Cross-platform plumbing for resize-to-client

remoting/host/desktop_resizer_linux.cc

+// 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.
+
+#include "remoting/host/desktop_resizer.h"
+
+#include <X11/Xlib.h>
+#include <X11/extensions/Xrandr.h>
+
+#include "base/logging.h"
+
+// On Linux, we use the xrandr extension to change the desktop size. This has
+// a number of quirks that make the code more complex:
+//
+//   1. It's not possible to change the size of an existing mode. Instead, the
+//      mode must be deleted and recreated.
+//   2. It's not possible to delete a mode that's in use.
+//   3. Errors are communicated via Xlib's spectacularly unhelpful mechanism
+//      of terminating the process unless you install an error handler.
+//
+// The basic approach is to create a new mode with the correct size, switch to
+// it, then delete the old one. Since the new mode must have a different name,
+// and we want the current mode name to be consistent, we then recreate the old
+// mode at the new size, switch to it and delete the temporary. The reason for
+// name consistency is to allow a future CL to disable resize-to-client if the
+// user has changed the mode to something other than "Chrome Remote Desktop
+// client size"). It doesn't make the code significantly more complex.

[rmsousa, 2012/09/13 21:59:05]

Nit:Stray )

[Jamie, 2012/09/14 21:07:34]

Done.

+
+namespace remoting {
+
+namespace {
+// Temporarily install an alternative handler for X errors. The default handler
+// exits the process, which is not what we want.
+// TODO(jamiewalch): This doesn't really belong here, and should provide some
+// means of checking whether or not anything went wrong.
+class ScopedXErrorHandler {
+ public:
+  typedef int (*Handler)(Display*, XErrorEvent*);
+  ScopedXErrorHandler(Handler handler) {
+    previous_handler_ = XSetErrorHandler(handler);
+  }
+  ~ScopedXErrorHandler() {
+    XSetErrorHandler(previous_handler_);
+  }
+
+  static int Ignore(Display* display, XErrorEvent* event) {
+    LOG(INFO) << "Ignoring error.";
+    return 0;
+  }
+
+ private:
+  Handler previous_handler_;
+};
+
+class ScopedXGrabServer {
+ public:
+  ScopedXGrabServer(Display* display)
+      : display_(display) {
+    XGrabServer(display_);
+  }
+  ~ScopedXGrabServer() {
+    XUngrabServer(display_);
+    XFlush(display_);
+  }
+ private:
+  Display* display_;
+};
+
+// Wrapper class for the XRRScreenResources struct.
+class ScreenResources {
+ public:
+  ScreenResources() : resources_(NULL) {
+  }
+
+  ~ScreenResources() {
+    Release();
+  }
+
+  bool Refresh(Display* display, Window window) {
+    Release();
+    resources_ = XRRGetScreenResources(display, window);
+    return resources_ != NULL;
+  }
+
+  void Release() {
+    if (resources_) {
+      XRRFreeScreenResources(resources_);
+      resources_ = NULL;
+    }
+  }
+
+  RRMode GetIdForMode(const char* name) {
+    CHECK(resources_);
+    for (int i = 0; i < resources_->nmode; ++i) {
+      const XRRModeInfo& mode = resources_->modes[i];
+      if (strcmp(mode.name, name) == 0) {
+        return mode.id;
+      }
+    }
+    return 0;
+  }
+
+  // For now, assume we're only ever interested in the first output.
+  RROutput GetOutput() {
+    CHECK(resources_);
+    return resources_->outputs[0];
+  }
+
+  // For now, assume we're only ever interested in the first crtc.
+  RRCrtc GetCrtc() {
+    CHECK(resources_);
+    return resources_->crtcs[0];
+  }
+
+  XRROutputInfo* GetOutputInfo(Display* display, RROutput output_id) {
+    CHECK(resources_);
+    return XRRGetOutputInfo(display, resources_, output_id);
+  }
+
+  XRRScreenResources* get() { return resources_; }
+
+ private:
+  XRRScreenResources* resources_;
+};
+
+
+class DesktopResizerLinux : public DesktopResizer {
+ public:
+  DesktopResizerLinux();
+  virtual ~DesktopResizerLinux();
+
+  // DesktopResizer interface
+  virtual SkISize GetSize() OVERRIDE;
+  virtual void SetSize(const SkISize& size) OVERRIDE;
+
+ private:
+  // Create a mode, and attach it to the primary output. If the mode already
+  // exists, it is left unchanged.
+  void CreateMode(const char* name, int width, int height);
+
+  // Remove the specified mode from the primary output, and delete it. If the
+  // mode is in use, it is not deleted.
+  void DeleteMode(const char* name);
+
+  // Switch the primary output to the specified mode.
+  void SwitchToMode(const char* name);
+
+  Display* display_;
+  Window root_;
+  ScreenResources resources_;
+
+  DISALLOW_COPY_AND_ASSIGN(DesktopResizerLinux);
+};
+}  // namespace
+
+DesktopResizerLinux::DesktopResizerLinux()
+    : display_(XOpenDisplay(NULL)),
+      root_(RootWindow(display_, DefaultScreen(display_))) {
+}
+
+DesktopResizerLinux::~DesktopResizerLinux() {
+  XCloseDisplay(display_);
+}
+
+SkISize DesktopResizerLinux::GetSize() {
+  ScopedXErrorHandler handler(ScopedXErrorHandler::Ignore);
+  SkISize result = SkISize::Make(0, 0);
+  int num_sizes;
+  XRRScreenSize *sizes = XRRSizes(display_, 0, &num_sizes);
+  // If xrandr is not supported, num_sizes is set to zero.
+  if (num_sizes) {
+    XRRScreenConfiguration *config = XRRGetScreenInfo(display_, root_);
+    Rotation rotation;
+    SizeID size_id = XRRConfigCurrentConfiguration(config, &rotation);
+    CHECK(size_id < num_sizes);
+    result = SkISize::Make(sizes[size_id].width, sizes[size_id].height);
+  }
+  return result;
+}
+
+void DesktopResizerLinux::SetSize(const SkISize& size) {
+  // Ignore X errors encountered while resizing the display. We might hit an
+  // error, for example if xrandr has been used to add a mode with the same
+  // name as our temporary mode, or to remove the "client size" mode. We don't
+  // want to terminate the process if this happens.
+  ScopedXErrorHandler handler(ScopedXErrorHandler::Ignore);
+
+  // Grab the X server while we're changing the display size. This ensures
+  // that the display configuration doesn't change under our feet.
+  ScopedXGrabServer grabber(display_);
+
+  // Clamp the specified size to something valid for the X server.
+  int width = size.width(), height = size.height();
+  int min_width = 0, min_height = 0, max_width = 0, max_height = 0;
+  XRRGetScreenSizeRange(display_, root_,
+                        &min_width, &min_height,
+                        &max_width, &max_height);
+  if (size.width() < min_width) {
+    width = min_width;
+  } else if (width > max_width) {
+    width = max_width;
+  }
+  if (height < min_height) {
+    height = min_height;
+  } else if (height > max_height) {
+    height = max_height;
+  }
+  LOG(INFO) << "Changing desktop size to " << width << "x" << height;
+
+  // The name of the mode representing the current client view size and the
+  // temporary mode used for the reasons described at the top of this file.
+  // The former should be localized if it's user-visible; the latter only
+  // exists briefly and does not need to localized.
+  const char* kModeName = "Chrome Remote Desktop client size";
+  const char* kTempModeName = "Chrome Remote Desktop temporary mode";
+
+  // Actually do the resize operation, preserving the current mode name. Note
+  // that we have to detatch the output from any mode in order to resize it
+  // (strictly speaking, this is only required when reducing the size, but it
+  // seems safe to do it regardless).
+  CreateMode(kTempModeName, width, height);
+  SwitchToMode(NULL);
+  XRRSetScreenSize(display_, root_, width, height, -1, -1);
+  SwitchToMode(kTempModeName);
+  DeleteMode(kModeName);
+  CreateMode(kModeName, width, height);
+  SwitchToMode(kModeName);
+  DeleteMode(kTempModeName);
+}
+
+void DesktopResizerLinux::CreateMode(const char* name, int width, int height) {
+  XRRModeInfo mode;

