Add Xorg+dummy as alternative for Xvfb

remoting/host/linux/linux_me2me_host.py

 #!/usr/bin/python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Virtual Me2Me implementation.  This script runs and manages the processes
 # required for a Virtual Me2Me desktop, which are: X server, X desktop
 # session, and Host process.
 # This script is intended to run continuously as a background daemon
 # process, running under an ordinary (non-root) user account.
@@ skipping 24 matching lines @@
 import time
 import uuid
 
 LOG_FILE_ENV_VAR = "CHROME_REMOTE_DESKTOP_LOG_FILE"
 
 # This script has a sensible default for the initial and maximum desktop size,
 # which can be overridden either on the command-line, or via a comma-separated
 # list of sizes in this environment variable.
 DEFAULT_SIZES_ENV_VAR = "CHROME_REMOTE_DESKTOP_DEFAULT_DESKTOP_SIZES"
 
+# By default, this script launches Xvfb as the virtual X display. When this
+# environment variable is set, the script will instead launch an instance of
+# Xorg using the dummy display driver and void input device. In order for this
+# to work, both the dummy display driver and void input device need to be
+# installed:
+#
+#     sudo apt-get install xserver-xorg-video-dummy
+#     sudo apt-get install xserver-xorg-input-void

[Lambros, 2016/05/10 21:06:57]

This is OK for now, but when we make Xorg+dummy the default, we should add these
as Debian package dependencies.

[rkjnsn, 2016/05/10 21:38:03]

Certainly. Should I add a TODO?

+USE_XORG_ENV_VAR = "CHROME_REMOTE_DESKTOP_USE_XORG"
+
+# The amount of video RAM the dummy driver should claim to have, which limits
+# the maximum possible resolution.
+# 1048576 KiB = 1 GiB, which is the amount of video RAM needed to have a
+# 16384x16384 pixel frame buffer (the maximum size supported by VP8) with 32
+# bits per pixel.
+XORG_DUMMY_VIDEO_RAM = 1048576 # KiB
+
 # By default, provide a maximum size that is large enough to support clients
 # with large or multiple monitors. This is a comma-separated list of
 # resolutions that will be made available if the X server supports RANDR. These
 # defaults can be overridden in ~/.profile.
 DEFAULT_SIZES = "1600x1200,3840x2560"
 
 # If RANDR is not available, use a smaller default size. Only a single
 # resolution is supported in this case.
 DEFAULT_SIZE_NO_RANDR = "1600x1200"
 
@@ skipping 27 matching lines @@
 
 # Thresholds for switching from fast- to slow-restart and for giving up
 # trying to restart entirely.
 SHORT_BACKOFF_THRESHOLD = 5
 MAX_LAUNCH_FAILURES = SHORT_BACKOFF_THRESHOLD + 10
 
 # Globals needed by the atexit cleanup() handler.
 g_desktops = []
 g_host_hash = hashlib.md5(socket.gethostname()).hexdigest()
 
