How to understand the "NTSTATUS", "NT_SUCCESS" typedef in windows ddk?

Question

Two questions:

1.

In "ntdef.h" the NTSTATUS is defined as follow:

typedef __success(return >= 0) LONG NTSTATUS;

what the hell is the "__success(return >= 0)"?

2.

In "ntstatus.h", STATUS_SUCCESS is defined to 0.

#define STATUS_SUCCESS   ((NTSTATUS)0x00000000L) // ntsubauth

But the NT_SUCCESS macro in "ntdef.h" is:

#define NT_SUCCESS(Status) (((NTSTATUS)(Status)) >= 0)

Shouldn't it be "Status == 0" ?

Answer 1

__success is an "Advanced Annotation" defined in SpecStrings_strict.h, which defines it as follows.

*  __success(expr) T f() :  indicates whether function f succeeded or
*  not. If  is true at exit, all the function's guarantees (as given
*  by other annotations) must hold. If  is false at exit, the caller
*  should not expect any of the function's guarantees to hold. If not used,
*  the function must always satisfy its guarantees. Added automatically to
*  functions that indicate success in standard ways, such as by returning an
*  HRESULT.

The reason that NT_SUCCESS doesn't do a strict test against STATUS_SUCCESS (0) is probably that other codes like STATUS_PENDING aren't actually failures.