Introduce UdevDeviceGetSysattrValue, which is the same as

UdevDeviceGetPropertyValue but for sysattrs. Use this in places where
NULL is not an appropriate return value (such as assignment to
std::string).

Review URL: https://codereview.chromium.org/1018593002

Cr-Commit-Position: refs/heads/master@{#321043}

2 files changed, 19 insertions, 2 deletions

diff --git a/device/udev_linux/udev.cc b/device/udev_linux/udev.cc
index 65686da..e2b93d2 100644
--- a/device/udev_linux/udev.cc
+++ b/device/udev_linux/udev.cc
@@ -9,6 +9,14 @@
 
 namespace device {
 
+namespace {
+
+std::string StringOrEmptyIfNull(const char* value) {
+  return value ? value : std::string();
+}
+
+}  // namespace
+
 const char* udev_device_get_action(udev_device* udev_device) {
   return UdevLoader::Get()->udev_device_get_action(udev_device);
 }
@@ -149,8 +157,12 @@ void udev_unref(udev* udev) {
 
 std::string UdevDeviceGetPropertyValue(udev_device* udev_device,
                                        const char* key) {
-  const char* value = device::udev_device_get_property_value(udev_device, key);
-  return value ? value : std::string();
+  return StringOrEmptyIfNull(udev_device_get_property_value(udev_device, key));
+}
+
+std::string UdevDeviceGetSysattrValue(udev_device* udev_device,
+                                      const char* key) {
+  return StringOrEmptyIfNull(udev_device_get_sysattr_value(udev_device, key));
 }
 
 std::string UdevDecodeString(const std::string& encoded) {
diff --git a/device/udev_linux/udev.h b/device/udev_linux/udev.h
index d62db6b..c40603d 100644
--- a/device/udev_linux/udev.h
+++ b/device/udev_linux/udev.h
@@ -79,6 +79,11 @@ void udev_unref(udev* udev);
 std::string UdevDeviceGetPropertyValue(udev_device* udev_device,
                                        const char* key);
 
+// Calls udev_device_get_sysattr_value() and replaces missing values with
+// the empty string.
+std::string UdevDeviceGetSysattrValue(udev_device* udev_device,
+                                      const char* key);
+
 // Decodes udev-encoded string. Useful for decoding "*_ENC" udev properties.
 std::string UdevDecodeString(const std::string& encoded);