evdev: Add hotplugging support

This adds hotplugging support to the evdev input backend. We use
libudev to monitor changes to input devices in a separate thread.
Removed devices are removed from the devices list, and new devices
are added to the list.

The effect is that controllers are usable immediately after plugging
them without having to manually refresh devices (if they were
configured to be used, of course).

Source/Core/InputCommon/ControllerInterface/ControllerInterface.cpp

@@ -106,17 +106,6 @@ void ControllerInterface::Shutdown()
   if (!m_is_init)
     return;
 
-  std::lock_guard<std::mutex> lk(m_devices_mutex);
-
-  for (const auto& d : m_devices)
-  {
-    // Set outputs to ZERO before destroying device
-    for (ciface::Core::Device::Output* o : d->Outputs())
-      o->SetState(0);
-  }
-
-  m_devices.clear();
-
 #ifdef CIFACE_USE_XINPUT
   ciface::XInput::DeInit();
 #endif
@@ -136,6 +125,20 @@ void ControllerInterface::Shutdown()
 #ifdef CIFACE_USE_ANDROID
 // nothing needed
 #endif
+#ifdef CIFACE_USE_EVDEV
+  ciface::evdev::Shutdown();
+#endif
+
+  std::lock_guard<std::mutex> lk(m_devices_mutex);
+
+  for (const auto& d : m_devices)
+  {
+    // Set outputs to ZERO before destroying device
+    for (ciface::Core::Device::Output* o : d->Outputs())
+      o->SetState(0);
+  }
+
+  m_devices.clear();
 
   m_is_init = false;
 }

Source/Core/InputCommon/ControllerInterface/evdev/evdev.cpp

@@ -5,12 +5,17 @@
 #include <fcntl.h>
 #include <libudev.h>
 #include <map>
+#include <memory>
 #include <unistd.h>
 
+#include <sys/eventfd.h>
+
 #include "Common/Assert.h"
+#include "Common/Flag.h"
 #include "Common/Logging/Log.h"
 #include "Common/MathUtil.h"
 #include "Common/StringUtil.h"
+#include "Common/Thread.h"
 #include "InputCommon/ControllerInterface/ControllerInterface.h"
 #include "InputCommon/ControllerInterface/evdev/evdev.h"
 
@@ -18,6 +23,15 @@ namespace ciface
 {
 namespace evdev
 {
+static std::thread s_hotplug_thread;
+static Common::Flag s_hotplug_thread_running;
+static int s_wakeup_eventfd;
+
+// There is no easy way to get the device name from only a dev node
+// during a device removed event, since libevdev can't work on removed devices;
+// sysfs is not stable, so this is probably the easiest way to get a name for a node.
+static std::map<std::string, std::string> s_devnode_name_map;
+
 static std::string GetName(const std::string& devnode)
 {
   int fd = open(devnode.c_str(), O_RDWR | O_NONBLOCK);
@@ -28,20 +42,110 @@ static std::string GetName(const std::string& devnode)
     close(fd);
     return std::string();
   }
-  std::string res = libevdev_get_name(dev);
+  std::string res = StripSpaces(libevdev_get_name(dev));
   libevdev_free(dev);
   close(fd);
   return res;
 }
 
