Add output of error code for file operations in serialization_utils.cc.

components/metrics/serialization/serialization_utils.cc

Index: components/metrics/serialization/serialization_utils.cc
diff --git a/components/metrics/serialization/serialization_utils.cc b/components/metrics/serialization/serialization_utils.cc
index d57b51b2c08f09e3c9f87dacc146f40a11f4d8d3..c786f79a10a664e1eef36fe24852bf4dff4eb284 100644
--- a/components/metrics/serialization/serialization_utils.cc
+++ b/components/metrics/serialization/serialization_utils.cc
@@ -122,7 +122,7 @@ void SerializationUtils::ReadAndTruncateMetricsFromFile(
   result = stat(filename.c_str(), &stat_buf);
   if (result < 0) {
     if (errno != ENOENT)
-      DPLOG(ERROR) << filename << ": bad metrics file stat";
+      DPLOG(ERROR) << filename << ": bad metrics file stat" << " : " << errno;

[ostap, 2015/04/06 22:12:34]

Please, make message consistent - filename after message (as in other places),
or filename before message (as it was originally).

 
     // Nothing to collect---try later.
     return;
@@ -133,12 +133,12 @@ void SerializationUtils::ReadAndTruncateMetricsFromFile(
   }
   base::ScopedFD fd(open(filename.c_str(), O_RDWR));
   if (fd.get() < 0) {
-    DPLOG(ERROR) << filename << ": cannot open";
+    DPLOG(ERROR) << " cannot open: " << filename << " : " << errno;
     return;
   }
   result = flock(fd.get(), LOCK_EX);
   if (result < 0) {
-    DPLOG(ERROR) << filename << ": cannot lock";
+    DPLOG(ERROR) << "cannot lock: "  << filename << " : " << errno;
     return;
   }
 
@@ -157,11 +157,11 @@ void SerializationUtils::ReadAndTruncateMetricsFromFile(
 
   result = ftruncate(fd.get(), 0);
   if (result < 0)
-    DPLOG(ERROR) << "truncate metrics log";
+    DPLOG(ERROR) << "truncate metrics log: " << filename << " : " << errno;
 
   result = flock(fd.get(), LOCK_UN);
   if (result < 0)
-    DPLOG(ERROR) << "unlock metrics log";
+    DPLOG(ERROR) << "unlock metrics log: "  << filename << " : " << errno;
 }
 
 bool SerializationUtils::WriteMetricToFile(const MetricSample& sample,
@@ -174,7 +174,7 @@ bool SerializationUtils::WriteMetricToFile(const MetricSample& sample,
                                       READ_WRITE_ALL_FILE_FLAGS));
 
   if (file_descriptor.get() < 0) {
-    DLOG(ERROR) << "error openning the file";
+    DLOG(ERROR) << "error openning the file: " << filename << " : " << errno;
     return false;
   }
 
@@ -190,7 +190,7 @@ bool SerializationUtils::WriteMetricToFile(const MetricSample& sample,
   std::string msg = sample.ToString();
   int32 size = msg.length() + sizeof(int32);
   if (size > kMessageMaxLength) {
-    DLOG(ERROR) << "cannot write message: too long";
+    DLOG(ERROR) << "cannot write message: too long" << " : " << errno;
     return false;
   }
 
@@ -199,13 +199,13 @@ bool SerializationUtils::WriteMetricToFile(const MetricSample& sample,
   if (!base::WriteFileDescriptor(file_descriptor.get(),
                                  reinterpret_cast<char*>(&size),
                                  sizeof(size))) {
-    DPLOG(ERROR) << "error writing message length";
+    DPLOG(ERROR) << "error writing message length" << " : " << errno;
     return false;
   }
 
   if (!base::WriteFileDescriptor(
           file_descriptor.get(), msg.c_str(), msg.size())) {
-    DPLOG(ERROR) << "error writing message";
+    DPLOG(ERROR) << "error writing message" << " : " << errno;
     return false;
   }