Title: unionfs mini howto
Subject: This is an filesystem exercise, to expand how you see file systems.
  
Terms:  Squashfs - read-only filesystem, very compact.
        tmpfs    - read-write filesystem, ramdisk, temporary storage.
	unionfs  - filesystem overly system, overly writeable over readonly fs.

  REFERENCE: http://gentoo-wiki.com/HOWTO_Diskless:_Unionfs._Why_not%3F
  
# In gentoo install unionfs
  # 1st. Unpask
  echo 'sys-fs/unionfs ~x86' >> /etc/portage/package.keywords

  # 2nd. Version is kernel specific
  #      For Kernel 2.6.18 use unionfs-1.4
  #      For Kernel 2.6.19 use unionfs-1.5
  #
  emerge --deep --newuse =sys-fs/unionfs -ta

  # 3rd. Update module info
  depmod -a
  modules-update

  # 4th. Load moudle
  modprobe unionfs

  # 5th. Veirfy I have installed unionfs-1.5_pre200701042308
  eix -I unionfs

  [I] sys-fs/unionfs
     Available versions:  (~)1.0.14 (~)1.1.4-r2 (~)1.1.5 (~)1.2 (~)1.3 (~)1.4 (~)1.5_pre200701042308
     Installed versions:  1.5_pre200701042308(10:59:18 03/19/07)(-acl -debug kernel_linux -nfs)
     Homepage:            http://www.fsl.cs.sunysb.edu/project-unionfs.html
     Description:         Stackable unification file system, which can appear to merge the contents of several directories

  # 6th. Verify my gentoo kernel is 2.6.19-gentoo-r5
  uname -r
  
  2.6.19-gentoo-r5
  
  # 7th. Load unionfs
  modprobe unionfs

  # 8th. Check for loaded module
  lsmod  |grep union
    unionfs                79240  0
    exportfs                5280  1 unionfs


# Example using using 
  # 1st. Create 3 directories used in the example:
  mkdir /tmp/new_ro /tmp/new_rw /tmp/new

  # 2nd. Create a readonly mount of a squashfs to /tmp/new_ro
  mkdir -p /tmp/test/if/this/works
  mksquashfs /tmp/test /tmp/new_squash.sqsh -info -always-use-fragments
  mount -t squashfs -o loop /tmp/new_squash.sqsh  /tmp/new_ro

  # 3rd. Create a writeable mount of a tmpfs to /tmp/new_rw
  mount -t tmpfs -o size=50m none /tmp/new_rw

  # 4th. Create the Union of /tmp/new_rw over /tmp/new_ro as /tmp/new/
  mount -t unionfs -o dirs=/tmp/new_rw:/tmp/new_ro unionfs /tmp/new

  # 5th. Test write
  touch /tmp/new/foo
  ls -alF /tmp/new/

   total 1
   drwxrwxrwt  3 root root  60 Mar 21 17:53 ./
   drwxrwxrwt 20 root root 824 Mar 21 17:50 ../
   -rw-r--r--  1 root root   0 Mar 21 17:53 foo
   drwxr-xr-x  3 root root  21 Mar 21 17:35 if/

  # 6th. Cleanup
  unmount /tmp/new
  umount /tmp/new_*
  rm -rf /tmp/new*