chromeos: Add CPU temperature reader

chromeos/system/cpu_temperature_reader.cc

Index: chromeos/system/cpu_temperature_reader.cc
diff --git a/chromeos/system/cpu_temperature_reader.cc b/chromeos/system/cpu_temperature_reader.cc
new file mode 100644
index 0000000000000000000000000000000000000000..2db816668ee7c61ef68aa69704c17f5b6586420c
--- /dev/null
+++ b/chromeos/system/cpu_temperature_reader.cc
@@ -0,0 +1,112 @@
+// Copyright 2017 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 "chromeos/system/cpu_temperature_reader.h"
+
+#include "base/files/file_enumerator.h"
+#include "base/files/file_path.h"
+#include "base/files/file_util.h"
+#include "base/location.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
+#include "base/task_scheduler/post_task.h"
+#include "base/task_scheduler/task_traits.h"
+
+namespace chromeos {
+namespace system {
+
+using CPUTemperatureInfo = CPUTemperatureReader::CPUTemperatureInfo;
+
+namespace {
+
+// The location we read our CPU temperature and channel label from.
+constexpr char kDefaultHwmonDir[] = "/sys/class/hwmon/";
+constexpr char kDeviceDir[] = "device";
+constexpr char kHwmonDirectoryPattern[] = "hwmon*";
+constexpr char kCPUTempFilePattern[] = "temp*_input";
+
+// The contents of sysfs files might contain a newline at the end. Use this
+// function to read from a sysfs file and remove the newline.
+bool ReadFileContentsAndTrimWhitespace(const base::FilePath& path,
+                                       std::string* contents_out) {
+  if (!base::ReadFileToString(path, contents_out))
+    return false;
+  base::TrimWhitespaceASCII(*contents_out, base::TRIM_TRAILING, contents_out);
+  return true;
+}
+
+bool ReadTemperatureFromPath(const base::FilePath& path,

[Daniel Erat, 2017/04/21 21:01:20]

nit: add a comment describing this method

[Simon Que, 2017/04/24 13:59:17]

Done.

+                             double* temp_celsius_out) {
+  std::string temperature_string;
+  if (!ReadFileContentsAndTrimWhitespace(path, &temperature_string))
+    return false;
+  uint32_t temperature = 0;
+  if (!base::StringToUint(temperature_string, &temperature))
+    return false;
+  *temp_celsius_out = temperature / 1000.;

[Daniel Erat, 2017/04/21 21:01:20]

nit: add '0' after '.'

[Simon Que, 2017/04/24 13:59:17]

Done.

+  return true;
+}
+
+// Get the label describing this temperature. Use the file "temp*_label" if it

[Daniel Erat, 2017/04/21 21:01:20]

nit: s/Get/Gets/

[Simon Que, 2017/04/24 13:59:16]

Done.

+// is present, or fall back on the file "name" or |label_path|.
+std::string GetLabelFromPath(const base::FilePath& label_path) {
+  std::string label;
+  if (base::PathExists(label_path) &&
+      ReadFileContentsAndTrimWhitespace(base::FilePath(label_path), &label) &&
+      !label.empty()) {
+    return label;
+  }
+
+  base::FilePath name_path = label_path.DirName().Append("name");
+  if (base::PathExists(name_path) &&
+      ReadFileContentsAndTrimWhitespace(name_path, &label) && !label.empty()) {
+    return label;
+  }
+  return label_path.MaybeAsASCII();
+}
+
+}  // namespace
+
+CPUTemperatureReader::CPUTemperatureReader() : hwmon_dir_(kDefaultHwmonDir) {}
+
+CPUTemperatureReader::~CPUTemperatureReader() {}

[Daniel Erat, 2017/04/21 21:01:20]

nit: i think we prefer "= default;" instead of "{}" now

[Simon Que, 2017/04/24 13:59:17]

Done.

+
+std::vector<CPUTemperatureInfo> CPUTemperatureReader::GetCPUTemperatures() {
+  std::vector<CPUTemperatureInfo> result;
+
+  // Get directories /sys/class/hwmon/hwmon*.
+  base::FileEnumerator hwmon_enumerator(base::FilePath(hwmon_dir_), false,
+                                        base::FileEnumerator::DIRECTORIES,
+                                        kHwmonDirectoryPattern);
+  for (base::FilePath hwmon_path = hwmon_enumerator.Next(); !hwmon_path.empty();
+       hwmon_path = hwmon_enumerator.Next()) {
+    // Get temp*_input files in hwmon*/ and hwmon*/device/.
+    if (base::PathExists(hwmon_path.Append(kDeviceDir))) {
+      hwmon_path = hwmon_path.Append(kDeviceDir);
+    }
+    base::FileEnumerator enumerator(
+        hwmon_path, false, base::FileEnumerator::FILES, kCPUTempFilePattern);
+    for (base::FilePath temperature_path = enumerator.Next();
+         !temperature_path.empty(); temperature_path = enumerator.Next()) {
+      // Get appropriate temp*_label file.
+      std::string label_path = temperature_path.MaybeAsASCII();

[Daniel Erat, 2017/04/21 21:01:20]

it feels confusing how you initialize this local here, use it in a log message,
and then later modify it. i'd recommend reading the temperature first (using
temperature_path.value() if you need to log) and then putting all the label
stuff after that.

[Simon Que, 2017/04/24 13:59:17]

Done.

+      if (label_path.empty()) {
+        LOG(WARNING) << "Unable to parse a path to temp*_input file as ASCII";
+        continue;
+      }
+      CPUTemperatureInfo info;
+      if (!ReadTemperatureFromPath(temperature_path, &info.temp_celsius)) {
+        LOG(WARNING) << "Unable to read CPU temperature from " << label_path;
+        continue;
+      }
+      base::ReplaceSubstringsAfterOffset(&label_path, 0, "input", "label");
+      info.label = GetLabelFromPath(base::FilePath(label_path));
+      result.push_back(info);
+    }
+  }
+  return result;
+}
+
+}  // namespace system
+}  // namespace chromeos