[Toybox] Anybody familiar with fsopen() and friends?

[Rob Landley]

The documentation is still working its way through...

https://manpages.debian.org/unstable/manpages-dev/fsopen.2.en.html

I complained that linux didn't have mountat() and somebody said 
fsopen+fsconfig+fsmount+move_mount was the way to do that and pointed me 
at the above (pending) man page. I'm wondering if unshare or switch_root 
or something should use that. (2026-7=2019. I dunno how long glibc/musl 
took to trail the kernel here, and then distro releases, but it's been 
in the kernel's git repo for 7 years anyway...)

Rob