+def gen_xorg_config(sizes):
+  return (
+      # This causes X to load the default GLX module, even if a proprietary one
+      # is installed in a different directory.
+      'Section "Files"\n'
+      '  ModulePath "/usr/lib/xorg/modules"\n'
+      'EndSection\n'
+      '\n'
+      # Suppress device probing, which happens by default.
+      'Section "ServerFlags"\n'
+      '  Option "AutoAddDevices" "false"\n'
+      '  Option "AutoEnableDevices" "false"\n'
+      '  Option "DontVTSwitch" "true"\n'
+      '  Option "PciForceNone" "true"\n'
+      'EndSection\n'
+      '\n'
+      'Section "InputDevice"\n'
+      # The host looks for this name to check whether it's running in a virtual
+      # session
+      '  Identifier "Chrome Remote Desktop Input"\n'
+      # While the xorg.conf man page specifies that both of these options are
+      # deprecated synonyms for `Option "Floating" "false"`, it turns out that
+      # if both aren't specified, the Xorg server will automatically attempt to
+      # add additional devices.
+      '  Option "CoreKeyboard" "true"\n'
+      '  Option "CorePointer" "true"\n'
+      '  Driver "void"\n'
+      'EndSection\n'
+      '\n'
+      'Section "Device"\n'
+      '  Identifier "Chrome Remote Desktop Videocard"\n'
+      '  Driver "dummy"\n'
+      '  VideoRam {video_ram}\n'
+      'EndSection\n'
+      '\n'
+      'Section "Monitor"\n'
+      '  Identifier "Chrome Remote Desktop Monitor"\n'
+      # The horizontal sync rate was calculated from the vertical refresh rate
+      # and the modline template:
+      # (33000 (vert total) * 0.1 Hz = 3.3 kHz)
+      '  HorizSync   3.3\n' # kHz
+      # The vertical refresh rate was chosen both to be low enough to have an
+      # acceptable dot clock at high resolutions, and then bumped down a little
+      # more so that in the unlikely event that a low refresh rate would break
+      # something, it would break obviously.
+      '  VertRefresh 0.1\n' # Hz
+      '{modelines}'
+      'EndSection\n'
+      '\n'
+      'Section "Screen"\n'
+      '  Identifier "Chrome Remote Desktop Screen"\n'
+      '  Device "Chrome Remote Desktop Videocard"\n'
+      '  Monitor "Chrome Remote Desktop Monitor"\n'
+      '  DefaultDepth 24\n'
+      '  SubSection "Display"\n'
+      '    Viewport 0 0\n'
+      '    Depth 24\n'
+      '    Modes {modes}\n'
+      '  EndSubSection\n'
+      'EndSection\n'
+      '\n'
+      'Section "ServerLayout"\n'
+      '  Identifier   "Chrome Remote Desktop Layout"\n'
+      '  Screen       "Chrome Remote Desktop Screen"\n'
+      '  InputDevice  "Chrome Remote Desktop Input"\n'
+      'EndSection\n'.format(
+          # This Modeline template allows resolutions up to the dummy driver's
+          # max supported resolution of 32767x32767 without additional
+          # calculation while meeting the driver's dot clock requirements. Note
+          # that VP8 (and thus the amount of video RAM chosen) only support a
+          # maximum resolution of 16384x16384.
+          # 32767x32767 should be possible if we switch fully to VP9 and
+          # increase the video RAM to 4GiB.
+          # The dot clock was calculated to match the VirtRefresh chosen above.
+          # (33000 * 33000 * 0.1 Hz = 108.9 MHz)
+          # Changes this line require matching changes to HorizSync and
+          # VertRefresh.
+          modelines="".join(
+              '  Modeline "{0}x{1}" 108.9 {0} 32998 32999 33000 '
+              '{1} 32998 32999 33000\n'.format(w, h) for w, h in sizes),
+          modes=" ".join('"{0}x{1}"'.format(w, h) for w, h in sizes),
+          video_ram=XORG_DUMMY_VIDEO_RAM))
+
 
 def is_supported_platform():
   # Always assume that the system is supported if the config directory or
   # session file exist.
   if (os.path.isdir(CONFIG_DIR) or os.path.isfile(SESSION_FILE_PATH) or
       os.path.isfile(SYSTEM_SESSION_FILE_PATH)):
     return True
 
   # The host has been tested only on Ubuntu.
   distribution = platform.linux_distribution()
   return (distribution[0]).lower() == 'ubuntu'
 
 
-def get_randr_supporting_x_server():
-  """Returns a path to an X server that supports the RANDR extension, if this
-  is found on the system. Otherwise returns None."""
+def locate_xvfb_randr():
+  """Returns a path to our RANDR-supporting Xvfb server, if it is found on the
+  system. Otherwise returns None."""
 
   xvfb = "/usr/bin/Xvfb-randr"
   if os.path.exists(xvfb):
     return xvfb
 
   xvfb = os.path.join(SCRIPT_DIR, "Xvfb-randr")
   if os.path.exists(xvfb):
     return xvfb
 
   return None
@@ skipping 113 matching lines @@
 
 class Desktop:
   """Manage a single virtual desktop"""
 
   def __init__(self, sizes):
     self.x_proc = None
     self.session_proc = None
     self.host_proc = None
     self.child_env = None
     self.sizes = sizes
+    self.xorg_conf = None
     self.pulseaudio_pipe = None
     self.server_supports_exact_resize = False
     self.host_ready = False
     self.ssh_auth_sockname = None
     g_desktops.append(self)
 
   @staticmethod
   def get_unused_display_number():
     """Return a candidate display number for which there is currently no
     X Server lock file"""
@@ skipping 98 matching lines @@
     self.child_env["PULSE_STATE_PATH"] = pulse_path
     self.child_env["PULSE_SINK"] = sink_name
     self.pulseaudio_pipe = pipe_name
 
     return True
 
   def _setup_gnubby(self):
     self.ssh_auth_sockname = ("/tmp/chromoting.%s.ssh_auth_sock" %
                               os.environ["USER"])
 
