typedef enum _ARBITER_REQUEST_SOURCE
{
         ArbiterRequestUndefined = -1,
         ArbiterRequestLegacyReported = 0,
         ArbiterRequestHalReported = 1,
         ArbiterRequestLegacyAssigned = 2,
         ArbiterRequestPnpDetected = 3,
         ArbiterRequestPnpEnumerated = 4
} ARBITER_REQUEST_SOURCE;

Windows Vista Kernel Structures