synced_folders/smb: raise error if not windows

plugins/synced_folders/smb/errors.rb

@@ -17,6 +17,10 @@ module VagrantPlugins
       class PowershellError < SMBError
         error_key(:powershell_error)
       end
+
+      class WindowsHostRequired < SMBError
+        error_key(:windows_host_required)
+      end
     end
   end
 end

plugins/synced_folders/smb/synced_folder.rb

@@ -16,7 +16,7 @@ module VagrantPlugins
 
       def usable?(machine, raise_error=false)
         if !Vagrant::Util::Platform.windows?
-          # TODO: raise error if specified
+          raise Errors::WindowsHostRequired if raise_error
           return false
         end
 

templates/locales/synced_folder_smb.yml

@@ -37,3 +37,7 @@ en:
         Error:
 
         %{stderr}
+      windows_host_required: |-
+        SMB shared folders are only available when Vagrant is running
+        on Windows. The guest machine can be running non-Windows. Please use
+        another synced folder type.