+  def _launch_xvfb(self, display, x_auth_file, extra_x_args):
+    max_width = max([width for width, height in self.sizes])
+    max_height = max([height for width, height in self.sizes])
+
+    xvfb = locate_xvfb_randr()
+    if xvfb:
+      self.server_supports_exact_resize = True
+    else:
+      xvfb = "Xvfb"
+      self.server_supports_exact_resize = False
+
+    logging.info("Starting %s on display :%d" % (xvfb, display))
+    screen_option = "%dx%dx24" % (max_width, max_height)
+    self.x_proc = subprocess.Popen(
+        [xvfb, ":%d" % display,
+         "-auth", x_auth_file,
+         "-nolisten", "tcp",
+         "-noreset",
+         "-screen", "0", screen_option
+        ] + extra_x_args)
+    if not self.x_proc.pid:
+      raise Exception("Could not start Xvfb.")
+
+  def _launch_xorg(self, display, x_auth_file, extra_x_args):
+    with tempfile.NamedTemporaryFile(
+        prefix="chrome_remote_desktop_",
+        suffix=".conf", delete=False) as config_file:
+      config_file.write(gen_xorg_config(self.sizes))
+
+    # For now, we don't support exact resize with Xorg+dummy
+    self.server_supports_exact_resize = False
+    self.xorg_conf = config_file.name
+
+    logging.info("Starting Xorg on display :%d" % display)
+    # We use the child environment so the Xorg server picks up the Mesa libGL
+    # instead of any proprietary versions that may be installed, thanks to
+    # LD_LIBRARY_PATH.
+    # Note: This prevents any environment variable the user has set from
+    # affecting the Xorg server.
+    self.x_proc = subprocess.Popen(
+        ["Xorg", ":%d" % display,
+         "-auth", x_auth_file,
+         "-nolisten", "tcp",
+         "-noreset",
+         # Disable logging to a file and instead bump up the stderr verbosity
+         # so the equivalent information gets logged in our main log file.
+         "-logfile", "/dev/null",
+         "-verbose", "3",
+         "-config", config_file.name
+        ] + extra_x_args, env=self.child_env)
+    if not self.x_proc.pid:
+      raise Exception("Could not start Xorg.")
+
   def _launch_x_server(self, extra_x_args):
     x_auth_file = os.path.expanduser("~/.Xauthority")
     self.child_env["XAUTHORITY"] = x_auth_file
     devnull = open(os.devnull, "r+")
     display = self.get_unused_display_number()
 
     # Run "xauth add" with |child_env| so that it modifies the same XAUTHORITY
     # file which will be used for the X session.
     ret_code = subprocess.call("xauth add :%d . `mcookie`" % display,
                                env=self.child_env, shell=True)
     if ret_code != 0:
       raise Exception("xauth failed with code %d" % ret_code)
 
-    max_width = max([width for width, height in self.sizes])
-    max_height = max([height for width, height in self.sizes])
-
-    xvfb = get_randr_supporting_x_server()
-    if xvfb:
-      self.server_supports_exact_resize = True
-    else:
-      xvfb = "Xvfb"
-      self.server_supports_exact_resize = False
-
     # Disable the Composite extension iff the X session is the default
     # Unity-2D, since it uses Metacity which fails to generate DAMAGE
     # notifications correctly. See crbug.com/166468.
     x_session = choose_x_session()
     if (len(x_session) == 2 and
         x_session[1] == "/usr/bin/gnome-session --session=ubuntu-2d"):
       extra_x_args.extend(["-extension", "Composite"])
 
-    logging.info("Starting %s on display :%d" % (xvfb, display))
-    screen_option = "%dx%dx24" % (max_width, max_height)
-    self.x_proc = subprocess.Popen(
-        [xvfb, ":%d" % display,
-         "-auth", x_auth_file,
-         "-nolisten", "tcp",
-         "-noreset",
-         "-screen", "0", screen_option
-        ] + extra_x_args)
-    if not self.x_proc.pid:
-      raise Exception("Could not start Xvfb.")
+    if USE_XORG_ENV_VAR in os.environ:
+      self._launch_xorg(display, x_auth_file, extra_x_args)
+    else:
+      self._launch_xvfb(display, x_auth_file, extra_x_args)
 
     self.child_env["DISPLAY"] = ":%d" % display
     self.child_env["CHROME_REMOTE_DESKTOP_SESSION"] = "1"
 
     # Use a separate profile for any instances of Chrome that are started in
     # the virtual session. Chrome doesn't support sharing a profile between
     # multiple DISPLAYs, but Chrome Sync allows for a reasonable compromise.
     chrome_profile = os.path.join(CONFIG_DIR, "chrome-profile")
     self.child_env["CHROME_USER_DATA_DIR"] = chrome_profile
 
     # Set SSH_AUTH_SOCK to the file name to listen on.
     if self.ssh_auth_sockname:
       self.child_env["SSH_AUTH_SOCK"] = self.ssh_auth_sockname
 
     # Wait for X to be active.
     for _test in range(20):
       retcode = subprocess.call("xdpyinfo", env=self.child_env, stdout=devnull)
       if retcode == 0:
         break
       time.sleep(0.5)
     if retcode != 0:
-      raise Exception("Could not connect to Xvfb.")
+      raise Exception("Could not connect to X server.")
     else:
-      logging.info("Xvfb is active.")
+      logging.info("X server is active.")
 
