EuroBSDcon slides: pivot_root for BSD including NetBSD code

[Adrian Steinmann <ast%netbsd.org@localhost>]

I have just delivered a presentation on pivot_root at EuroBSDcon
and have put up the most important slides, a patch including new files
against HEAD 20121017, and a custom ramdisk build I used to demonstrate
pivot_root here:

http://marabu.ch/pivot_root_eurobsdcon_2012/index.html

I looking for feedback especially if we should integrate this
into a mount -t pivot / mount_pivot program piggy-backing the
mount syscall instead of giving it its own syscall which would
entail a libc bump. The patch above still uses a new syscall (hence
touches quite a few files on only one line) and the userland
program "pivot_root" calls the syscall by number so don't forget
to modload the kmod :-) First feedback seems to indicate we prefer
integration into mount.

A yet unimplemented feature which would make this much more useful
would be to pivot the rootfs, but then move all the other mount
points under root to follow the new root. For example, /usr/pkg
would not end up in /put_old/usr/pkg but "stay" /usr/pkg (but
naturally now having the mountpoint on new_root). This would
obviate the need to restart services that have open filedescriptors
on file systems other than new_root and the original root. I do not
think this would be too hard to do and will investigate this feature.
Thank you Veego for this feedback!

Ast