#ifndef _NTIOAPI_H
typedef struct _FILE_FS_FULL_SIZE_INFORMATION
{
LARGE_INTEGER TotalAllocationUnits;
LARGE_INTEGER CallerAvailableAllocationUnits;
LARGE_INTEGER ActualAvailableAllocationUnits;
ULONG SectorsPerAllocationUnit;
ULONG BytesPerSector;
} FILE_FS_FULL_SIZE_INFORMATION, *PFILE_FS_FULL_SIZE_INFORMATION;
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This structure is documented in Windows Driver Kit.