bitbake: process/cooker: Allow UI process to know if the cooker was started successfully

Currently if the server fails to start, the user sees no error message and
the server will be repeatedly attempted to be started until some longer
timeouts expire. There are error messages in the cookerdeamon log but
nobody thinks to look there.

Add in a pipe which can be used to tell the starting process whether the cooker
did actually start or not. If it fails to start, no further attempts can be
made and if present, the log file can be shown to the user.

[YOCTO #11834]

(Bitbake rev: 57000d44beb1aeba37dfc70782b0d6418943acc5)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/cooker.py

@@ -165,7 +165,7 @@ class BBCooker:
     Manages one bitbake build run
     """
 
-    def __init__(self, configuration, featureSet=None):
+    def __init__(self, configuration, featureSet=None, readypipe=None):
         self.recipecaches = None
         self.skiplist = {}
         self.featureset = CookerFeatures()
@@ -237,6 +237,10 @@ class BBCooker:
         # Let SIGHUP exit as SIGTERM
         signal.signal(signal.SIGHUP, self.sigterm_exception)
 
+        if readypipe:
+            os.write(readypipe, b"ready")
+            os.close(readypipe)
+
     def config_notifications(self, event):
         if event.maskname == "IN_Q_OVERFLOW":
             bb.warn("inotify event queue overflowed, invalidating caches.")