bitbake: support $BITBAKE_UI environment

Patch adds support for a $BITBAKE_UI environment variable which allows
to configure the preferred user interface. Although an '-u' option
(which will override the environment variable) exists already, it was
required to specify this option on every invocation of bitbake.

Because user interface is instanciated very early in the program it is
not possible to use bitbake.conf for setting up a default.  An
environment variable (which acts in a similar category like $PAGER or
$EDITOR) is a simple way for configuring the default.

(Bitbake rev: e3c213015953d1a0afb5ef4be59e1264990e5cee)

Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/bin/bitbake

@@ -56,10 +56,11 @@ class BBConfiguration(object):
 
 
 def get_ui(config):
-    if config.ui:
-        interface = config.ui
-    else:
-        interface = 'knotty'
+    if not config.ui:
+        # modify 'ui' attribute because it is also read by cooker
+        config.ui = os.environ.get('BITBAKE_UI', 'knotty')
+
+    interface = config.ui
 
     try:
         # Dynamically load the UI based on the ui name. Although we

bitbake/doc/bitbake.1

@@ -103,7 +103,13 @@ Show debug logging for the specified logging domains
 .TP
 .B \-P, \-\-profile
 profile the command and print a report
+
+.SH ENVIRONMENT VARIABLES
+bitbake uses the following environment variables to control its
+operation:
 .TP
+.B BITBAKE_UI
+The bitbake user interface; overridden by the \fB-u\fP commandline option.
 
 .SH AUTHORS
 BitBake was written by