evdev: Support device hotplug with udev

ui/events/ozone/evdev/device_manager_udev.cc

+// Copyright 2014 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 "ui/events/ozone/evdev/device_manager_udev.h"
+
+#include <libudev.h>
+
+#include "base/files/file_path.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/message_loop/message_pump_ozone.h"
+#include "base/strings/stringprintf.h"
+#include "ui/events/ozone/evdev/event_factory.h"
+#include "ui/events/ozone/evdev/scoped_udev.h"
+
+namespace ui {
+
+namespace {
+
+const char kSubsystemInput[] = "input";
+
+// Severity levels from syslog.h. We can't include it directly as it
+// conflicts with base/logging.h
+enum {
+  SYS_LOG_EMERG = 0,
+  SYS_LOG_ALERT = 1,
+  SYS_LOG_CRIT = 2,
+  SYS_LOG_ERR = 3,
+  SYS_LOG_WARNING = 4,
+  SYS_LOG_NOTICE = 5,
+  SYS_LOG_INFO = 6,
+  SYS_LOG_DEBUG = 7,
+};
+
+// Log handler for messages generated from libudev.
+void UdevLog(struct udev* udev,
+             int priority,
+             const char* file,
+             int line,
+             const char* fn,
+             const char* format,
+             va_list args) {
+  std::string message = base::StringPrintf("libudev: %s: ", fn);
+  base::StringAppendV(&message, format, args);
+  if (priority <= SYS_LOG_ERR)
+    LOG(ERROR) << message;
+  else if (priority <= SYS_LOG_INFO)
+    VLOG(1) << message;
+  else  // SYS_LOG_DEBUG

[rjkroege, 2014/02/03 15:36:55]

nit: i think that it might be more chrome-y to return early and discard the
else. Or maybe I'm channeling webkit style. 

[spang, 2014/02/03 16:43:32]

If you have a less vague consistency argument I will change it. I like this more
symmetrical way.

+    VLOG(2) << message;
+}
+
+// Create libudev context.
+scoped_udev UdevCreate() {
+  struct udev* udev = udev_new();
+  if (udev) {
+    udev_set_log_fn(udev, UdevLog);
+    udev_set_log_priority(udev, SYS_LOG_DEBUG);
+  }
+  return scoped_udev(udev);
+}
+
+// Start monitoring input device changes.
+scoped_udev_monitor UdevCreateMonitor(struct udev* udev) {
+  struct udev_monitor* monitor = udev_monitor_new_from_netlink(udev, "udev");
+  if (monitor) {
+    udev_monitor_filter_add_match_subsystem_devtype(
+        monitor, kSubsystemInput, NULL);
+
+    if (udev_monitor_enable_receiving(monitor))
+      LOG(ERROR) << "failed to start receiving events from udev";
+  }
+
+  return scoped_udev_monitor(monitor);
+}
+
+// Enumerate all input devices using udev. Calls device_callback per device.
+bool UdevEnumerateInputDevices(struct udev* udev,
+                               const EvdevDeviceCallback& device_callback) {
+  scoped_udev_enumerate enumerate(udev_enumerate_new(udev));
+  if (!enumerate)
+    return false;
+
+  // Build list of devices with subsystem "input".
+  udev_enumerate_add_match_subsystem(enumerate.get(), kSubsystemInput);
+  udev_enumerate_scan_devices(enumerate.get());
+
+  struct udev_list_entry* devices =
+      udev_enumerate_get_list_entry(enumerate.get());
+  struct udev_list_entry* entry;
+
+  // Run callback per device in the list.
+  udev_list_entry_foreach(entry, devices) {

[rjkroege, 2014/02/03 15:36:55]

this is a macro?

[spang, 2014/02/03 16:43:32]

Yes.

+    const char* name = udev_list_entry_get_name(entry);
+
+    scoped_udev_device device(udev_device_new_from_syspath(udev, name));
+    if (!device)
+      continue;
+
+    const char* path = udev_device_get_devnode(device.get());
+    if (!path)
+      continue;
+
+    // Found input device node; attach.
+    device_callback.Run(base::FilePath(path));
+  }
+
+  return true;
+}
+
+// Device enumerator & monitor using udev.
+//
+// This class enumerates input devices attached to the system using udev.
+//
+// It also creates & monitors a udev netlink socket and issues callbacks for

[rjkroege, 2014/02/03 15:36:55]

what thread does this class run on? hopefully not the UI thread. 

