Update cbuildbot.py to use emptytree option instead of deleting board.

bin/cbuildbot.py

 #!/usr/bin/python
 
 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """CBuildbot is wrapper around the build process used by the pre-flight queue"""
 
 import errno
 import heapq
@@ skipping 323 matching lines @@
   return binhost.rstrip('\n')
 
 
 def _SetupBoard(buildroot, board='x86-generic'):
   """Wrapper around setup_board."""
   cwd = os.path.join(buildroot, 'src', 'scripts')
   RunCommand(['./setup_board', '--fast', '--default', '--board=%s' % board],
              cwd=cwd, enter_chroot=True)
 
 
-def _Build(buildroot):
+def _Build(buildroot, emptytree):
   """Wrapper around build_packages."""
   cwd = os.path.join(buildroot, 'src', 'scripts')
-  RunCommand(['./build_packages'], cwd=cwd, enter_chroot=True)
+  cmd = ['./build_packages']
+  if emptytree:
+    cmd.insert(0, 'EXTRA_BOARD_FLAGS=--emptytree')
+
+  RunCommand(cmd, cwd=cwd, enter_chroot=True)
 
 
 def _BuildChrome(buildroot, board, chrome_atom_to_build):
   """Wrapper for emerge call to build Chrome."""
   cwd = os.path.join(buildroot, 'src', 'scripts')
   RunCommand(['emerge-%s' % board, '=%s' % chrome_atom_to_build],
              cwd=cwd, enter_chroot=True)
 
 
 def _EnableLocalAccount(buildroot):
@@ skipping 281 matching lines @@
     chroot_path = os.path.join(buildroot, 'chroot')
     boardpath = os.path.join(chroot_path, 'build', board)
     if options.sync:
       if options.clobber or not os.path.isdir(buildroot):
         _FullCheckout(buildroot, tracking_branch, url=options.url)
       else:
         old_binhost = _GetPortageEnvVar(buildroot, board, _FULL_BINHOST)
         _IncrementalCheckout(buildroot)
 
     new_binhost = _GetPortageEnvVar(buildroot, board, _FULL_BINHOST)
-    if old_binhost and old_binhost != new_binhost:
-      RunCommand(['sudo', 'rm', '-rf', boardpath])
+    emptytree = (old_binhost and old_binhost != new_binhost)
 
     # Check that all overlays can be found.
     for path in rev_overlays:
       if not os.path.isdir(path):
         Die('Missing overlay: %s' % path)
 
     if not os.path.isdir(chroot_path):
       _MakeChroot(buildroot)
 
     if not os.path.isdir(boardpath):
       _SetupBoard(buildroot, board=buildconfig['board'])
 
     # Perform uprev.  If chrome_uprev is set, rev Chrome ebuilds.
     if options.chrome_rev:
       chrome_atom_to_build = _MarkChromeAsStable(buildroot, tracking_branch,
                                                  options.chrome_rev)
     elif buildconfig['uprev']:
       _UprevPackages(buildroot, tracking_branch, revisionfile,
                      buildconfig['board'], rev_overlays)
 
     _EnableLocalAccount(buildroot)
     # Doesn't rebuild without acquiring more source.
     if options.sync:
-      _Build(buildroot)
+      _Build(buildroot, emptytree)
 
     if chrome_atom_to_build:
       _BuildChrome(buildroot, buildconfig['board'], chrome_atom_to_build)
 
     if buildconfig['unittests'] and options.tests:
       _RunUnitTests(buildroot)
 
     _BuildImage(buildroot)
 
     if buildconfig['smoke_bvt'] and options.tests:
@@ skipping 32 matching lines @@
   except:
     # Send failure to master bot.
     if not buildconfig['master'] and buildconfig['important']:
       cbuildbot_comm.PublishStatus(cbuildbot_comm.STATUS_BUILD_FAILED)
 
     raise
 
 
 if __name__ == '__main__':
     main()