> Is the best approach to remove /sys as a symlink to /usr/src/sys, and make
> it a directory (or a symlink to /home/jelibean/sys as their isn't *that*
> much space on my root partition), and then
> 
> mount -t union -b /usr/src/sys /sys
> 
> to mount the real sys *underneath* /usr/src/sys ??
> 
> My understand is that if I then (for example) apply a set of kernel diffs
> distributed by someone who makes a custom kernel, the new versions of the
> files will be created in /sys, and next time I run sup it will be able to
> apply it's changes 'underneath' (obviously I will still need to re-patch).
> 
> Also, if I make some modifications (like adding debuggin printf's to
> routines I am working on) then they will also not affect my clean sup'ed
> source tree.
> 
> Do any of you -current die-hards have particular comments on this approach
> or better ways to do it?

This is pretty much the procedure I use.  The only caveat is that, once 
you've modified something, the original is no longer visible, _even_ if 
you subsequently delete the modified file!  (A white-out gets created to 
keep the original hiddden.)  What I do to get around this is to unmount 
the union fs, delete the file, and then re-mount the union fs.