script to create a faulty mount

create_faulty_mount.sh

#!/usr/bin/bash
#
# Script to create a faulty directory.

# Canonicalize the input directory.
faulty_device=`readlink -f $1`
echo Using file as the base of the loop device: $faulty_device

# Create a file large enough to hold the fs. The minimum size is 512B.
# Adjust `bs` based on the output of `state -f "%k" .` (tells you the block size of `.`)
# Adjust `count` based on the desired size of the filesystem.
dd if=/dev/zero of=$faulty_device bs=1024 count=1024

# Create a loop device out of the file.
losetup -f $faulty_device

loop_device=''

# Allow parsing of '\n'-terminated lines
IFS=$'\n'

# Get the name of the loop device we just created.
for dev in `losetup -a | grep $faulty_device`; do
  echo "$dev";
  loop_candidate=`echo $dev | sed -r 's/(\/dev\/loop[0-9]+).*/\1/'`;
  if [ "$dev" != "$loop_device" ]; then
    loop_device=$loop_candidate
    break;
  fi
done
if [ "$loop_device" == "" ]; then
  echo Could not find a loop device for $faulty_device
  rm $faulty_device
  exit 0
fi
echo Using first found loop device for $faulty_device: $loop_device

# Get the name of the first available md device.
highest_md=""
for line in `cat /proc/mdstat`; do
  echo $line
  md_candidate=`echo $line | sed -r 's/md([0-9]+)\s*:.*/\1/'`;
  if [ "$line" != "$md_candidate" ]; then
    highest_md=$md_candidate
    break;
  fi
done;
md_int="0"
if [ "$highest_md" == "" ]; then
  echo No md instances found
else
  echo Last md instance found: md$highest_md
  # Convert the md to an int and add 1.
  md_int=$(expr $highest_md + 1)
fi
md=/dev/md$md_int

unset IFS

echo Creating device $md
mdadm --create $md --level=faulty --raid-devices=1 $loop_device
mkfs.ext4 $md

echo To mount the device, run: mount $md <your_mountpoint>
echo After mounting, <your_mountpoint> can be used normally as a directory.
echo To fail the directory, run: mdadm --grow $md -l faulty -p write-all