#!/bin/sh
###########################################################################
##  Copyright (C) Wizardry and Steamworks 2017 - License: GNU GPLv3      ##
##  Please see: http://www.gnu.org/licenses/gpl.html for legal details,  ##
##  rights of fair usage, the disclaimer and warranty conditions.        ##
###########################################################################
# Live backup script for libvirt/qemu virtual machines using blockcommit. #
# The script is designed to query all the active libvirt domains, create  #
# a snap overlay, copy over the image or the block device to a file and   #
# finally merge the overlay with the image - all these operations are     #
# performed without needing to suspend or shut down the virtual machine.  #
#                                                                         #
# Requirements:                                                           #
#   * pxz (parallel xz)                                                   #
#                                                                         #
# Setup: Configure the script in the configuration section and then run   #
# the script - the script is designed to be run from cron.                #
###########################################################################

###########################################################################
#                             CONFIGURATION                               #
###########################################################################

# This absolute path to a directory where the machines will be stored.
BACKUP_DIRECTORY=/mnt/archie/Backups/VMS

# A temporary directory to hold the temporary snapshots.
SNAP_DIRECTORY=/var/lib/libvirt/snapshots

# A space-separated list of domains to exclude from backup.
EXCLUDE_DOMAINS="corrade.internal"

###########################################################################
#                                INTERNALS                                #
###########################################################################

# Get active domains.
DOMAINS=`virsh -c qemu:///system list | grep -o '[0-9]* [a-z]*.*running' | awk '{print $2}'`
# Generate a timestamp.
TIMESTAMP=`date +%Y%m%d`

# Acquire lock.
if mkdir /var/lock/virsh-backup; then
    for DOMAIN in $DOMAINS; do
        # Check if this domain has been excluded.
        for EXCLUDE in $EXCLUDE_DOMAINS; do
            if [ "$DOMAIN" = "$EXCLUDE" ]; then
                DOMAIN=""
            fi
        done
        if [ -z "$DOMAIN" ]; then
            continue;
        fi
        # Get block devices.
        VIRT_BLOCK_DEVICE=`virsh domblklist "$DOMAIN" | grep '/' | head -1 | awk '{print $1}'`
        HOST_BLOCK_DEVICE=`virsh domblklist "$DOMAIN" | grep '/' | head -1 | awk '{print $2}'`
        if [ -z "$VIRT_BLOCK_DEVICE" ]; then
            echo "Block device not found for domain "$DOMAIN
            continue;
        fi
        if [ ! -d "$SNAP_DIRECTORY" ]; then
            mkdir -p "$SNAP_DIRECTORY"
        fi
        # Create snapshot
        virsh snapshot-create-as \
           --domain "$DOMAIN" "$DOMAIN-snap-$TIMESTAMP" \
           --diskspec "$VIRT_BLOCK_DEVICE",file="$SNAP_DIRECTORY/$DOMAIN-snap-$TIMESTAMP" \
           --disk-only \
           --atomic \
           --no-metadata \
           --quiesce >/dev/null 2>&1
       if [ "$?" -ne "0" ]; then
           echo "Failed snapshoting domain "$DOMAIN
           continue;
       fi
       if [ ! -f "$SNAP_DIRECTORY/$DOMAIN-snap-$TIMESTAMP" ]; then
           echo "Snapshot file for domain "$DOMAIN" does not exit"
           continue;
       fi
       if [ ! -d "$BACKUP_DIRECTORY/$DOMAIN" ]; then
           mkdir -p "$BACKUP_DIRECTORY/$DOMAIN"
       fi
       dd if="$HOST_BLOCK_DEVICE" \
           conv=noerror status=none \
           bs=1M | pxz -0 > "$BACKUP_DIRECTORY/$DOMAIN/$TIMESTAMP.img.xz"
       virsh blockcommit "$DOMAIN" "$VIRT_BLOCK_DEVICE" \
           --active \
           --pivot >/dev/null 2>&1
       if [ "$?" -ne "0" ]; then
           echo "Could not commit back snapshot for domain "$DOMAIN
           continue;
       fi
       rm "$SNAP_DIRECTORY/$DOMAIN-snap-$TIMESTAMP"
    done
    
    # Release lock.
    rm -rf /var/lock/virsh-backup
fi