In article <20070216000441.GN21463@che.ojctech.com>,
   David Young  <dyoung@pobox.com> wrote:
   >On Thu, Feb 15, 2007 at 11:55:51PM +0000, Geoff Wing wrote:
   >> David Young <dyoung@pobox.com> typed:
   >> : Is there anywhere TMPFS cannot replace MFS, and work at least as well?
   >> : If not, is it ok if we begin to phase MFS out?
   >> 
   >> It doesn't have whitespace objects (so you can't do upper layer union mounts
   >> with it).
   >
   >Do you use union mounts in this way on /dev/, today, or is this purely
   >hypothetical?  I ask because I have never been able to rely on union
   >mounts for anything, although it is my understanding that reliably may
   >have improved with recent changes by Chuck Silvers.
   
   fdesc is a union mount in /dev:
   
   fdesc          /dev                    fdesc   rw,union         0 0


note that "union mount" and "unionfs" are separate things.  one is
"mount -t union", one is "mount -o union".

a union mount (-o) has no requirement for whiteouts...  this
functionality has been stable since ~forever.  unionfs is the
problem child.


.mrg.