Fix for BUG#3829 "Setting server_id on fly doesn't allow replication to start"

(fix by our Harrison Fisk): when one does SET GLOBAL SERVER_ID=x, we must set
server_id_supplied to 1.


sql/mysql_priv.h:
  server_id_supplied must be here to be visible in set_var.cc
sql/mysqld.cc:
  rephrasing warnings when server id is not set explicitely.
sql/set_var.cc:
  when one does SET GLOBAL SERVER_ID=x; it should be considered as explicitely setting
  the server id, so do server_id_supplied=1.
sql/slave.cc:
  Correcting wrong comment

sql/mysql_priv.h

@@ -703,7 +703,7 @@ extern uint protocol_version,dropping_tables;
 extern uint delay_key_write_options, lower_case_table_names;
 extern bool opt_endinfo, using_udf_functions, locked_in_memory;
 extern bool opt_using_transactions, mysql_embedded;
-extern bool using_update_log, opt_large_files;
+extern bool using_update_log, opt_large_files, server_id_supplied;
 extern bool opt_log, opt_update_log, opt_bin_log, opt_slow_log, opt_error_log;
 extern bool opt_disable_networking, opt_skip_show_db;
 extern bool volatile abort_loop, shutdown_in_progress, grant_option;

sql/mysqld.cc

@@ -2354,15 +2354,15 @@ You should consider changing lower_case_table_names to 1 or 2",
 #ifdef EXTRA_DEBUG
     case 1:
       sql_print_error("\
-Warning: You have enabled the binary log, but you haven't set server-id:\n\
-Updates will be logged to the binary log, but connections to slaves will\n\
-not be accepted.");
+Warning: You have enabled the binary log, but you haven't set server-id to \
+a non-zero value: we force server id to 1; updates will be logged to the \
+binary log, but connections from slaves will not be accepted.");
       break;
 #endif
     case 2:
       sql_print_error("\
-Warning: You should set server-id to a non-0 value if master_host is set.\n\
-The server will not act as a slave.");
+Warning: You should set server-id to a non-0 value if master_host is set; \
+we force server id to 2, but this MySQL server will not act as a slave.");
       break;
     }
   }

sql/set_var.cc

@@ -90,6 +90,7 @@ static void fix_max_relay_log_size(THD *thd, enum_var_type type);
 static void fix_max_connections(THD *thd, enum_var_type type);
 static void fix_thd_mem_root(THD *thd, enum_var_type type);
 static void fix_trans_mem_root(THD *thd, enum_var_type type);
+static void fix_server_id(THD *thd, enum_var_type type);
 
 /*
   Variable definition list
@@ -235,7 +236,7 @@ sys_var_thd_bool
 sys_query_cache_wlock_invalidate("query_cache_wlock_invalidate",
 				 &SV::query_cache_wlock_invalidate);
 #endif /* HAVE_QUERY_CACHE */
-sys_var_long_ptr	sys_server_id("server_id",&server_id);
+sys_var_long_ptr	sys_server_id("server_id", &server_id, fix_server_id);
 sys_var_bool_ptr	sys_slave_compressed_protocol("slave_compressed_protocol",
 						      &opt_slave_compressed_protocol);
 sys_var_long_ptr	sys_slave_net_timeout("slave_net_timeout",
@@ -811,6 +812,10 @@ static void fix_trans_mem_root(THD *thd, enum_var_type type)
                         thd->variables.trans_prealloc_size);
 }
 
+static void fix_server_id(THD *thd, enum_var_type type)
+{
+  server_id_supplied = 1;
+}
 
 bool sys_var_long_ptr::update(THD *thd, set_var *var)
 {

sql/slave.cc

@@ -143,13 +143,11 @@ int init_slave()
     goto err;
   }
 
-  /*
-    make sure slave thread gets started if server_id is set,
-    valid master.info is present, and master_host has not been specified
-  */
   if (server_id && !master_host && active_mi->host[0])
     master_host= active_mi->host;
 
+  /* If server id is not set, start_slave_thread() will say it */
+
   if (master_host && !opt_skip_slave_start)
   {
     if (start_slave_threads(1 /* need mutex */,