Use UdevWatcher to filter USB, HID and serial devices

UsbServiceLinux, HidServiceLinux and SerialDeviceEnumeratorLinux each
only care about devices from a particular subsystem. This change avoids
processing other devices which should decrease the time it takes to
perform the initial enumeration.

Change-Id: I3535b5e6ecbb8c013957197cff151011a19a6097
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2227094
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Matt Reynolds <mattreynolds@chromium.org>
Reviewed-by: Matt Reynolds <mattreynolds@chromium.org>
Auto-Submit: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774416}

services/device/hid/hid_service_linux.cc

@@ -205,7 +205,8 @@ class HidServiceLinux::BlockingTaskRunnerHelper : public UdevWatcher::Observer {
   void Start() {
     DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 
-    watcher_ = UdevWatcher::StartWatching(this);
+    watcher_ = UdevWatcher::StartWatching(
+        this, {UdevWatcher::Filter(kSubsystemHidraw, "")});
     watcher_->EnumerateExistingDevices();
     task_runner_->PostTask(
         FROM_HERE,
@@ -224,9 +225,11 @@ class HidServiceLinux::BlockingTaskRunnerHelper : public UdevWatcher::Observer {
       return;
     HidPlatformDeviceId platform_device_id = device_path;
 
+#if DCHECK_IS_ON()
     const char* subsystem = udev_device_get_subsystem(device.get());
-    if (!subsystem || strcmp(subsystem, kSubsystemHidraw) != 0)
-      return;
+    DCHECK(subsystem);
+    DCHECK_EQ(base::StringPiece(subsystem), kSubsystemHidraw);
+#endif
 
     const char* str_property = udev_device_get_devnode(device.get());
     if (!str_property)

services/device/serial/serial_device_enumerator_linux.cc

@@ -22,6 +22,8 @@ namespace device {
 
 namespace {
 
+constexpr char kSubsystemTty[] = "tty";
+
 // Holds information about a TTY driver for serial devices. Each driver creates
 // device nodes with a given major number and in a range of minor numbers.
 struct SerialDriverInfo {
@@ -84,7 +86,8 @@ std::vector<SerialDriverInfo> ReadSerialDriverInfo() {
 SerialDeviceEnumeratorLinux::SerialDeviceEnumeratorLinux() {
   DETACH_FROM_SEQUENCE(sequence_checker_);
 
-  watcher_ = UdevWatcher::StartWatching(this);
+  watcher_ = UdevWatcher::StartWatching(
+      this, {UdevWatcher::Filter(kSubsystemTty, "")});
   watcher_->EnumerateExistingDevices();
 }
 
@@ -97,9 +100,11 @@ void SerialDeviceEnumeratorLinux::OnDeviceAdded(ScopedUdevDevicePtr device) {
   base::ScopedBlockingCall scoped_blocking_call(FROM_HERE,
                                                 base::BlockingType::MAY_BLOCK);
 
+#if DCHECK_IS_ON()
   const char* subsystem = udev_device_get_subsystem(device.get());
-  if (!subsystem || strcmp(subsystem, "tty") != 0)
-    return;
+  DCHECK(subsystem);
+  DCHECK_EQ(base::StringPiece(subsystem), kSubsystemTty);
+#endif
 
   const char* syspath_str = udev_device_get_syspath(device.get());
   if (!syspath_str)

services/device/usb/usb_service_linux.cc

@@ -34,6 +34,8 @@ namespace device {
 
 namespace {
 
+constexpr char kSubsystemUsb[] = "usb";
+
 // Standard USB requests and descriptor types:
 const uint16_t kUsbVersion2_1 = 0x0210;
 
@@ -109,7 +111,8 @@ void UsbServiceLinux::BlockingTaskRunnerHelper::Start() {
 
   // Initializing udev for device enumeration and monitoring may fail. In that
   // case this service will continue to exist but no devices will be found.
-  watcher_ = UdevWatcher::StartWatching(this);
+  watcher_ = UdevWatcher::StartWatching(
+      this, {UdevWatcher::Filter(kSubsystemUsb, "")});
   if (watcher_)
     watcher_->EnumerateExistingDevices();
 
@@ -123,9 +126,12 @@ void UsbServiceLinux::BlockingTaskRunnerHelper::OnDeviceAdded(
 
   base::ScopedBlockingCall scoped_blocking_call(FROM_HERE,
                                                 base::BlockingType::MAY_BLOCK);
+
+#if DCHECK_IS_ON()
   const char* subsystem = udev_device_get_subsystem(device.get());
-  if (!subsystem || strcmp(subsystem, "usb") != 0)
-    return;
+  DCHECK(subsystem);
+  DCHECK_EQ(base::StringPiece(subsystem), kSubsystemUsb);
+#endif
 
   const char* value = udev_device_get_devnode(device.get());
   if (!value)