Obtaining Device Configuration Information at IRQL = PASSIVE_LEVEL
To access device configuration space at IRQL = PASSIVE_LEVEL, you must use IRP_MN_READ_CONFIG and IRP_MN_WRITE_CONFIG. You indicate in the IRP stack which configuration space you wish to access and where the I/O buffer is. See the description of the IO_STACK_LOCATION structure for further details.
The following code sample demonstrates how to access a device's configuration space.
NTSTATUS
ReadWriteConfigSpace(
IN PDEVICE_OBJECT DeviceObject,
IN ULONG ReadOrWrite, // 0 for read, 1 for write
IN PVOID Buffer,
IN ULONG Offset,
IN ULONG Length
)
{
KEVENT event;
NTSTATUS status;
PIRP irp;
IO_STATUS_BLOCK ioStatusBlock;
PIO_STACK_LOCATION irpStack;
PDEVICE_OBJECT targetObject;
PAGED_CODE();
KeInitializeEvent(&event, NotificationEvent, FALSE);
targetObject = IoGetAttachedDeviceReference(DeviceObject);
irp = IoBuildSynchronousFsdRequest(IRP_MJ_PNP,
targetObject,
NULL,
0,
NULL,
&event,
&ioStatusBlock);
if (irp == NULL) {
status = STATUS_INSUFFICIENT_RESOURCES;
goto End;
}
irpStack = IoGetNextIrpStackLocation(irp);
if (ReadOrWrite == 0) {
irpStack->MinorFunction = IRP_MN_READ_CONFIG;
} else {
irpStack->MinorFunction = IRP_MN_WRITE_CONFIG;
}
irpStack->Parameters.ReadWriteConfig.WhichSpace = PCI_WHICHSPACE_CONFIG;
irpStack->Parameters.ReadWriteConfig.Buffer = Buffer;
irpStack->Parameters.ReadWriteConfig.Offset = Offset;
irpStack->Parameters.ReadWriteConfig.Length = Length;
// Initialize the status to error in case the bus driver does not
// set it correctly.
irp->IoStatus.Status = STATUS_NOT_SUPPORTED;
status = IoCallDriver(targetObject, irp);
if (status == STATUS_PENDING) {
KeWaitForSingleObject(&event, Executive, KernelMode, FALSE, NULL);
status = ioStatusBlock.Status;
}
End:
// Done with reference
ObDereferenceObject(targetObject);
return status;
}