[rmsousa, 2012/09/13 21:59:05]

These all-zero modes are only valid for Xvfb. Do we care about me2me to non-Xvfb
displays?

[Jamie, 2012/09/14 21:07:34]

Good point. I'll add some code to explicitly check for Xvfb-randr; for other X
servers we'll want a different algorithm anyway, so I'll disable resize for now.

[rmsousa, 2012/09/14 21:37:05]

Do you know any way to do that check reliably? If you do, can you make that a
separate class (as I'll also need it for the curtain mode enforcement)

FWIW, I couldn't find any way to directly test it... so I was going with the
approach in http://codereview.chromium.org/10914298/patch/1/4, but that's fairly
hacky (and I'm not sure if it fits here)

In your particular case, I figure testing if the current mode is already
all-zeroes should be enough for safety (even if it doesn't directly test for
xvfb).

+  memset(&mode, 0, sizeof(mode));
+  mode.width = width;
+  mode.height = height;
+  mode.name = const_cast<char*>(name);
+  mode.nameLength = strlen(name);
+  XRRCreateMode(display_, root_, &mode);
+
+  if (!resources_.Refresh(display_, root_)) {
+    return;
+  }
+  RRMode mode_id = resources_.GetIdForMode(name);
+  if (!mode_id) {
+    return;
+  }
+  XRRAddOutputMode(display_, resources_.GetOutput(), mode_id);
+}
+
+void DesktopResizerLinux::DeleteMode(const char* name) {
+  RRMode mode_id = resources_.GetIdForMode(name);
+  if (mode_id) {
+    XRRDeleteOutputMode(display_, resources_.GetOutput(), mode_id);
+    XRRDestroyMode(display_, mode_id);
+    resources_.Refresh(display_, root_);
+  }
+}
+
+void DesktopResizerLinux::SwitchToMode(const char* name) {
+  RRMode mode_id = None;
+  RROutput* outputs = NULL;
+  int number_of_outputs = 0;
+  if (name) {
+    mode_id = resources_.GetIdForMode(name);
+    CHECK(mode_id);
+    outputs = resources_.get()->outputs;
+    number_of_outputs = resources_.get()->noutput;
+  }
+  XRRSetCrtcConfig(display_, resources_.get(), resources_.GetCrtc(),
+                   CurrentTime, 0, 0, mode_id, 1, outputs, number_of_outputs);
+}
+
+scoped_ptr<DesktopResizer> DesktopResizer::Create() {
+  return scoped_ptr<DesktopResizer>(new DesktopResizerLinux);
+}
+
+}  // namespace remoting