Descriptive log for HID device open failure on Linux.

device/hid/hid_connection_linux.cc

 // Copyright (c) 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 "device/hid/hid_connection_linux.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <libudev.h>
 #include <linux/hidraw.h>
@@ skipping 39 matching lines @@
 
   int flags = base::File::FLAG_OPEN |
               base::File::FLAG_READ |
               base::File::FLAG_WRITE;
 
   base::File device_file(base::FilePath(dev_node), flags);
   if (!device_file.IsValid()) {
     base::File::Error file_error = device_file.error_details();
 
     if (file_error == base::File::FILE_ERROR_ACCESS_DENIED) {
+      VLOG(1) << "Access denied opening device read-write, trying read-only.";
+
       flags = base::File::FLAG_OPEN | base::File::FLAG_READ;
 
-      base::File device_file(base::FilePath(dev_node), flags);
-      if (!device_file.IsValid()) {
-        LOG(ERROR) << device_file.error_details();
-        return;
-      }
-    } else {
-      LOG(ERROR) << file_error;
-      return;
+      device_file = base::File(base::FilePath(dev_node), flags);
     }
   }
+  if (!device_file.IsValid()) {
+    LOG(ERROR) << "Failed to open '" << dev_node << "': "
+        << base::File::ErrorToString(device_file.error_details());
+    return;
+  }
+
   if (fcntl(device_file.GetPlatformFile(), F_SETFL,
             fcntl(device_file.GetPlatformFile(), F_GETFL) | O_NONBLOCK)) {
     PLOG(ERROR) << "Failed to set non-blocking flag to device file.";
     return;
   }
   device_file_ = device_file.Pass();
 
   if (!base::MessageLoopForIO::current()->WatchFileDescriptor(
       device_file_.GetPlatformFile(),
       true,
@@ skipping 118 matching lines @@
       read.callback.Run(false, report.buffer->size());
     } else {
       memcpy(read.buffer->data(), report.buffer->data(), report.buffer->size());
       pending_reports_.pop();
       read.callback.Run(true, report.buffer->size());
     }
   }
 }
 
 }  // namespace device