This directory (/mnt/tmpfs/dev on the root filesystem) will
be brutally overriden when the tmpfs is mounted. Its only
purpose is to provide an initial /dev/console to the kernel
when it starts process 1.
The directory should contain a working /dev/console device!

 init-stage1 will close all handles to this /dev/console,
then mount the tmpfs and copy the tmpfs image to the tmpfs
- the image contains a full version of /dev, which will then
be used.
 This trick is necessary to have a working read-write /dev
when you have a root-only filesystem and when you cannot or
do not want to rely on fancy Linux-specific tricks such as
devtmpfs.