+static void HotplugThreadFunc()
+{
+  Common::SetCurrentThreadName("evdev Hotplug Thread");
+  NOTICE_LOG(SERIALINTERFACE, "evdev hotplug thread started");
+
+  udev* udev = udev_new();
+  _assert_msg_(PAD, udev != nullptr, "Couldn't initialize libudev.");
+
+  // Set up monitoring
+  udev_monitor* monitor = udev_monitor_new_from_netlink(udev, "udev");
+  udev_monitor_filter_add_match_subsystem_devtype(monitor, "input", nullptr);
+  udev_monitor_enable_receiving(monitor);
+  const int monitor_fd = udev_monitor_get_fd(monitor);
+
+  while (s_hotplug_thread_running.IsSet())
+  {
+    fd_set fds;
+
+    FD_ZERO(&fds);
+    FD_SET(monitor_fd, &fds);
+    FD_SET(s_wakeup_eventfd, &fds);
+
+    int ret = select(monitor_fd + 1, &fds, nullptr, nullptr, nullptr);
+    if (ret < 1 || !FD_ISSET(monitor_fd, &fds))
+      continue;
+
+    udev_device* dev = udev_monitor_receive_device(monitor);
+
+    const char* action = udev_device_get_action(dev);
+    const char* devnode = udev_device_get_devnode(dev);
+    if (!devnode)
+      continue;
+
+    if (strcmp(action, "remove") == 0)
+    {
+      const auto it = s_devnode_name_map.find(devnode);
+      if (it == s_devnode_name_map.end())
+        continue;  // we don't know the name for this device, so it is probably not an evdev device
+      const std::string& name = it->second;
+      g_controller_interface.RemoveDevice([&name](const auto& device) {
+        return device->GetSource() == "evdev" && device->GetName() == name && !device->IsValid();
+      });
+      NOTICE_LOG(SERIALINTERFACE, "Removed device: %s", name.c_str());
+      s_devnode_name_map.erase(devnode);
+      g_controller_interface.InvokeHotplugCallbacks();
+    }
+    // Only react to "device added" events for evdev devices that we can access.
+    else if (strcmp(action, "add") == 0 && access(devnode, W_OK) == 0)
+    {
+      const std::string name = GetName(devnode);
+      if (name.empty())
+        continue;  // probably not an evdev device
+      auto device = std::make_shared<evdevDevice>(devnode);
+      if (device->IsInteresting())
+      {
+        g_controller_interface.AddDevice(std::move(device));
+        s_devnode_name_map.insert(std::pair<std::string, std::string>(devnode, name));
+        NOTICE_LOG(SERIALINTERFACE, "Added new device: %s", name.c_str());
+        g_controller_interface.InvokeHotplugCallbacks();
+      }
+    }
+    udev_device_unref(dev);
+  }
+  NOTICE_LOG(SERIALINTERFACE, "evdev hotplug thread stopped");
+}
+
+static void StartHotplugThread()
+{
+  if (s_hotplug_thread_running.IsSet())
+    return;
+
+  s_wakeup_eventfd = eventfd(0, 0);
+  _assert_msg_(PAD, s_wakeup_eventfd != -1, "Couldn't create eventfd.");
+  s_hotplug_thread_running.Set(true);
+  s_hotplug_thread = std::thread(HotplugThreadFunc);
+}
+
+static void StopHotplugThread()
+{
+  if (s_hotplug_thread_running.TestAndClear())
+  {
+    // Write something to efd so that select() stops blocking.
+    uint64_t value = 1;
+    write(s_wakeup_eventfd, &value, sizeof(uint64_t));
+    s_hotplug_thread.join();
+  }
+}
+
 void Init()
 {
-  // We use Udev to find any devices. In the future this will allow for hotplugging.
+  s_devnode_name_map.clear();
-  // But for now it is essentially iterating over /dev/input/event0 to event31. However if the
-  // naming scheme is ever updated in the future, this *should* be forwards compatable.
 
-  struct udev* udev = udev_new();
+  // During initialization we use udev to iterate over all /dev/input/event* devices.
-  _assert_msg_(PAD, udev != 0, "Couldn't initilize libudev.");
+  // Note: the Linux kernel is currently limited to just 32 event devices. If this ever
+  //            changes, hopefully udev will take care of this.
+
+  udev* udev = udev_new();
+  _assert_msg_(PAD, udev != nullptr, "Couldn't initialize libudev.");
 
   // List all input devices
   udev_enumerate* enumerate = udev_enumerate_new(udev);
@@ -69,12 +173,20 @@ void Init()
       if (input->IsInteresting())
       {
         g_controller_interface.AddDevice(std::move(input));
+        s_devnode_name_map.insert(std::pair<std::string, std::string>(devnode, name));
       }
     }
     udev_device_unref(dev);
   }
   udev_enumerate_unref(enumerate);
   udev_unref(udev);
+
+  StartHotplugThread();
+}
+
+void Shutdown()
+{
+  StopHotplugThread();
 }
 
 evdevDevice::evdevDevice(const std::string& devnode) : m_devfile(devnode)
@@ -152,6 +264,22 @@ void evdevDevice::UpdateInput()
   } while (rc >= 0);
 }
 
+bool evdevDevice::IsValid() const
+{
+  int current_fd = libevdev_get_fd(m_dev);
+  if (current_fd == -1)
+    return false;
+
+  libevdev* device;
+  if (libevdev_new_from_fd(current_fd, &device) != 0)
+  {
+    close(current_fd);
+    return false;
+  }
+  libevdev_free(device);
+  return true;
+}
+
 std::string evdevDevice::Button::GetName() const
 {
   // Buttons below 0x100 are mostly keyboard keys, and the names make sense

Source/Core/InputCommon/ControllerInterface/evdev/evdev.h

@@ -8,11 +8,14 @@
 #include <string>
 #include <vector>
 
+#include "InputCommon/ControllerInterface/ControllerInterface.h"
+
 namespace ciface
 {
 namespace evdev
 {
 void Init();
+void Shutdown();
 
 class evdevDevice : public Core::Device
 {
@@ -62,6 +65,7 @@ private:
 
 public:
   void UpdateInput() override;
+  bool IsValid() const override;
 
   evdevDevice(const std::string& devnode);
   ~evdevDevice();