Int 6F Fn 07  - 10net - Lock Handle                                        [N]

   AH = 07h
   BX = file handle
   CX:DX = starting offset in file
   SI = record length

Return: CF clear if successful
   CF set on error
       AX = error code (see also AH=00h)
       0002h file not found

See Also: AH=08h"10NET",AH=0Fh,INT 21/AH=5Ch