While working with some of my KVM vm's I needed the ability to take snapshots quickly as well as revert back to a desired point. The following shell functions are used in my bashrc to make it simple for me to accomplish these task. NOTE: These snapshots are only for the file system and require qcow2 disk images for the backing storage.

can_o_virt

#!/bin/bash

wake(){    # Start your VM
    sudo virsh start $1
}

slay(){    # Stop your VM
    sd_time=20
    sudo virsh shutdown $1
    if [[ $? ]]; then
        echo "Shutting Down VM, hold $sd_time seconds."
        sleep $sd_time
    fi
    echo "Checking to see if VM is down? (will kill VM violently if not!)"
    if [[ running == `sudo virsh list | grep $1 | awk '{print $3}'` ]]; then
        echo "Killing VM violently"
        sudo virsh destroy $1
    else
        echo "VM was shutdown successfuly!"
    fi
}

breed(){    # Create a qcow2 storage device
    if [[ -n "$1" ]] && [[ -n "$2" ]]; then
        sudo qemu-img create -f qcow2 /var/lib/libvirt/images/${1}.img ${2}G
    else
        echo "Disk Name or size (in GB) not supplied."
        echo "    breed NAME SIZE"
    fi
}

hatch(){    # Create a VM
    if [[ -n $1 ]]; then
        NAME=$1
    else
        echo "Must supply a VM name."
        echo "    hatch VM_NAME DISK_NAME RAM_SIZE NETWORK INSTALL_MEDIA"
        return 1
    fi
    if [[ -n $2 ]]; then
        DISK=/var/lib/libvirt/images/$2
    else
        echo "Must supply an image name. Try one of the following:" 
        ls /var/lib/libvirt/images/
        echo "    hatch VM_NAME DISK_NAME RAM_SIZE NETWORK INSTALL_MEDIA"
        return 1
    fi
    if [[ -n $3 ]]; then
        RAM=$3
    else
        echo "Must supply your RAM size in MB (1024 = 1GB)" 
        echo "    hatch VM_NAME DISK_NAME RAM_SIZE NETWORK INSTALL_MEDIA"
        return 1
    fi
    if [[ -n $4 ]]; then
        NETWORK=$4
    else
        echo "Must supply a VM Network. Try:"
        sudo virsh net-list | tail -n+3 | awk '{print $1}'
        echo "    hatch VM_NAME DISK_NAME RAM_SIZE NETWORK INSTALL_MEDIA"
        return 1
    fi
    if [[ -n $5 ]]; then
        INSTALL_IMAGE=$5
    else
        echo "Must supply the location of install media." 
        echo "    hatch VM_NAME DISK_NAME RAM_SIZE NETWORK INSTALL_MEDIA"
        return 1
    fi
    sudo virt-install --cdrom $INSTALL_IMAGE --name $NAME --ram $RAM --disk $DISK,bus="virtio" --network network=$NETWORK
}

hunt(){    # Get Snapshot informaion from the VM 
    if [[ -n "$1" ]]; then
        base_image=`sudo virsh domblklist $1 | grep vda | awk '{print $2}'`
    else 
        echo "Must supply Domain"
        return 1
    fi
    IP=$(ip neighbour | grep $(sudo virsh dumpxml $1 | grep "mac address" | awk -F\' '{ print $2 }') | awk '{ print $1 }')
    if [[ -z $IP ]]; then
        IP="Can Not Determin!"
    fi
    echo "Base Image: $base_image"
    echo IP: $IP
    sudo qemu-img snapshot -l $base_image
}

tame(){    # Create a Snapshot of a VM   # qemu-img snapshot -c SNAPSHOT BASE_IMAGE
# This assumes that you are using a VIRTIO device (need to find a better way of doing this.
    if [[ -n "$1" ]]; then
        base_image=`sudo virsh domblklist $1 | grep vda | awk '{print $2}'`
    else 
        echo "Must supply Domain"
        return 1
    fi
    
    if [[ -z $2 ]]; then
        echo "Must supply Snapshot Name"
    else
        # VM has to be down to save it's state.. 
        echo "Shutting down $1 to save it current disk state."
        sudo virsh shutdown $1
        if [[ running == `sudo virsh list | grep $1 | awk '{print $3}'` ]]; then
            echo "Killing VM violently"
            sudo virsh destroy $1
        fi

        echo "Base Image: $base_image"
        
        for snapshot in `sudo qemu-img snapshot -l $base_image | tail -n+3 | awk '{print $2}'`; do
            if [[ $snapshot == $2 ]]; then
                echo "Snapshot Already exsists! You can chose to overwrite or create a new snapshot with the same name."
                read -p "Would you like to overwrite[Y|y]? " -n 1 -r
                if [[ $REPLY =~ ^[Yy]$ ]]; then
                    echo " deleting snapshot ..."
                    sudo qemu-img snapshot -d $2 $base_image
                    echo "Deleted Snapshot ..."
                else
                    echo
                fi
                
            fi 
        done
        sudo qemu-img snapshot -c $2 $base_image
        echo "Snapshot Created!"
    fi
}

revive(){    # Apply a VM Snapshot
    if [[ -n "$1" ]]; then
        base_image=`sudo virsh domblklist $1 | grep vda | awk '{print $2}'`
    else
        echo "Must supply Domain"
        return 1
    fi
    if [[ -n "$2" ]]; then
        echo "reverting $base_image to $2 snapshot."

        slay $1

        sudo qemu-img snapshot -a $2 $base_image
        
        echo "    Revert Complete!" 
        sudo virsh start $1 
        return 0
    else 
        echo "Must Supply Snapshot!"
        echo "  Choose from the following:" 
        sudo qemu-img snapshot -l $base_image 
        return 1
    fi
    return 1
}