[serial] Enumerate platform serial ports

This adds code to recognize platform serial ports which aren't on a
particular bus like USB. They are identifiable because they end up in
the /devices/platform namespace.

Bug: 981483
Change-Id: I95613d57fd81a1edd060b140fd9b47f5297037b6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1760986Reviewed-by: Ovidio de Jesús Ruiz-Henríquez <odejesush@chromium.org>
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688300}

services/device/serial/serial_device_enumerator_linux.cc

@@ -12,6 +12,7 @@
 
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
 #include "base/threading/scoped_blocking_call.h"
 
 namespace device {
@@ -74,26 +75,58 @@ void SerialDeviceEnumeratorLinux::OnDeviceAdded(ScopedUdevDevicePtr device) {
   if (!subsystem || strcmp(subsystem, kSerialSubsystem) != 0)
     return;
 
+  const char* syspath_str = udev_device_get_syspath(device.get());
+  if (!syspath_str)
+    return;
+  std::string syspath(syspath_str);
+
+  // Platform serial ports.
+  if (base::StartsWith(syspath, "/sys/devices/platform/",
+                       base::CompareCase::SENSITIVE)) {
+    CreatePort(std::move(device), syspath);
+    return;
+  }
+
+  // USB serial ports and others that have a proper bus identifier.
+  const char* bus = udev_device_get_property_value(device.get(), kHostBusKey);
+  if (bus) {
+    CreatePort(std::move(device), syspath);
+    return;
+  }
+
+  // Bluetooth ports are virtual TTYs but have an identifiable major number.
+  const char* major = udev_device_get_property_value(device.get(), kMajorKey);
+  if (major && base::StringPiece(major) == kRfcommMajor) {
+    CreatePort(std::move(device), syspath);
+    return;
+  }
+}
+
+void SerialDeviceEnumeratorLinux::OnDeviceChanged(ScopedUdevDevicePtr device) {}
+
+void SerialDeviceEnumeratorLinux::OnDeviceRemoved(ScopedUdevDevicePtr device) {
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+  base::ScopedBlockingCall scoped_blocking_call(FROM_HERE,
+                                                base::BlockingType::MAY_BLOCK);
+
   const char* syspath = udev_device_get_syspath(device.get());
   if (!syspath)
     return;
 
+  auto it = paths_.find(syspath);
+  if (it == paths_.end())
+    return;
+
+  ports_.erase(it->second);
+  paths_.erase(it);
+}
+
+void SerialDeviceEnumeratorLinux::CreatePort(ScopedUdevDevicePtr device,
+                                             const std::string& syspath) {
   const char* path = udev_device_get_property_value(device.get(), kHostPathKey);
   if (!path)
     return;
 
-  // TODO(rockot): There may be a better way to filter serial devices here,
-  // but it's not clear what that would be. Udev will list lots of virtual
-  // devices with no real endpoint to back them anywhere. The presence of
-  // a bus identifier (e.g., "pci" or "usb") seems to be a good heuristic
-  // for detecting actual devices.
-  const char* bus = udev_device_get_property_value(device.get(), kHostBusKey);
-  if (!bus) {
-    const char* major = udev_device_get_property_value(device.get(), kMajorKey);
-    if (!major || strcmp(major, kRfcommMajor) != 0)
-      return;
-  }
-
   auto token = base::UnguessableToken::Create();
   auto info = mojom::SerialPortInfo::New();
   info->path = base::FilePath(path);
@@ -122,23 +155,4 @@ void SerialDeviceEnumeratorLinux::OnDeviceAdded(ScopedUdevDevicePtr device) {
   paths_.insert(std::make_pair(syspath, token));
 }
 
-void SerialDeviceEnumeratorLinux::OnDeviceChanged(ScopedUdevDevicePtr device) {}
-
-void SerialDeviceEnumeratorLinux::OnDeviceRemoved(ScopedUdevDevicePtr device) {
-  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
-  base::ScopedBlockingCall scoped_blocking_call(FROM_HERE,
-                                                base::BlockingType::MAY_BLOCK);
-
-  const char* syspath = udev_device_get_syspath(device.get());
-  if (!syspath)
-    return;
-
-  auto it = paths_.find(syspath);
-  if (it == paths_.end())
-    return;
-
-  ports_.erase(it->second);
-  paths_.erase(it);
-}
-
 }  // namespace device

services/device/serial/serial_device_enumerator_linux.h

@@ -36,6 +36,8 @@ class SerialDeviceEnumeratorLinux : public SerialDeviceEnumerator,
   void OnDeviceRemoved(ScopedUdevDevicePtr device) override;
 
  private:
+  void CreatePort(ScopedUdevDevicePtr device, const std::string& syspath);
+
   std::unique_ptr<UdevWatcher> watcher_;
   std::map<base::UnguessableToken, mojom::SerialPortInfoPtr> ports_;
   std::map<std::string, base::UnguessableToken> paths_;