Article ID: 246689
Article Last Modified on 2/22/2007
APPLIES TO
- Microsoft Windows 2000 Server
- Microsoft Windows 2000 Advanced Server
- Microsoft Windows 2000 Professional Edition
- Microsoft Windows 98 Standard Edition
This article was previously published under Q246689
SUMMARY
The version of the GQoS on Windows 2000 is version 4 (GQoSv4). The version of the GQoS on Windows 98 and Microsoft Windows 98 Second Edition is version 1 (GQoSv1). The WSAEnumProtocols function can be used to determine the version of the GQoS.
Using WSAIoctl with the SIO_GET_QOS control code can be different because GQoSv4 and GQoSv1 differ in how the API can and must be called. The differences are as follows:
- GQoSv4 allows you to query the system to determine how large an output buffer you need in order to retrieve the QOS structure(s) whereas with GQoSv1 you must pass in a large enough buffer.
- GQoSv4 requires the output buffer to be contiguous whereas GQoSv1 does not.
- GQoSv4 requires that the supplied output buffer be large enough to contain all the Quality of Service (QOS) data (specifically the variable length provider-specific data in addition to the fixed size flowspec data); otherwise, none of the information will be returned, whereas GQoSv1 returns the portion of the provider-specific data (complete provider-specific QOS objects only) that can fit in the supplied provider-specific buffer.
- GQoSv1 requires that the output buffer be initialized so that the provider-specific pointer in the QOS structure points to valid memory, whereas GQoSv4 treats the buffer strictly as an output-only parameter (as it should).
As background, the WSAIoctl function is called with the SIO_GET_QOS control code to retrieve one or more QOS structures from the system. Typically this is done in response to the receipt of an FD_QOS as a result of using either the WSAAsyncSelect or WSAEventSelect function. A high performance server application that utilizes Quality of Service most likely would not call either WSAAsyncSelect or WSAEventSelect but would instead call WSAIoctl(SIO_GET_QOS) in an overlapped manner, perhaps even by using I/O Completion Ports (IOCP).
MORE INFORMATION
The following code snippet demonstrates a technique that can be used to call WSAIoctl with the SIO_GET_QOS control code on either GQoSv1 or GQoSv4, and takes into account the differences outlined earlier:
DWORD dwBytesReturned=0;
DWORD status;
DWORD dwBufferLen;
CHAR *pBuf = NULL;
QOS *pTempQos = NULL;
QOS *pQos = NULL;
if (GQOSv1)
// For GQOSv1 we must pick a buffer size
dwBufferLen = 2048;
else
{
// For GQOSv4 we can query the system to determine
// how large a buffer we need to pass in.
dwBufferLen = 0;
status = WSAIoctl(sd, SIO_GET_QOS, NULL, 0,
&dwBufferLen, sizeof(dwBufferLen),
&dwBytesReturned, NULL, NULL);
if (SOCKET_ERROR == status)
{
DWORD dwErr = WSAGetLastError();
if (WSAEWOULDBLOCK == dwErr)
{
// nothing to do
return(FALSE);
}
else if (WSAENOBUFS != dwErr)
{
// some sort of error not related to passing a
// large enough buffer
printf("WSAIoctl(SIO_GET_QOS)-query: %d\n",dwErr);
return(FALSE);
}
}
}
// For Windows 98 dwBufferLen has been set above, for
// Windows 2000 we queried the OS for the proper buffer size
printf("dwBufferlen for pQos = %d\n", dwBufferLen);
if (!(pBuf = (CHAR *)malloc(dwBufferLen)))
{
printf("malloc: %d\n", GetLastError());
return(FALSE);
}
// GQOSv1 workaround - not needed for GQOSv4, but doesn't
// hurt. GQOSv1 needs the provider specific buffer to point
// to valid memory, whereas GQOSv4 simply needs a contiguous
// block of memory. Therefore we allocate a contiguous block of
// memory cast it to a QOS structure and then set the provider
// specific buffer pointer to just beyond the QOS structure
// proper. GQOSv1 needs this whereas GQOSv4 ignores this.
// GQOSv1 should not care, because this is strictly an output
// buffer, GQOSv4 corrects this problem.
pTempQos = (QOS *)pBuf;
pTempQos->ProviderSpecific.buf = pBuf + sizeof(QOS);
pTempQos->ProviderSpecific.len = dwBufferLen - sizeof(QOS);
// end GQOSv1 workaround
status = WSAIoctl(sd, SIO_GET_QOS, NULL, 0,
pBuf, dwBufferLen, &dwBytesReturned,
NULL, NULL);
if (SOCKET_ERROR == status)
{
DWORD dwErr = WSAGetLastError();
free((char *)pBuf);
if (WSAEWOULDBLOCK != dwErr)
{
printf("WSAIoctl(SIO_GET_QOS) %d\n", dwErr);
}
return(FALSE);
}
pQos = (QOS *)pBuf;
Keywords: kbdswnet2003swept kbapi kbgqos kbhowto kbnetwork KB246689
