Descrições de buffer para códigos de controle 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. A maneira como o sistema descreve esses buffers depende do tipo de transferência de dados. 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. O driver transfere dados para fora deste buffer e, em seguida, para dentro dele novamente.

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.

O tamanho do espaço que o sistema aloca para o buffer de entrada/saída único é o maior dos dois valores de comprimento.

METHOD_IN_DIRECT ou 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. Esse buffer pode ser usado como um buffer de entrada ou um buffer de saída, da seguinte maneira:

• METHOD_IN_DIRECT é especificado se o driver que manipula o IRP recebe dados no buffer quando o driver é chamado. O MDL descreve um buffer de entrada e especificar METHOD_IN_DIRECT garante que o thread em execução tenha acesso de leitura ao buffer.

• O METHOD_OUT_DIRECT é especificado se o driver que manipula o IRP gravar dados no buffer antes de concluir o IRP. O MDL descreve um buffer de saída e especificar METHOD_OUT_DIRECT garante que o thread em execução tenha acesso de gravação ao buffer.

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

METHOD_NEITHER

O gerenciador de E/S não fornece buffers ou MDLs do sistema. 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.