We need to pass all opened fds down to child processes

[OFFTKP]

Issue at hand:

Rootfs installed at $HOME (not recommended)
When child process tries to access rootfs, it tries to go through /home/user/rootfs

But if child processes has different uid/gid, it can't access /home/user
So it can't open rootfs, so nothing works
Example app: apt update

Solution:

We need to make sure:

• child processes use fd+path always, perhaps get rid of full_path() stuff
• instead of opening fds, inherit them
• disable all close on exec shenanigans, such as in fcntl