MDEV-11904 Make Audit Plugin working with MySQL 8.0.

        MySQL 8.0 basically inherits the 5.7 model, though some
        modeifications required for the plugin.

plugin/server_audit/server_audit.c

@@ -2297,10 +2297,10 @@ typedef struct loc_system_variables
 } LOC_SV;
 
 
+static int init_done= 0;
+
 static int server_audit_init(void *p __attribute__((unused)))
 {
-  const void *my_hash_init_ptr;
-
   if (!serv_ver)
   {
 #ifdef _WIN32
@@ -2309,11 +2309,16 @@ static int server_audit_init(void *p __attribute__((unused)))
     serv_ver= server_version;
 #endif /*_WIN32*/
   }
-  my_hash_init_ptr= dlsym(RTLD_DEFAULT, "_my_hash_init");
-  if (!my_hash_init_ptr)
+  if (!mysql_57_started)
   {
-    maria_above_5= 1;
-    my_hash_init_ptr= dlsym(RTLD_DEFAULT, "my_hash_init2");
+    const void *my_hash_init_ptr= dlsym(RTLD_DEFAULT, "_my_hash_init");
+    if (!my_hash_init_ptr)
+    {
+      maria_above_5= 1;
+      my_hash_init_ptr= dlsym(RTLD_DEFAULT, "my_hash_init2");
+    }
+    if (!my_hash_init_ptr)
+      return 1;
   }
 
   if(!(int_mysql_data_home= dlsym(RTLD_DEFAULT, "mysql_data_home")))
@@ -2322,7 +2327,7 @@ static int server_audit_init(void *p __attribute__((unused)))
       int_mysql_data_home= &default_home;
   }
 
-  if (!serv_ver || !my_hash_init_ptr)
+  if (!serv_ver)
     return 1;
 
   if (!started_mysql)
@@ -2402,6 +2407,7 @@ static int server_audit_init(void *p __attribute__((unused)))
   if (logging)
     start_logging();
 
+  init_done= 1;
   return 0;
 }
 
@@ -2417,6 +2423,10 @@ static int server_audit_init_mysql(void *p)
 
 static int server_audit_deinit(void *p __attribute__((unused)))
 {
+  if (!init_done)
+    return 0;
+
+  init_done= 0;
   coll_free(&incl_user_coll);
   coll_free(&excl_user_coll);
 
@@ -2839,13 +2849,15 @@ void __attribute__ ((constructor)) audit_plugin_so_init(void)
       if (sc >= 24)
         use_event_data_for_disconnect= 1;
     }
-    else if (serv_ver[0] == '5' && serv_ver[2] == '7')
+    else if ((serv_ver[0] == '5' && serv_ver[2] == '7') ||
+             (serv_ver[0] == '8' && serv_ver[2] == '0'))
     {
       mysql_57_started= 1;
       _mysql_plugin_declarations_[0].info= mysql_v4_descriptor;
       use_event_data_for_disconnect= 1;
     }
-    MYSQL_SYSVAR_NAME(loc_info).flags= PLUGIN_VAR_READONLY | PLUGIN_VAR_MEMALLOC;
+    MYSQL_SYSVAR_NAME(loc_info).flags= PLUGIN_VAR_STR | PLUGIN_VAR_THDLOCAL |
+      PLUGIN_VAR_READONLY | PLUGIN_VAR_MEMALLOC;
   }
 
   memset(locinfo_ini_value, 'O', sizeof(locinfo_ini_value)-1);