Test for overlayfs bug.

#!/bin/bash
(
set -e
mkdir -p /mnt/test /tmp/usr
mount none /mnt/test -t overlayfs -o lowerdir=/usr,upperdir=/tmp/usr
/mnt/test/bin/tail -f /dev/null&
ls -lart /proc/$!/exe
kill $!
umount /mnt/test
rmdir /mnt/test /tmp/usr
)

# If a red broken link to /bin/tail is printed then the bug exists. If the link points to /mnt/test/bin/tail then there is no bug in the currently running kernel.