The structure of the COMM_FILE_SIZE packet element is as follows.

 typedef struct _COMM_FILE_SIZE {
   USHORT CommType;
   ULONG Length;
   ULONGLONG Data;
 } COMM_FILE_SIZE,
  *PCOMM_FILE_SIZE;

CommType: A 16-bit, unsigned integer that indicates the type of this COMM_PACKET element. MUST be set to 0x000B.

Length: A 32-bit, unsigned integer that indicates the length in bytes of the data following the Length field. MUST be 0x00000008.

Data: A 64-bit, unsigned integer that specifies the total size in bytes of the staged file.