Update cbuildbot.py and prebuilt.py to deduplicate preflight prebuilts.

bin/cbuildbot.py

Index: bin/cbuildbot.py
diff --git a/bin/cbuildbot.py b/bin/cbuildbot.py
index 0c2f2eaa4f4a1a7e8aecafdd46ef6f14b5a98ca2..b73a72409ffa5bddc3214fc0a38ec7d0d025c9a5 100755
--- a/bin/cbuildbot.py
+++ b/bin/cbuildbot.py
@@ -310,17 +310,20 @@ def _GetPortageEnvVar(buildroot, board, envvar):
 
   buildroot: The root directory where the build occurs. Must be an absolute
              path.
-  board: Board type that was built on this machine. E.g. x86-generic.
-  envvar: The environment variable to get. E.g. "PORTAGE_BINHOST".
+  board: Board type that was built on this machine. E.g. x86-generic. If this
+         is None, get the env var from the host.
+  envvar: The environment variable to get. E.g. 'PORTAGE_BINHOST'.
 
   Returns:
     The value of the environment variable, as a string. If no such variable
     can be found, return the empty string.
   """
   cwd = os.path.join(buildroot, 'src', 'scripts')
-  binhost = RunCommand(['portageq-%s' % board, 'envvar', envvar],
-                       cwd=cwd, redirect_stdout=True, enter_chroot=True,
-                       error_ok=True)
+  portageq = 'portageq'
+  if board:
+    portageq += '-%s' % board
+  binhost = RunCommand([portageq, 'envvar', envvar], cwd=cwd,
+                       redirect_stdout=True, enter_chroot=True, error_ok=True)
   return binhost.rstrip('\n')
 
 
@@ -522,7 +525,7 @@ def _ResolveOverlays(buildroot, overlays):
   return paths
 
 
-def _UploadPrebuilts(buildroot, board, overlay_config):
+def _UploadPrebuilts(buildroot, board, overlay_config, binhosts):
   """Upload prebuilts.
 
   Args:
@@ -532,14 +535,20 @@ def _UploadPrebuilts(buildroot, board, overlay_config):
                     'private': Just the private overlay.
                     'public': Just the public overlay.
                     'both': Both the public and private overlays.
+    binhosts: The URLs of the current binhosts. Binaries that are already
+              present will not be uploaded twice. Empty URLs will be ignored.
   """
 
   cmd = ['%s/src/scripts/prebuilt.py' % buildroot,
          '--sync-binhost-conf',
+         '--sync-host',
          '--build-path', buildroot,
          '--board', board,
          '--prepend-version', 'preflight',
          '--key', _PREFLIGHT_BINHOST]
+  for binhost in binhosts:
+    if binhost:
+      cmd.extend(['--previous-binhost-url', binhost])
   if overlay_config == 'public':
     cmd.extend(['--upload', 'gs://chromeos-prebuilt'])
   else:
@@ -595,12 +604,14 @@ def main():
     boardpath = os.path.join(chroot_path, 'build', board)
     if options.clobber or not os.path.isdir(buildroot):
       _FullCheckout(buildroot, tracking_branch, url=options.url)
+      new_binhost = _GetPortageEnvVar(buildroot, board, _FULL_BINHOST),
     else:
       old_binhost = _GetPortageEnvVar(buildroot, board, _FULL_BINHOST)
       _IncrementalCheckout(buildroot)
       new_binhost = _GetPortageEnvVar(buildroot, board, _FULL_BINHOST)
       if old_binhost != new_binhost:
         RunCommand(['sudo', 'rm', '-rf', boardpath])
+    binhosts = [new_binhost, _GetPortageEnvVar(buildroot, None, _FULL_BINHOST)]
 
     # Check that all overlays can be found.
     for path in overlays:
@@ -641,7 +652,8 @@ def main():
         if buildconfig['master']:
           # Master bot needs to check if the other slaves completed.
           if cbuildbot_comm.HaveSlavesCompleted(config):
-            _UploadPrebuilts(buildroot, board, buildconfig['overlays'])
+            _UploadPrebuilts(buildroot, board, buildconfig['overlays'],
+                             binhosts)
             _UprevPush(buildroot, tracking_branch, buildconfig['board'],
                        overlays)
           else: