mjhjmtu

I was looking at another question (https://stackoverflow.com/q/47845/537980), and saw an answer, about how much set up this other OS had to do, for every Process Create.

I got wondering. Would it be possible to do the setup (once, then fork), then do a partial exec to load the variable parts? That is only part of the process should be replaced.

A specific example of partial, would be. We want to load some execution environment, then exec to replace the loader, but not the environment. So this is taking control of what gets replaced (I know that exec does not replace everything (e.g. it keeps a COW of the file descriptor table)).

I realise that this may not have any practical use, as fork and exec are relatively cheep on many Unixes.

Partial answer of an untested idea

fork + exec can not do it, because exec replaces (almost) all of the process state.

The man page for clone suggests that, maybe clone + exec is flexible enough to allow this:

One could do the setup, then clone (with shared (non-writable) memory, for all resources that you want to be shared), then exec in the child. Execed program would be programmed to use resources in the parent (via shared memory).

Therefore exec did replace all of the process, however because of shared memory, because of clone, it was partial.

(Using clone, can blur the definition of a process. clone can be used to create threads, processes, and many other things in between.)