Revert tmpfs mount removal

To fix #406, I reverted the tmpfs mount we add at boot time. As we can
see in #455, it was a bad idea.

In addition to bringing back that mount, I've also added a
`tmpfs_mount_size` config that allows to change the size of the mount
from its default `2G`. It's also possible to disable the mount
altogether.

fixes #455

lib/vagrant-lxc/action.rb

@@ -12,7 +12,6 @@ require 'vagrant-lxc/action/handle_box_metadata'
 require 'vagrant-lxc/action/prepare_nfs_settings'
 require 'vagrant-lxc/action/prepare_nfs_valid_ids'
 require 'vagrant-lxc/action/private_networks'
-require 'vagrant-lxc/action/remove_temporary_files'
 require 'vagrant-lxc/action/setup_package_files'
 require 'vagrant-lxc/action/warn_networks'
 
@@ -125,9 +124,6 @@ module Vagrant
             end
 
             b2.use ClearForwardedPorts
-            if env[:machine].state.id == :running
-              b2.use RemoveTemporaryFiles
-            end
             b2.use GcPrivateNetworkBridges
             b2.use Builtin::Call, Builtin::GracefulHalt, :stopped, :running do |env2, b3|
               if !env2[:result]

lib/vagrant-lxc/action/boot.rb

@@ -26,6 +26,11 @@ module Vagrant
             config.customize 'mount.entry', '/sys/fs/selinux sys/fs/selinux none bind,ro 0 0'
           end
 
+          if config.tmpfs_mount_size && !config.tmpfs_mount_size.empty?
+            # Make /tmp a tmpfs to prevent init scripts from nuking synced folders mounted in here
+            config.customize 'mount.entry', "tmpfs tmp tmpfs nodev,nosuid,size=#{config.tmpfs_mount_size} 0 0"
+          end
+
           env[:ui].info I18n.t("vagrant_lxc.messages.starting")
           env[:machine].provider.driver.start(config.customizations)
 

lib/vagrant-lxc/action/remove_temporary_files.rb

@@ -1,23 +0,0 @@
-module Vagrant
-  module LXC
-    module Action
-      class RemoveTemporaryFiles
-        def initialize(app, env)
-          @app    = app
-          @logger = Log4r::Logger.new("vagrant::lxc::action::remove_tmp_files")
-        end
-
-        def call(env)
-          @logger.debug 'Removing temporary files'
-          driver = env[:machine].provider.driver
-          # To prevent host-side data loss, it's important that all mounts under /tmp are unmounted
-          # before we proceed with the `rm -rf` operation. See #68 and #360.
-          driver.attach("findmnt -R /tmp -o TARGET --list --noheadings | xargs -L 1 --no-run-if-empty umount")
-          driver.attach("rm -rf /tmp/*")
-
-          @app.call env
-        end
-      end
-    end
-  end
-end

lib/vagrant-lxc/config.rb

@@ -18,6 +18,10 @@ module Vagrant
       # machine name, set this to :machine
       attr_accessor :container_name
 
+      # Size (as a string like '400M') of the tmpfs to mount at /tmp on boot.
+      # Set to false or nil to disable the tmpfs mount altogether. Defaults to '2G'.
+      attr_accessor :tmpfs_mount_size
+
       attr_accessor :fetch_ip_tries
 
       def initialize
@@ -25,6 +29,7 @@ module Vagrant
         @backingstore = UNSET_VALUE
         @backingstore_options = []
         @container_name = UNSET_VALUE
+        @tmpfs_mount_size = UNSET_VALUE
         @fetch_ip_tries = UNSET_VALUE
       end
 
@@ -52,6 +57,7 @@ module Vagrant
         @container_name = nil if @container_name == UNSET_VALUE
         @backingstore = "best" if @backingstore == UNSET_VALUE
         @existing_container_name = nil if @existing_container_name == UNSET_VALUE
+        @tmpfs_mount_size = '2G' if @tmpfs_mount_size == UNSET_VALUE
         @fetch_ip_tries = 10 if @fetch_ip_tries == UNSET_VALUE
       end
     end