>> > Either disallow two uses of the same image or provide a second changes
>> > file.
>
> Perhaps another option would be for the VM process to create a second 
> small
> "lock file" whenever the changes file is open for write, and remove it 
> when
> it's closed or the process exits. On startup, VM would check if the lock 
> file
> exists, if it does, will not start. Of course there is the problem of 
> crashes
> ..

There is no way to guarentee integerity of a shared changes/image file using 
locking. You would need some form of notification and reloading as well, 
either that or a shared memory mapped file. All too dangerous considering 
crashes and incompatible changes and more crashes, and lost work, and 
annoyance at machines behaviour for loosing work...

> Would something like that work and be implemented ..

Not really.

Aaron