New jail framework - the userland side

[Jamie Gritton]

Poul-Henning Kamp wrote:
> In message <49FE5387.3020503 at FreeBSD.org>, Jamie Gritton writes:
> 
>> Hi all.  I recently added some new jail-related system calls to extend 
>> the current jail system with an nmount-inspired name=value interface.  
> 
> I think this is a great move in the right direction, my only concern is
> that we should try to share as much of the string-munging code between
> the nmount and jail implementations as possible.

Most if it is shared - jail actually calls vfs_getopt and related calls
from the family.  I might want to spin those functions off into their
own subsystem at some point, now that they're officially used outside
of VFS.

I did have to extend things somewhat for jail_get, as nmount is write-
only and only had to deal with one module at a time (the filesystem
type).  Those extensions are available for use elsewhere, as I suspect
filesystems and jails aren't the only place where we could use name-
based extensibility.

- Jamie