bitbake: knotty, xmlrpc: add observer-only mode

I add an observer only mode for the knotty UI and
the XMLRPC server that will allow the UI to register
a callback with a server in order to receive events.

The observer-UI is able to send read-only commands to the
server, and also is able to register as an event handler.

Read-only commands are the commands that do not change
the state of the server and have been marked as such in
the command module.

The observer can switch to a full client if it calls addClient
at any time, and the server has no other client running.

(Bitbake rev: 4de9ee21f1fa4d04937cc7430fb1fc8b7a8f61e2)

Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/command.py

@@ -59,11 +59,14 @@ class Command:
         # FIXME Add lock for this
         self.currentAsyncCommand = None
 
-    def runCommand(self, commandline):
+    def runCommand(self, commandline, ro_only = False):
         command = commandline.pop(0)
         if hasattr(CommandsSync, command):
             # Can run synchronous commands straight away
             command_method = getattr(self.cmds_sync, command)
+            if ro_only:
+                if not hasattr(command_method, 'readonly') or False == getattr(command_method, 'readonly'):
+                    return None, "Not able to execute not readonly commands in readonly mode"
             try:
                 result = command_method(self, commandline)
             except CommandError as exc:
@@ -153,6 +156,7 @@ class CommandsSync:
             expand = params[1]
 
         return command.cooker.data.getVar(varname, expand)
+    getVariable.readonly = True
 
     def setVariable(self, command, params):
         """
@@ -200,6 +204,7 @@ class CommandsSync:
         Get the CPU count on the bitbake server
         """
         return bb.utils.cpu_count()
+    getCpuCount.readonly = True
 
     def matchFile(self, command, params):
         fMatch = params[0]