     # The remoting host expects the server to use "evdev" keycodes, but Xvfb
     # starts configured to use the "base" ruleset, resulting in XKB configuring
     # for "xfree86" keycodes, and screwing up some keys. See crbug.com/119013.
     # Reconfigure the X server to use "evdev" keymap rules.  The X server must
     # be started with -noreset otherwise it'll reset as soon as the command
     # completes, since there are no other X clients running yet.
     retcode = subprocess.call("setxkbmap -rules evdev", env=self.child_env,
                               shell=True)
     if retcode != 0:
@@ skipping 389 matching lines @@
   # Close the temporary file-descriptors.
   os.close(devnull_fd)
   os.close(log_fd)
 
 
 def cleanup():
   logging.info("Cleanup.")
 
   global g_desktops
   for desktop in g_desktops:
-    for proc, name in [(desktop.x_proc, "Xvfb"),
+    for proc, name in [(desktop.x_proc, "X server"),
                        (desktop.session_proc, "session"),
                        (desktop.host_proc, "host")]:
       if proc is not None:
         logging.info("Terminating " + name)
         try:
           psutil_proc = psutil.Process(proc.pid)
           psutil_proc.terminate()
 
           # Use a short timeout, to avoid delaying service shutdown if the
           # process refuses to die for some reason.
           psutil_proc.wait(timeout=10)
         except psutil.TimeoutExpired:
           logging.error("Timed out - sending SIGKILL")
           psutil_proc.kill()
         except psutil.Error:
           logging.error("Error terminating process")
+    if desktop.xorg_conf is not None:
+      os.remove(desktop.xorg_conf)
 
   g_desktops = []
   if ParentProcessLogger.instance():
     ParentProcessLogger.instance().release_parent(False)
 
 class SignalHandler:
   """Reload the config file on SIGHUP. Since we pass the configuration to the
   host processes via stdin, they can't reload it, so terminate them. They will
   be relaunched automatically with the new config."""
 
@@ skipping 180 matching lines @@
 def main():
   EPILOG = """This script is not intended for use by end-users.  To configure
 Chrome Remote Desktop, please install the app from the Chrome
 Web Store: https://chrome.google.com/remotedesktop"""
   parser = optparse.OptionParser(
       usage="Usage: %prog [options] [ -- [ X server options ] ]",
       epilog=EPILOG)
   parser.add_option("-s", "--size", dest="size", action="append",
                     help="Dimensions of virtual desktop. This can be specified "
                     "multiple times to make multiple screen resolutions "
-                    "available (if the Xvfb server supports this).")
+                    "available (if the X server supports this).")
   parser.add_option("-f", "--foreground", dest="foreground", default=False,
                     action="store_true",
                     help="Don't run as a background daemon.")
   parser.add_option("", "--start", dest="start", default=False,
                     action="store_true",
                     help="Start the host.")
   parser.add_option("-k", "--stop", dest="stop", default=False,
                     action="store_true",
                     help="Stop the daemon currently running.")
   parser.add_option("", "--get-status", dest="get_status", default=False,
@@ skipping 113 matching lines @@
     watch_for_resolution_changes(options.watch_resolution)
     return 0
 
   if not options.start:
     # If no modal command-line options specified, print an error and exit.
     print(EPILOG, file=sys.stderr)
     return 1
 
   # If a RANDR-supporting Xvfb is not available, limit the default size to
   # something more sensible.
-  if get_randr_supporting_x_server():
+  if USE_XORG_ENV_VAR not in os.environ and locate_xvfb_randr():
     default_sizes = DEFAULT_SIZES
   else:
     default_sizes = DEFAULT_SIZE_NO_RANDR
 
   # Collate the list of sizes that XRANDR should support.
   if not options.size:
     if DEFAULT_SIZES_ENV_VAR in os.environ:
       default_sizes = os.environ[DEFAULT_SIZES_ENV_VAR]
     options.size = default_sizes.split(",")
 
@@ skipping 180 matching lines @@
         else:
           logging.info("Host exited with status %s." % os.WEXITSTATUS(status))
       elif os.WIFSIGNALED(status):
         logging.info("Host terminated by signal %s." % os.WTERMSIG(status))
 
 
 if __name__ == "__main__":
   logging.basicConfig(level=logging.DEBUG,
                       format="%(asctime)s:%(levelname)s:%(message)s")
   sys.exit(main())