typedef enum _FSINFOCLASS
{
         FileFsVolumeInformation = 1,
         FileFsLabelInformation = 2,
         FileFsSizeInformation = 3,
         FileFsDeviceInformation = 4,
         FileFsAttributeInformation = 5,
         FileFsControlInformation = 6,
         FileFsFullSizeInformation = 7,
         FileFsObjectIdInformation = 8,
         FileFsDriverPathInformation = 9,
         FileFsVolumeFlagsInformation = 10,
         FileFsMaximumInformation = 11
} FSINFOCLASS;

Windows Vista Kernel Structures