#!/bin/bash
# this script demonstrates how to access devices or files which are located
# somewhere that has been mounted later

# Just run './mount-tricks' to run the demo
# run './mount-tricks undo' to clean up mounts and loop device

if [[ $1 = undo ]] ; then
	umount /mnt/test2
	#umount /mnt/test1
	umount /dev/loop0
	losetup -d /dev/loop0
	rm -rf /mnt/test1 /mnt/test2 /mnt/looptest
	exit
fi

# create 3 mount points
echo "Creating /mnt/looptest /mnt/test1 /mnt/test2"
mkdir -p /mnt/looptest /mnt/test1 /mnt/test2

# make a small partition image to test with
echo "Creating a small partition image"
dd if=/dev/zero of=/mnt/test1/test.img bs=1k count=5120
echo "Formatting partition image"
echo y | mke2fs /mnt/test1/test.img

echo
echo
# associate the test image with loop0
echo "Setting up /mnt/test1/test.img on loop device /dev/loop0"
losetup /dev/loop0 /mnt/test1/test.img
# mount the looped image device on 
echo "Mounting the loop device on /mnt/test1"
mount -t ext2 /dev/loop0 /mnt/looptest
# copy some stuff in there
echo "Now creating a couple of test files /mnt/test1/testfile1 & /mnt/test1/testfile2"
echo testme > /mnt/looptest/testfile1
echo testmetoo > /mnt/looptest/testfile2
echo
# show the output
echo "ls /mnt/test1: (directory where the test.img is located"
ls /mnt/test1
echo "ls /mnt/looptest: (directory where the test.img is loop mounted"
ls /mnt/looptest
echo "contents of /mnt/looptest/testfile1:"
cat /mnt/looptest/testfile1
echo "contents of /mnt/looptest/testfile2:"
cat /mnt/looptest/testfile2
echo "Press ENTER to continue"
read


echo =====
# now mount with bind
echo "mounting /mnt/test1 using bind on /mnt/test2"
mount --bind /mnt/test1 /mnt/test2
echo "ls /mnt/test1:"
ls /mnt/test1
echo "ls /mnt/test2:"
ls /mnt/test2
echo "Here /mnt/test2 mirrors the contents of /mnt/test1"
echo "Press ENTER to continue"
read

#
echo "now mounting /mnt/test1 on tmpfs"
mount -t tmpfs tmpfs /mnt/test1
echo "ls /mnt/test1:"
ls /mnt/test1
echo "ls /mnt/test2:"
ls /mnt/test2
echo "ls /mnt/looptest:"
ls /mnt/looptest
echo "Now, when /mnt/test1 is mounted on tmpfs"
echo "the contents disappear there, but not in /mnt/test2"
echo "and the contents in the loop device are also still there"
echo "Press ENTER to continue"
read

echo =====
echo "Now creating a file under /mnt/test1 which is mounted on tmpfs"
echo testme3 > /mnt/test1/testfile3
echo "ls /mnt/test1:"
ls /mnt/test1
echo "ls /mnt/test2:"
ls /mnt/test2
echo "ls /mnt/looptest:"
ls /mnt/looptest

echo =====
echo "Now unmounting tmpfs"
umount /mnt/test1
echo "ls /mnt/test1:"
ls /mnt/test1
echo "ls /mnt/test2:"
ls /mnt/test2
echo "ls /mnt/looptest:"
ls /mnt/looptest
echo "After unmounting /mnt/test1 from tmpfs"
echo "The original contents are visble again,"
echo "and what was written there while mounted tmpfs is gone"
#mount -t tmpfs tmpfs /mnt/loop