answers.txt: 6.828 Lab 5
Dan R. K. Ports <drkp@mit.edu>
2004/11/18:

Questions:

1. About 15 hours.


Challenge:

Implemented exec. I considered a number of possible approaches to
implementing this functionality in keeping with exokernel
principles. The most obvious implementation would be to implement it
entirely in kernel space -- but in addition to not being the Exokernel
Way, it requires the kernel to depend on the file server, which is
even more of a problem. 

Instead, the user process sets up a new address space as a child
environment, just as in spawn(). It then calls a new syscall,
sys_env_eat_child (which introduces a number of wonderfully tasteless
jokes to the kernel), which replaces the current process's address
space and trapframe with that of the child, then consumes the
child. This syscall isn't especially useful anywhere except in exec,
but it allows exec to be implemented mostly in user space.