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

components/metrics/serialization/serialization_utils.cc

 // Copyright 2014 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 "components/metrics/serialization/serialization_utils.h"
 
 #include <sys/file.h>
 
 #include <string>
 #include <vector>
@@ skipping 104 matching lines @@
 
 void SerializationUtils::ReadAndTruncateMetricsFromFile(
     const std::string& filename,
     ScopedVector<MetricSample>* metrics) {
   struct stat stat_buf;
   int result;
 
   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;
   }
   if (stat_buf.st_size == 0) {
     // Also nothing to collect.
     return;
   }
   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;
   }
 
   // This processes all messages in the log. When all messages are
   // read and processed, or an error occurs, truncate the file to zero size.
   for (;;) {
     std::string message;
 
     if (!ReadMessage(fd.get(), &message))
       break;
 
     scoped_ptr<MetricSample> sample = ParseSample(message);
     if (sample)
       metrics->push_back(sample.release());
   }
 
   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,
                                            const std::string& filename) {
   if (!sample.IsValid())
     return false;
 
   base::ScopedFD file_descriptor(open(filename.c_str(),
                                       O_WRONLY | O_APPEND | O_CREAT,
                                       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;
   }
 
   fchmod(file_descriptor.get(), READ_WRITE_ALL_FILE_FLAGS);
   // Grab a lock to avoid chrome truncating the file
   // underneath us. Keep the file locked as briefly as possible.
   // Freeing file_descriptor will close the file and and remove the lock.
   if (HANDLE_EINTR(flock(file_descriptor.get(), LOCK_EX)) < 0) {
     DLOG(ERROR) << "error locking" << filename << " : " << errno;
     return false;
   }
 
   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;
   }
 
   // The file containing the metrics samples will only be read by programs on
   // the same device so we do not check endianness.
   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;
   }
 
   return true;
 }
 
 }  // namespace metrics