logger: Rework configuration of logger

Most logger configuration that was possible through
kernel application variables have been moved into a
common 'logger' application environment in kernel.

Now all the configuration possible through the logger
API can be done as sys config.

The handler started by kernel has been renamed to 'default'
instead of logger_std_h.

There is a new logger:setup_handlers/1 function that given an
application name can be used to setup handlers in other applications.

1 files changed, 97 insertions, 4 deletions

diff --git a/lib/kernel/doc/src/logger_chapter.xml b/lib/kernel/doc/src/logger_chapter.xml
index 3150c5adb4..484358f392 100644
--- a/lib/kernel/doc/src/logger_chapter.xml
+++ b/lib/kernel/doc/src/logger_chapter.xml
@@ -248,11 +248,97 @@
   <section>
     <title>Configuration</title>
 
+    <p>Logger can be configured either when the system starts through
+      <seealso marker="config">configuration parameters</seealso>,
+      or at run-time by using the <seealso marker="logger">logger</seealso>
+      API. The recommended approach is to do the initial configuration in
+      the <c>sys.config</c> file and then use the API when some configuration
+      has to be changed at run-time, such as the logging level.</p>
+
     <section>
-      <title>Application environment variables</title>
-      <p>See <seealso marker="kernel_app#configuration">Kernel(6)</seealso> for
-	information about the application environment variables that can
-	be used for configuring logger.</p>
+      <title>Application configuration parameters</title>
+      <p>Logger is best configured by using the configuration parameters
+      of kernel. There are three possible configuration parameters:
+      <seealso marker="#logger"><c>logger</c></seealso>,
+      <seealso marker="kernel_app#logger_level"><c>logger_level</c></seealso>,
+      <seealso marker="kernel_app#logger_sasl_compatible"><c>logger_sasl_compatible</c></seealso> and
+      <seealso marker="kernel_app#logger_log_progress"><c>logger_log_progress</c></seealso>.
+      logger_level, logger_sasl_compatible and logger_log_progress are described in the
+      <seealso marker="kernel_app#configuration">Kernel Configuration</seealso>,
+      while <c>logger</c> is described below.</p>
+      <section>
+        <marker id="logger"/>
+        <title>logger</title>
+        <p>The <c>logger</c> application configuration parameter is used to configure
+          three different logger aspects; handlers, logger filters and module levels.
+          The configuration is a list containing tagged tuples that look like this:</p>
+        <taglist>
+          <tag><c>DisableHandler = {handler,default,undefined}</c></tag>
+          <item>Disable the default handler. This will allow another application
+            to add its own default handler. See <seealso marker="logger#add_handlers/1">
+            <c>logger:add_handlers/1</c></seealso> for more details.</item>
+          <tag><c>AddHandler = {handler,HandlerId,Module,HandlerConfig}</c></tag>
+          <item>Add a handler as if <seealso marker="logger:add_handler/3">
+            <c>logger:add_handler(HandlerId,Module,HandlerConfig)</c></seealso> had been
+            called.</item>
+          <tag><c>Filters = {filters, FilterDefault, [Filter]}</c><br/>
+          <c>FilterDefault = log | stop</c><br/>
+          <c>Filter = {FilterId, {FilterFun, FilterConfig}}</c></tag>
+          <item>Add the specified <seealso marker="logger#add_logger_filter/2">
+          logger filters</seealso>. Only one entry is allowed of this option.</item>
+          <tag><c>ModuleLevel</c></tag>
+          <item><c>{module_level, Level, [Module]}</c>,
+            this option configures the <seealso marker="logger#set_module_level/2">
+            module log level</seealso> to be used. It is possible to have multiple
+            <c>module_level</c> entries.</item>
+        </taglist>
+        <p>Examples:</p>
+        <list>
+          <item>
+          <p>Output logs into a the file &quot;logs/erlang.log&quot;</p>
+            <code>
+[{kernel,
+  [{logger,
+    [{handler, default, logger_std_h,
+      #{ logger_std_h => #{ type => {file,"log/erlang.log"}}}}]}]}].
+            </code>
+          </item>
+          <item>
+          <p>Output logs in single line format</p>
+            <code>
+[{kernel,
+  [{logger,
+    [{handler, default, logger_std_h,
+      #{ formatter => { logger_formatter,#{ single_line => true}}}}]}]}].
+            </code>
+          </item>
+          <item>
+          <p>Add the pid to each log event</p>
+            <code>
+[{kernel,
+  [{logger,
+    [{handler, default, logger_std_h,
+      #{ formatter => { logger_formatter,
+                        #{ template => [time," ",pid," ",msg,"\n"]}}
+       }}]}]}].
+            </code>
+          </item>
+          <item>
+          <p>Use a different file for debug logging</p>
+            <code>
+[{kernel,
+  [{logger,
+    [{handler, default, logger_std_h,
+      #{ level => error,
+         logger_std_h => #{ type => {file, "log/erlang.log"}}}},
+     {handler, info, logger_std_h,
+      #{ level => debug,
+         logger_std_h => #{ type => {file, "log/debug.log"}}}}
+     ]}]}].
+            </code>
+          </item>
+        </list>
+      </section>
     </section>
 
     <section>
@@ -330,6 +416,13 @@
 	      <c>logger_formatter</c></seealso>, and <c>Extra</c> is
 	      it's configuration map.</p>
 	</item>
+        <tag>HandlerConfig, <c>term() = term()</c></tag>
+        <item>
+          Any keys not listed above are considered to be handler specific
+          configuration. The configuration of the Kernel handlers can be found in
+          <seealso marker="logger_std_h"><c>logger_std_h</c></seealso> and
+          <seealso marker="logger_disk_log_h"><c>logger_disk_log_h</c></seealso>.
+        </item>
       </taglist>
 
       <p>Note that <c>level</c> and <c>filters</c> are obeyed by