Descripciones de búfer para códigos de control de E/S

I/O control codes are contained in IRP_MJ_DEVICE_CONTROL and IRP_MJ_INTERNAL_DEVICE_CONTROL requests. The I/O manager creates these requests as a result of calls to DeviceIoControl and IoBuildDeviceIoControlRequest.

Because DeviceIoControl and IoBuildDeviceIoControlRequest accept both an input buffer and an output buffer as arguments, all IRP_MJ_DEVICE_CONTROL and IRP_MJ_INTERNAL_DEVICE_CONTROL requests supply both an input buffer and an output buffer. La forma en que el sistema describe estos búferes depende del tipo de transferencia de datos. The transfer type is specified by the TransferType value in the CTL_CODE macro that creates IOCTL code values.

The system describes buffers for each TransferType value as follows.

METHOD_BUFFERED

For this transfer type, IRPs supply a pointer to a buffer at Irp->AssociatedIrp.SystemBuffer. This buffer represents both the input buffer and the output buffer that are specified in calls to DeviceIoControl and IoBuildDeviceIoControlRequest. El controlador transfiere datos desde este búfer y luego los vuelve a transferir al mismo.

For input data, the buffer size is specified by Parameters.DeviceIoControl.InputBufferLength in the driver's IO_STACK_LOCATION structure. For output data, the buffer size is specified by Parameters.DeviceIoControl.OutputBufferLength in the driver's IO_STACK_LOCATION structure.

El tamaño del espacio que el sistema asigna para el único búfer de entrada y salida es el mayor de los dos valores de longitud.

METHOD_IN_DIRECT o METHOD_OUT_DIRECT

For these transfer types, IRPs supply a pointer to a buffer at Irp->AssociatedIrp.SystemBuffer. This represents the first buffer that is specified in calls to DeviceIoControl and IoBuildDeviceIoControlRequest. The buffer size is specified by Parameters.DeviceIoControl.InputBufferLength in the driver's IO_STACK_LOCATION structure.

For these transfer types, IRPs also supply a pointer to an MDL at Irp->MdlAddress. This represents the second buffer that is specified in calls to DeviceIoControl and IoBuildDeviceIoControlRequest. Este búfer se puede usar como búfer de entrada o como búfer de salida, como se indica a continuación:

• METHOD_IN_DIRECT se especifica si el controlador del IRP recibe datos en el búfer cuando es llamado. MdL describe un búfer de entrada y especificando METHOD_IN_DIRECT garantiza que el subproceso en ejecución tenga acceso de lectura al búfer.

• METHOD_OUT_DIRECT se especifica si el controlador del IRP escribe datos en el búfer antes de completar el IRP. MdL describe un búfer de salida y especificando METHOD_OUT_DIRECT garantiza que el subproceso en ejecución tenga acceso de escritura al búfer.

For both of these transfer types, Parameters.DeviceIoControl.OutputBufferLength specifies the size of the buffer that is described by the MDL.

METHOD_NEITHER

El administrador de E/S no proporciona ningún búfer del sistema ni MDL. The IRP supplies the user-mode virtual addresses of the input and output buffers that were specified to DeviceIoControl or IoBuildDeviceIoControlRequest, without validating or mapping them.

The input buffer's address is supplied by Parameters.DeviceIoControl.Type3InputBuffer in the driver's IO_STACK_LOCATION structure, and the output buffer's address is specified by Irp->UserBuffer.

Buffer sizes are supplied by Parameters.DeviceIoControl.InputBufferLength and Parameters.DeviceIoControl.OutputBufferLength in the driver's IO_STACK_LOCATION structure.

For more information about the CTL_CODE macro and the transfer types listed above, see Defining I/O Control Codes.