Hey everyone,

I am running into a problem PInvoking a particular method I expose in a
DLL, that basically configures and starts an ETW session
(http://msdn.microsoft.com/library/default.asp?url=/library/en-us/perfmon/base/co
nsuming_events.asp).

The basic method looks like this:

__declspec(dllexport) HResult SartETWTrace(TraceHandle* traceHandle,
LPCTSTR logSessionName, LPCTSTR logFilePath)
{
EVENT_TRACE_PROPERTIES* pProperties = NULL;
ULONG BufferSize = 0;
ULONG rc = 0;
TRACEHANDLE SessionHandle = 0;

BufferSize = sizeof(EVENT_TRACE_PROPERTIES) + sizeof(logFilePath) +
sizeof(logSessionName);
pProperties = (EVENT_TRACE_PROPERTIES*) malloc(BufferSize);
if (NULL == pProperties)
{
 wprintf(L"Unable to allocate %d bytes for properties structure.\n",
BufferSize);
 return S_FALSE;
}

ZeroMemory(pProperties, BufferSize);
pProperties->Wnode.BufferSize = BufferSize;
CopyMemory((PVOID)&(pProperties->Wnode.Guid), &MyTraceSession,
sizeof(GUID));
pProperties->LoggerNameOffset = sizeof(EVENT_TRACE_PROPERTIES);
pProperties->LogFileNameOffset = sizeof(EVENT_TRACE_PROPERTIES) +
sizeof(logSessionName);
wcscpy((LPWSTR)((char*)pProperties + pProperties->LogFileNameOffset),
logFilePath);

rc = StartTrace((PTRACEHANDLE)&SessionHandle, logSessionName,
pProperties);
if (ERROR_SUCCESS != rc)
{
 wprintf(L"StartTrace() failed, %d\n", rc);
 return S_FALSE;
}

free(pProperties);
pProperties = NULL;
*traceHandle = SessionHandle;

return S_OK;
}

[DllImport("ETWWrapper.dll")]
public static extern void SartETWTrace([Out] out ulong sessionHandle,
[In] string sessionName, [In] string logFilePath);

string sessionName = "sessionName";
string logFilePath = "C:\someLog.etl";
ulong sessionHandle;

SartETWTrace(out sessionHandle, sessionName, sessionHandle);

The method fails because StartTrace returns ERROR_BAD_LENGTH, which
means the size of the created properties structure is properly off.
This works fine when I hard code and define the paths in the C++ DLL
itself, but the properties node seem to be improperly created and
initialized when I pass in the strings from the managed land.

Any help/suggestions on this problem would be greatly appreciated!

Thanks

Ines