Many kernel-mode standard driver routines and driver support routines use the NTSTATUS type for return values. Additionally, drivers provide an NTSTATUS-typed value in an IRP's IO_STATUS_BLOCK structure when completing IRPs. The NTSTATUS type is defined in Ntdef.h, and system-supplied status codes are defined in Ntstatus.h. (Vendors can also define private status codes, although they rarely need to. For more information, see Defining New NTSTATUS Values.)
NTSTATUS values are divided into four types: success values, informational values, warnings, and error values.
Numerous values are assigned to each type. A common mistake, when testing for a successful return from a routine, is to compare the routine's return value with STATUS_SUCCESS. This comparison checks for only one of several success values.
When testing a return value, you should use one of the following system-supplied macros (defined in Ntdef.h):
For example, suppose a driver calls IoRegisterDeviceInterface to register a device interface. If the driver checks the return value using the NT_SUCCESS macro, the macro will evaluate to TRUE if the routine returns STATUS_SUCCESS, which indicates no errors, or if it returns the informational status STATUS_OBJECT_NAME_EXISTS, which indicates that the device interface is already registered.
As another example, suppose a driver calls ZwEnumerateKey to enumerate the subkeys of a specified registry key. If the NT_SUCCESS macro evaluates to FALSE, it might be because the routine returned STATUS_INVALID_PARAMETER, which is an error code, or because the routine returned STATUS_NO_MORE_ENTRIES, which is a warning code.
As a final example, suppose a driver sends an IRP that causes a lower-level driver to read information from a device. If the requesting driver specifies a buffer that is too small to receive any information, the lower-level driver might respond by returning STATUS_BUFFER_TOO_SMALL, which is an error code. If the first driver specifies a buffer that can receive some, but not all, of the requested information, the lower-level driver might respond by supplying as much data as possible and then returning STATUS_BUFFER_OVERFLOW, which is a warning code. Note that if the first driver tests the status value using NT_SUCCESS or NT_ERROR incorrectly, it might inadvertently drop some of the information received.