why mount --bind for permissions?

[Eric Sandeen <sandeen@xxxxxxx>]

I was experimenting with saving permissions in /dev via devfsd, and I
was wondering - why is 

mount --bind /dev-state /dev

necessary?  It seems that 

REGISTER     .*      COPY    /dev-state/$devname $devpath
CHANGE       .*      COPY    $devpath /dev-state/$devname
CREATE       .*      COPY    $devpath /dev-state/$devname

in devfsd.conf would copy everything back and forth whenever appropriate
- I'm not that familiar with "mount --bind" - but what does it add to
the equation?  Sorry if I'm being dense.  :)

Thanks,

-Eric

-- 
Eric Sandeen      XFS for Linux     http://oss.sgi.com/projects/xfs
sandeen@xxxxxxx   SGI, Inc.