jail_set (pretty much) done

[James Gritton]

The name-based FreeBSD Jail extensions are now ready for use.  I've 
added support to the user-space programs (jail, jls, jexec), and added 
some fluff to the relevant man pages.

This still stands alone - I haven't yet integrated it with Vimage, which 
is the next step.  But it's there for anyone who wants to take a look at 
it on its own.  I've put diffs against Current in 
http://gritton.org/jail_set.diff, and I have a perforce branch in 
//depot/user/jamie/jail_set/.

In a nutshell, this adds three system calls: jail_get, jail_set, and 
jail_remove.  Jail_remove is a no-brainer.  The other two allow jails to 
be created and existing jails to be modified in a manner similar to the 
nmount system call.  The user-level jail and jls programs work with 
these system calls to set/get an arbitrary set of name-based jail 
parameters.  The system has a certain set of parameters, key among them 
the members of original jail structure, and modules are free to add 
their own parameters.  The linux OS info has been changed to use this 
setup as a demonstration (and because it's just better that way).

Hierarchical jails are supported (though turned off by default).

It's all in the updated jail(2) and jail(8) man pages.

- Jamie