Union mount -b does not work as expected.
The file names accessible are seen neither to the shell globbing
mechanism nor to ls.
There seem to be other programs unable to find the files. (Just
try to configure and make gnuplot.)
$ mkdir dreck
$ /sbin/mount -t union -o -b gnuplot dreck
$ ls header.mac
$ ls *.mac
ls: *.mac: No such file or directory
The problem is known to be caused by readdir() not working for lkm'ed
union file systems.
Bruce wants to document in the FAQ that all union file system features should
be asssumed to be broken. I'll leave this bug open and assigned to him
as a reminder.
I won't be fixing this soon.
unionfs doesn't work, we know it.