SingleLogSource handles rotation of log files

chrome/browser/chromeos/system_logs/single_log_source.h

 // 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_SYSTEM_LOGS_SINGLE_LOG_SOURCE_H_
 #define CHROME_BROWSER_CHROMEOS_SYSTEM_LOGS_SINGLE_LOG_SOURCE_H_
 
 #include <stddef.h>
+#include <sys/types.h>
 
 #include "base/files/file.h"
 #include "base/macros.h"
 #include "chrome/browser/feedback/system_logs/system_logs_fetcher.h"
 #include "components/feedback/anonymizer_tool.h"
 
 namespace system_logs {
 
 // Gathers log data from a single source, possibly incrementally.
 class SingleLogSource : public SystemLogsSource {
  public:
   enum class SupportedSource {
     // For /var/log/messages.
     kMessages,
 
     // For /var/log/ui/ui.LATEST.
     kUiLatest,
   };
 
   explicit SingleLogSource(SupportedSource source);
   ~SingleLogSource() override;
 
   // system_logs::SystemLogsSource:
   void Fetch(const SysLogsSourceCallback& callback) override;
 
  private:
   friend class SingleLogSourceTest;
 
+  // Returns the full path of the log file.
+  base::FilePath GetLogFilePath() const;
+
   // Reads all available content from |file_| that has not already been read.
-  void ReadFile(SystemLogsResponse* result);
+  // Stores results as a single entry in |result|, with |source_name()| as key
+  // and the read log contents as value.
+  //
+  // Handles rotation of underlying log file by reading all remaining contents
+  // of old file and then opening and reading from new file.
+  //
+  // |num_rotations_allowed| limits the number of rotations that can take place
+  // before the function returns. This avoids this function never returning due
+  // to indefinitely repeated log file rotation. If this number is exceeded
+  // during a call, ReadFile() stops checking for log file rotation for the
+  // remainder of its execution. Any further rotation could result in missed log
+  // data.
+  void ReadFile(size_t num_rotations_allowed, SystemLogsResponse* result);
 
   // Path to system log file directory.
   base::FilePath log_file_dir_path_;
 
   // Keeps track of how much data has been read from |file_|.
   size_t num_bytes_read_;
 
   // Handle for reading the log file that is source of logging data.
   base::File file_;
 
+  // File system inode value that was associated with |log_file_path_| when it
+  // was originally opened for reading.
+  ino_t file_inode_;
+
   // For removing PII from log results.
   feedback::AnonymizerTool anonymizer_;
 
   base::WeakPtrFactory<SingleLogSource> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SingleLogSource);
 };
 
 }  // namespace system_logs
 
 #endif  // CHROME_BROWSER_CHROMEOS_SYSTEM_LOGS_SINGLE_LOG_SOURCE_H_