implemented:
- Pages can be shared between maps.
- A change made to a map is written to the file, at munmap().
not yet implemented:
- VM operation during page IO execution.
Because page IO is executed with VM's lock.
- Page IO, which does not change a file size with any case.
When munmap() races with truncate(), the file size may be changed
illegally.
It was able to change a read-only memory using a system call that
forwarded to host.
To fix this, when read-only mmap(), it places read-only vm_area in the
mcexec's space.
allow the substitute of maps from mcexec thread to the syscall channel
the temporary correction of the problem that gethostbyname() after
accept() interruption finishes an error.
