I was going to call it shmem originally but thought better of it
after the flap over int/void main().

I added it at the request of a piece of Lucent that wants to
be able to have a large in memory database sharable by
unrelated processes.  Any process can see them but segattaching,
reading, and writing uses the file protections.  I may add that
restriction to removing also, haven't decided yet.

In the interest of being neighborly, I added it to the general
distribution.  I made it a separate device mostly because I
don't think its incredibly useful.  It has our normal
shared segment restriction that it must be at the
same virtual address in all processes that use it.
If you have locks in it, there's no mechanism for
backing out the locks held if a process dies.
It's very much a solution to a specific problem...

It's a little nicer than shmem in that
processes on other machines can get at the segment, albeit
with some difficulty, by importing the file system interface.