[spang, 2014/02/03 16:43:32]

UI thread. Would like to land the single-threaded version first.

+// any changes to the set of attached devices.
+class DeviceManagerUdev : public DeviceManagerEvdev,

[rjkroege, 2014/02/03 15:36:55]

this class looks sufficiently rich as to require unit tests...  You can add them
in a different CL if you want. But I think they're a really good idea.

[spang, 2014/02/03 16:43:32]

I will add a TODO for now and figure out how best to test this.

+                          base::MessagePumpLibevent::Watcher {
+ public:
+  DeviceManagerUdev() {}
+  virtual ~DeviceManagerUdev() {}
+
+  // Enumerate existing devices & start watching for device changes.
+  virtual void ScanAndStartMonitoring(const EvdevDeviceCallback& device_added,
+                                      const EvdevDeviceCallback& device_removed)
+      OVERRIDE {
+    udev_ = UdevCreate();
+    if (!udev_) {
+      LOG(ERROR) << "failed to initialize libudev";
+      return;
+    }
+
+    if (!StartMonitoring(device_added, device_removed))
+      LOG(ERROR) << "failed to start monitoring device changes via udev";
+
+    if (!UdevEnumerateInputDevices(udev_.get(), device_added))
+      LOG(ERROR) << "failed to enumerate input devices via udev";
+  }
+
+  virtual void OnFileCanReadWithoutBlocking(int fd) OVERRIDE {
+    // The netlink socket should never become disconnected. There's no need
+    // to handle broken connections here.
+
+    scoped_udev_device device(udev_monitor_receive_device(udev_monitor_.get()));
+    if (!device)
+      return;
+
+    const char* path = udev_device_get_devnode(device.get());
+    const char* action = udev_device_get_action(device.get());
+    if (!path || !action)
+      return;
+
+    if (!strcmp(action, "add") || !strcmp(action, "change"))
+      device_added_.Run(base::FilePath(path));
+    else if (!strcmp(action, "remove"))
+      device_removed_.Run(base::FilePath(path));
+  }
+
+  virtual void OnFileCanWriteWithoutBlocking(int fd) OVERRIDE { NOTREACHED(); }
+
+ private:
+  bool StartMonitoring(const EvdevDeviceCallback& device_added,
+                       const EvdevDeviceCallback& device_removed) {
+    udev_monitor_ = UdevCreateMonitor(udev_.get());
+    if (!udev_monitor_)
+      return false;
+
+    // Grab monitor socket.
+    int fd = udev_monitor_get_fd(udev_monitor_.get());
+    if (fd < 0)
+      return false;
+
+    // Save callbacks.
+    device_added_ = device_added;
+    device_removed_ = device_removed;
+
+    // Watch for incoming events on monitor socket.
+    return base::MessagePumpOzone::Current()->WatchFileDescriptor(

[rjkroege, 2014/02/03 15:36:55]

this is on the UI thread. I think putting it on an I/O thread would be
preferable? Or can you convince me that udev is sufficiently bounded in latency
in permit execution on ui?

[spang, 2014/02/03 16:43:32]

TODO.

+        fd, true, base::MessagePumpLibevent::WATCH_READ, &controller_, this);
+  }
+
+  // Udev daemon connection.
+  scoped_udev udev_;
+
+  // Udev device change monitor.
+  scoped_udev_monitor udev_monitor_;
+
+  // Callbacks for device changes.
+  EvdevDeviceCallback device_added_;
+  EvdevDeviceCallback device_removed_;
+
+  // Watcher for uevent netlink socket.
+  base::MessagePumpLibevent::FileDescriptorWatcher controller_;
+
+  DISALLOW_COPY_AND_ASSIGN(DeviceManagerUdev);
+};
+
+}  // namespace
+
+scoped_ptr<DeviceManagerEvdev> CreateDeviceManagerUdev() {
+  return scoped_ptr<DeviceManagerEvdev>(new DeviceManagerUdev);
+}
+
+}  // namespace ui