guests/arch: compute netmask

Arch expects /24 for netmask, but users usually specify as a netmask
block like 255.255.255.0. This automatically converts it.

plugins/guests/arch/cap/configure_networks.rb

@@ -1,3 +1,5 @@
+require "ipaddr"
+require "socket"
 require "tempfile"
 
 require_relative "../../../../lib/vagrant/util/template_renderer"
@@ -17,6 +19,13 @@ module VagrantPlugins
           networks.each.with_index do |network, i|
             network[:device] = interfaces[network[:interface]]
 
+            # Arch expects netmasks to be in the "24" or "64", but users may
+            # specify IPV4 netmasks like "255.255.255.0". This magic converts
+            # the netmask to the proper value.
+            if network[:netmask] && network[:netmask].to_s.include?(".")
+              network[:netmask] = (32-Math.log2((IPAddr.new(network[:netmask], Socket::AF_INET).to_i^0xffffffff)+1)).to_i
+            end
+
             entry = TemplateRenderer.render("guests/arch/network_#{network[:type]}",
               options: network,
             )

templates/guests/arch/network_static.erb

@@ -2,7 +2,7 @@ Connection=ethernet
 Description='A basic static ethernet connection'
 Interface=<%= options[:device] %>
 IP=static
-Address=('<%= options[:ip]%>/24')
-<% if options[:gateway] %>
+Address=('<%= options[:ip]%>/<%= options[:netmask] %>')
+<% if options[:gateway] -%>
 Gateway='<%= options[:gateway] %>'
-<% end %>
+<% end -%>

templates/guests/arch/network_static6.erb

@@ -2,7 +2,7 @@ Connection=ethernet
 Description='A basic IPv6 ethernet connection'
 Interface=<%= options[:device] %>
 IP6=static
-Address=('<%= options[:ip]%>/<%= options[:netmask] %>')
-<% if options[:gateway] %>
-Gateway='<%= options[:gateway] %>'
-<% end %>
+Address6=('<%= options[:ip]%>/<%= options[:netmask] %>')
+<% if options[:gateway] -%>
+Gateway6='<%= options[:gateway] %>'
+<% end -%>