Enable system.log.rotate_... system configuration

In the previous versions, log rotation options were supported as
--log-rotate-age or --log-rotate-size via command line options.

On Windows, as fluentd is launched as a windows service, it is
required to configure again via --reg-winsvc-fluentdopt or edit
fluentdopt registry key for customization.

This approach is not convenient for Windows users, so it may be better
to support more comprehensive solution - customize via configuration
file.

This commit introduces such a configurable parameter in .conf

  <system>
   <log>
     rotate_age 5
     rotate_size 1048576
   </log>
  </system>

Signed-off-by: Kentaro Hayashi <hayashi@clear-code.com>

lib/fluent/supervisor.rb

@@ -600,11 +600,26 @@ def initialize(opt)
       @chgroup = opt[:chgroup]
       @chuser = opt[:chuser]
 
-      @log_rotate_age = opt[:log_rotate_age]
-      @log_rotate_size = opt[:log_rotate_size]
       @signame = opt[:signame]
 
       @cl_opt = opt
+      # parse configuration immediately to initialize logger correctly
+      @conf = Fluent::Config.build(config_path: @config_path, encoding: @conf_encoding, use_v1_config: @use_v1_config)
+      @system_config = build_system_config(@conf)
+      if @system_config.log
+        @log_rotate_age ||=  opt[:log_rotate_age]
+        if @system_config.log.rotate_age
+          if %w(daily meekly monthly).include?(@system_config.log.rotate_age)
+            @log_rotate_age = @system_config.log.rotate_age
+          else
+            @log_rotate_age = @system_config.log.rotate_age.to_i
+          end
+        end
+        @log_rotate_size = opt[:log_rotate_size] || @system_config.log.rotate_size
+      else
+        @log_rotate_age = opt[:log_rotate_age]
+        @log_rotate_size = opt[:log_rotate_size]
+      end
       @conf = nil
 
       log_opts = {suppress_repeated_stacktrace: opt[:suppress_repeated_stacktrace], ignore_repeated_log_interval: opt[:ignore_repeated_log_interval],

lib/fluent/system_config.rb

@@ -55,6 +55,8 @@ class SystemConfig
     config_section :log, required: false, init: true, multi: false do
       config_param :format, :enum, list: [:text, :json], default: :text
       config_param :time_format, :string, default: '%Y-%m-%d %H:%M:%S %z'
+      config_param :rotate_age, :string, default: nil
+      config_param :rotate_size, :integer, default: nil
     end
 
     config_section :counter_server, multi: false do