> What is wrong with just using union mounts[1]?

I use union mounts, and they work pretty well, but there are still two
inconveniences:

First, when making i386 bootfiles, using the /dev/vnd* devices causes
the system to freeze.  (Specifically, if after you unmount the
/dev/vnd device, you "ls" the directory that contains the file, the
system hangs.)

Second, you can accumulate whiteout objects where you don't want them.
It would be nice if, for instance, there were a "find . -type W"
option to find to be able to do things like "find . -type W -print |
xargs rm -W".

Other than that, though, union mounts are great (particularly since
you don't need to be root to perform one).

David