned. After such an operation, the value of the variable is without meaning.

If lpOverlapped is not NULL, lpBytesReturned can be NULL. If this is an overlapped operation, you can get the number of bytes returned by calling GetOverlappedResult. If hDevice is associated with an I/O completion port, you can get the number of bytes returned by calling GetQueuedCompletionStatus.

lpOverlapped

Pointer to an OVERLAPPED structure.

If hDevice was opened with the FILE_FLAG_OVERLAPPED flag, this parameter must point to a valid OVERLAPPED structure. In this case, DeviceIoControl is performed as an overlapped (asynchronous) operation. If the device was opened with FILE_FLAG_OVERLAPPED and lpOverlapped is NULL, the function fails in unpredictable ways.

If hDevice was opened without specifying the FILE_FLAG_OVERLAPPED flag, this parameter is ignored and the DeviceIoControl function does not return until the operation has been completed, or an error occurs.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

If hDevice was opened with FILE_FLAG_OVERLAPPED and the lpOverlapped parameter points to an OVERLAPPED structure, DeviceIoControl is performed as an overlapped (asynchronous) operation. In this case, the OVERLAPPED structure must contain a handle to a manual-reset event object created by a call to the CreateEvent function. For more information on manual-reset event objects, see Synchronization.

If the overlapped operation cannot be completed immediately, the function returns FALSE, and GetLastError returns ERROR_IO_PENDING, indicating that the operation is executing in the background. When this happens, the operating system sets the event object in the OVERLAPPED structure to the nonsignaled state before DeviceIoControl returns. The system then sets the event object to the signaled state when the operation has been completed. The calling thread can use any of the wait functions to wait for the event object to be signaled, and then use the GetOverlappedResult function to determine the results of the operation. The GetOverlappedResult function reports the success or failure of the operation and the number of bytes returned in the lpOutBuffer buffer.

See Also

CreateEvent, CreateFile, GetOverlappedResult, GetQueuedCompletionStatus, OVERLAPPED

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