Add the -C option to mount_mfs. This option will automatically copy the

Add the -C option to mount_mfs.  This option will automatically copy the
underlying filesystem into the MFS mount being created over it.  It does
this by loading the directory and file structure into memory, creating the
MFS mount, then storing the directory and file structure back into the MFS
mount.

This will be used when booting from read-only media to generate an 'easy'
read-write template.  For example:

    mount_mfs -s 16384 -C swap /var

Softlinks, devices, regular files, directories, and hardlinks are maintained.
Fifos and sockets are not copied.