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

christos