/*++

Copyright (c) 1992-1997  Microsoft Corporation

Module Name:

    uptime.c

Abstract:

    Contains routines to calculate sysUpTime.

        SnmpSvcInitUptime
        SnmpSvcGetUptime
        SnmpSvcGetUptimeFromTime

Environment:

    User Mode - Win32

Revision History:

--*/

///////////////////////////////////////////////////////////////////////////////
//                                                                           //
// Include files                                                             //
//                                                                           //
///////////////////////////////////////////////////////////////////////////////

#include <nt.h>
#include <windef.h>
#include <ntrtl.h>
#include <nturtl.h>
#include <windows.h>
#include <snmp.h>
#include <snmputil.h>
#include <ntfuncs.h>


///////////////////////////////////////////////////////////////////////////////
//                                                                           //
// Global Variables                                                          //
//                                                                           //
///////////////////////////////////////////////////////////////////////////////

DWORD g_dwUpTimeReference = 0;
LONGLONG g_llUpTimeReference = 0;



///////////////////////////////////////////////////////////////////////////////
//                                                                           //
// Private Definitions                                                       //
//                                                                           //
///////////////////////////////////////////////////////////////////////////////

#define INVALID_UPTIME  0xFFFFFFFF


///////////////////////////////////////////////////////////////////////////////
//                                                                           //
// Private Procedures                                                        //
//                                                                           //
///////////////////////////////////////////////////////////////////////////////

DWORD
SNMP_FUNC_TYPE 
SnmpSvcInitUptime(
    )

/*++

Routine Description:

    Initializes sysUpTime reference for SNMP process.

Arguments:

    None.

Return Values:

    Returns sysUpTime reference to pass to subagents. 

--*/

{
    NTSTATUS NtStatus;
    SYSTEM_TIMEOFDAY_INFORMATION TimeOfDay;

    // obtain reference the outdated way
    g_dwUpTimeReference = GetCurrentTime();


    // query time in spiffy new precise manner        
    NtStatus = NtQuerySystemInformation(
                        SystemTimeOfDayInformation,
                        &TimeOfDay,
                        sizeof(SYSTEM_TIMEOFDAY_INFORMATION),
                        NULL
                        );
        
    // validate return code
    if (NT_SUCCESS(NtStatus)) {

        // initialize higher precision startup time         
        g_llUpTimeReference = TimeOfDay.CurrentTime.QuadPart;
    }
    

    //
    // The algorithm for subagents to calculate sysUpTime
    // is based on GetCurrentTime() which returns the time 
    // in milliseconds and therefore wraps every 49.71 days.
    // RFC1213 specifies that sysUpTime is to be returned in
    // centaseconds but we cannot break existing subagents.
    // The old value is returned to the master agent here 
    // but newer subagents should use SnmpUtilGetUpTime.
    //

    return g_dwUpTimeReference;
} 


///////////////////////////////////////////////////////////////////////////////
//                                                                           //
// Public Procedures                                                         //
//                                                                           //
///////////////////////////////////////////////////////////////////////////////

DWORD
SNMP_FUNC_TYPE
SnmpSvcGetUptime(
    )

/*++

Routine Description:

    Retrieves sysUpTime for SNMP process.

Arguments:

    None.

Return Values:

    Returns sysUpTime value for use by subagents. 

--*/

{
    DWORD dwUpTime = INVALID_UPTIME;
        
    NTSTATUS NtStatus;
    SYSTEM_TIMEOFDAY_INFORMATION TimeOfDay;

    // query time in spiffy new precise manner        
    NtStatus = NtQuerySystemInformation(
                        SystemTimeOfDayInformation,
                        &TimeOfDay,
                        sizeof(SYSTEM_TIMEOFDAY_INFORMATION),
                        NULL
                        );
        
    // validate return code
    if (NT_SUCCESS(NtStatus)) {
        LARGE_INTEGER liUpTime;
        LARGE_INTEGER liUpTimeInCentaseconds;

        // calculate difference from reference
        liUpTime.QuadPart = TimeOfDay.CurrentTime.QuadPart - 
                                                    g_llUpTimeReference;
                                    
        // convert 100ns units (10^-7) into centasecond units (10^-2)
        liUpTimeInCentaseconds = RtlExtendedLargeIntegerDivide(
                                            liUpTime,
                                            100000,
                                            NULL
                                            );

        // convert large integer to dword value
        dwUpTime = (DWORD)(LONGLONG)liUpTimeInCentaseconds.QuadPart;
    
    } else if (g_dwUpTimeReference != 0) {

        // calculate difference from reference
        dwUpTime = (GetCurrentTime() - g_dwUpTimeReference) / 10;
    }

    return dwUpTime;
}

DWORD
SNMP_FUNC_TYPE
SnmpSvcGetUptimeFromTime(
    DWORD dwUpTime
    )

/*++

Routine Description:

    Retrieves sysUpTime value for a given tick count.

Arguments:

    dwUpTime - stack uptime (in centaseconds) to convert to sysUpTime

Return Values:

    Returns sysUpTime value for use by subagents.

--*/

{
    DWORD dwUpTimeReferenceInCentaseconds;

    // convert 100ns units (10^-7) into centasecond units (10^-2)
    dwUpTimeReferenceInCentaseconds = (DWORD)(g_llUpTimeReference / 100000);

    if (dwUpTime < dwUpTimeReferenceInCentaseconds) {
        return 0;
    }

    // calculate difference from reference
    return dwUpTime - dwUpTimeReferenceInCentaseconds;
}