Saving my read_usn method in case I want it later

read_usn.c

// FILE_ID.Identifier is BYTE[16] containing a single 128-bit unsigned integer
static PyObject *
_PyLong_From_FILE_ID(FILE_ID_128 *id)
{
    PyObject *low = PyLong_FromUnsignedLongLong(
        *(unsigned long long*)&id->Identifier[0]
    );
    if (!low) {
        return NULL;
    }
    PyObject *number = PyLong_FromUnsignedLongLong(
        *(unsigned long long*)&id->Identifier[8]
    );
    if (number) {
        Py_SETREF(number, _PyLong_Lshift(number, 64));
    }
    if (number) {
        Py_SETREF(number, _PyLong_Add((PyLongObject *)number, (PyLongObject *)low));
    }
    Py_DECREF(low);
    return number;
}


/*[clinic input]
_winapi.read_usn

    path: LPCWSTR

Efficiently reads the USN number for the specified path.
[clinic start generated code]*/

static PyObject *
_winapi_read_usn_impl(PyObject *module, LPCWSTR path)
/*[clinic end generated code: output=9a744a78b72e3fcf input=cfcf31cb44d0a9c7]*/
{
    HANDLE hFile;
    int err = 0;
    union {
        unsigned char buffer[32678];
        USN_RECORD_COMMON_HEADER hdr;
        USN_RECORD_V2 v2;
        USN_RECORD_V3 v3;
        USN_RECORD_V4 v4;
    } usn;

    memset(&usn.hdr, 0, sizeof(usn.hdr));
    Py_BEGIN_ALLOW_THREADS;
    hFile = CreateFileW(
        path,
        FILE_READ_ATTRIBUTES,
        FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
        NULL,
        OPEN_EXISTING,
        0,
        NULL
    );
    if (hFile != INVALID_HANDLE_VALUE) {
        DWORD bytesReturned = 0;
        if (!DeviceIoControl(
            hFile,
            FSCTL_READ_FILE_USN_DATA,
            NULL, 0, // no input data
            usn.buffer, sizeof(usn), // output data
            &bytesReturned,
            NULL
        )) {
            err = GetLastError();
        }
        CloseHandle(hFile);
    } else {
        err = GetLastError();
    }
    Py_END_ALLOW_THREADS;

    if (err) {
        PyErr_SetFromWindowsErr(err);
        return NULL;
    }

    PyObject *number = NULL;
    if (usn.hdr.MajorVersion == 2) {
        number = PyLong_FromUnsignedLongLong(usn.v2.FileReferenceNumber);
    } else if (usn.hdr.MajorVersion == 3) {
        number = _PyLong_From_FILE_ID(&usn.v3.FileReferenceNumber);
    } else if (usn.hdr.MajorVersion == 4) {
        number = _PyLong_From_FILE_ID(&usn.v4.FileReferenceNumber);
    } else {
        number = Py_None;
        Py_INCREF(number);
    }

    if (!number) {
        return NULL;
    }
    return Py_BuildValue("(hhN)", usn.hdr.MajorVersion, usn.hdr.MinorVersion, number);
}