Script that will download the F22 cloud image and run fstrim and the compress it again.

fstrimcloudimage.sh

#!/bin/bash
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free  Software Foundation; either version 2 of the License, or
# (at your option)  any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
# MA 02110-1301 USA.
#
#
# purpose: This script will download a fedora image run fstrim and then cp
#          all images to /tmp/xzimg. It uses Docker to hopefully guarantee 
#          the behavior is consistent across different machines.
#  author: Dusty Mabe ([email protected])

set -eux 
mkdir -p /tmp/xzimg/

docker run -i --rm --privileged -v /tmp/xzimg:/tmp/xzimg fedora:22 bash << 'EOF'
set -eux
WORKDIR=/workdir
TMPMNT=/workdir/tmp/mnt

# Vars for the image
XZIMGURL='http://download.fedoraproject.org/pub/fedora/linux/releases/22/Cloud/x86_64/Images/Fedora-Cloud-Base-22-20150521.x86_64.raw.xz'
XZIMG=$(basename $XZIMGURL) # Just the file name
IMG=${XZIMG:0:-3}           # Pull .xz off of the end

# Create workdir and cd to it
mkdir -p $TMPMNT && cd $WORKDIR

# Get any additional rpms that we need
dnf install -y wget xz

# Get the xz image
wget $XZIMGURL
cp -a $XZIMG /tmp/xzimg/orig.raw.xz
unxz $XZIMG
cp -a $IMG /tmp/xzimg/orig.raw

# Find the starting byte and the total bytes in the 1st partition
# NOTE: normally would be able to use partx/kpartx directly to loopmount
#       the disk image and add the partitions, but inside of docker I found
#       that wasn't working quite right so I resorted to this manual approach.
PAIRS=$(partx --pairs $IMG)
eval `echo "$PAIRS" | head -n 1 | sed 's/ /\n/g'`
STARTBYTES=$((512*START))   # 512 bytes * the number of the start sector
TOTALBYTES=$((512*SECTORS)) # 512 bytes * the number of sectors in the partition

# Discover the next available loopback device
LOOPDEV=$(losetup -f)
LOOPDEV=/dev/loop3
LOMAJOR=''

# Make the loopback device if it doesn't exist already
if [ ! -e $LOOPDEV ]; then
    LOMAJOR=${LOOPDEV#/dev/loop} # Get just the number
    mknod -m660 $LOOPDEV b 7 $LOMAJOR
fi

# Loopmount the first partition of the device
losetup -v --offset $STARTBYTES --sizelimit $TOTALBYTES $LOOPDEV $IMG

# Mount it on $TMPMNT
mount $LOOPDEV $TMPMNT

# Fstrim to recover space
fstrim -v ${TMPMNT}

# one more time for good luck
fstrim -v ${TMPMNT}

# umount and tear down loop device
umount $TMPMNT
losetup -d $LOOPDEV
[ ! -z $LOMAJOR ] && rm -f $LOOPDEV #Only remove if we created it

# recompress the image
xz --stdout $IMG > $XZIMG

# finally, cp $IMG into /tmp/azureimg/ on the host
cp -a $IMG /tmp/xzimg/trimmed.raw 
cp -a $XZIMG /tmp/xzimg/trimmed.raw.xz

EOF