OTP-5037 Document debug support.

          Debug trace output for connection activity could be enabled
          setting the trace level as an integer to the EI_TRACELEVEL
          environment variable. This option could also be read and set from
          a running program using ei_get_tracelevel(void) and
          ei_set_tracelevel(int).

1 files changed, 21 insertions, 0 deletions

diff --git a/lib/erl_interface/doc/src/ei_connect.xml b/lib/erl_interface/doc/src/ei_connect.xml
index 08e7b122c6..abf705f9e2 100644
--- a/lib/erl_interface/doc/src/ei_connect.xml
+++ b/lib/erl_interface/doc/src/ei_connect.xml
@@ -619,6 +619,16 @@ typedef struct {
         <p>These are convenience functions for some common name lookup functions.</p>
       </desc>
     </func>
+    <func>
+      <name><ret>int</ret><nametext>ei_get_tracelevel(void)</nametext></name>
+      <name><ret>void</ret><nametext>ei_set_tracelevel(int level)</nametext></name>
+      <fsummary>Get and set functions for tracing.</fsummary>
+      <desc>
+        <p>These functions are used to set tracing on the distribution. The levels are different verbosity levels. A higher level means more information.
+	See also Debug Information and <c><![CDATA[EI_TRACELEVEL]]></c> below. </p>
+	<p> <c><![CDATA[ei_set_tracelevel]]></c> and <c><![CDATA[ei_get_tracelevel]]></c> are not thread safe.  </p>
+      </desc>
+    </func>
   </funcs>
 
   <section>
@@ -634,6 +644,17 @@ typedef struct {
       <item>the environment variable <c><![CDATA[ERL_EPMD_PORT]]></c>
        is set correctly.</item>
     </list>
+    <p>The connection attempt can be traced by setting a tracelevel by either using
+    <c><![CDATA[ei_set_tracelevel]]></c> or by setting the environment variable <c><![CDATA[EI_TRACELEVEL]]></c>.
+    The different tracelevels has the following messages:</p>
+    <list>
+    	<item>1: Verbose error messages</item>
+    	<item>2: Above messages and verbose warning messages </item>
+    	<item>3: Above messages and progress reports for connection handling</item>
+    	<item>4: Above messages and progress reports for communication</item>
+    	<item>5: Above messages and progress reports for data conversion</item>
+    </list>
   </section>
+
 </cref>