32-bit Windows-based applications must call the exclusive volume-locking IOCTL functions indirectly by opening VWIN32.VXD and using its DeviceIoControl interface.
In response, VWIN32.VXD issues the low-level disk I/O functions (Interrupt 13h, Interrupt 25h, and Interrupt 26h) as well as the MS-DOS Interrupt 21h file handle read, write, seek, and IOCTL functions in the context of the calling process.
32-bit Windows-based applications may safely call the Windows ReadFile, WriteFile, SetFilePointer, and DeviceIoControl functions within a level 3 lock. Other Windows or C run-time library functions should not be used while in the level 3 lock, because these functions may call other functions that are not safe inside a level 3 lock.