snap-guest-tree

#!/usr/bin/ruby
# encoding: UTF-8

DEFAULT_IMAGES_DIR = "/var/lib/libvirt/images"

def usage
  <<DOC
Usage: #{File.basename(__FILE__)} [images_dir]

Prints tree of base-images and their copy-on-write snapshots. Useful for
determining dependencies between images.

Unless images_dir specified it searches images in '#{DEFAULT_IMAGES_DIR}'.
DOC
end

IMAGE_DIR = ARGV[0] || DEFAULT_IMAGES_DIR

unless File.directory?(IMAGE_DIR)
  puts usage
end

def qemu_images_hash
  images_hash = {}
  Dir.glob(File.join(IMAGE_DIR, "*")) do |file|
    img_info_str = `qemu-img info "#{file}"`
    img_info = {}
    img_info_str.each_line do |line|
      key, value = line.split(":", 2)
      img_info[key.strip] = value.chomp.strip
    end
    images_hash[img_info["image"]] = img_info
  end
  images_hash
end

def images_tree
  hierarchy_hash = qemu_images_hash
  hierarchy_hash.each do |(_, image_info)|
    if base = image_info["backing file"].to_s[/actual path: (.*)\)$/,1] || image_info["backing file"]
      hierarchy_hash[base]["children"] ||= []
      hierarchy_hash[base]["children"] << image_info
      image_info["base"] = hierarchy_hash[base]
    end
  end

  hierarchy_hash.delete_if {|k,v| v["base"]}
  images_hierarchy_to_tree(hierarchy_hash.values)
end

def images_hierarchy_to_tree(images_hierarchy)
  tree = {}
  images_hierarchy.each do |image_info|
    tree[image_info["image"]] =
      if children = image_info["children"]
        images_hierarchy_to_tree(children)
      else
        nil
      end
  end
  tree
end

# Converts tree hash such as:
#
#   {"1" => {
#      "1.1" => {
#        "1.2.1" => nil},
#      "1.2" => nil },
#    "2" => {
#      "2.1" => {
#        "2.1.2" => nil }}}
#
# into string in a form:
#   1
#   ├──1.1
#   │  └──1.2.1
#   └──1.2
#   2
#   └──2.1
#      └──2.1.2
def tree_pretty_print(hash, prefix = [])
  out = ""
  hash.each_with_index do |(key, children), index|
    last = index == (hash.size - 1)
    unless prefix.empty?
      bullet_width = 2
      if last
        prefix[-1] = "└"
      else
        prefix[-1] = "├"
      end
    else
      bullet_width = 0
    end
    out << prefix.join << ("─" * bullet_width) << key << "\n"
    unless prefix.empty?
      if last
        prefix[-1] = " "
      else
        prefix[-1] = "│"
      end
    end
    if children
      out << tree_pretty_print(children, prefix + [" "] * bullet_width + ["│"])
    end
  end
  out
end

puts tree_pretty_print(images_tree)