2 bugfixes:

- Bug #985: "Between RESET SLAVE and START SLAVE, SHOW SLAVE STATUS is wrong."
Now RESET SLAVE puts correct info in mi->host etc. A new test rpl_reset_slave
for that.
- Bug #986: "CHANGE MASTER & START SLAVE do not reset error columns in SHOW
SLAVE STATUS". Now these reset the errors.


mysql-test/r/rpl_loaddata.result:
  result update.
mysql-test/t/rpl_loaddata.test:
  Test that RESET SLAVE, START SLAVE and CHANGE MASTER all reset 
  Last_slave_error and Last_slave_errno (columns of SHOW SLAVE STATUS).
  We do it in this test because that's one of tests which have 
  an intentional query error on the slave.
sql/slave.cc:
  As we need TWICE the code to copy command-line options (--master-host etc)
  to mi (we already had it in init_master_info, but we also need it in RESET
  SLAVE to fix bug#985), I make a function of this code.
  And a function to reset Last_slave_error and Last_slave_errno (we need
  it in CHANGE MASTER, RESET SLAVE, and at the start of the SQL thread).
sql/slave.h:
  declarations for new functions.
sql/sql_repl.cc:
  copy --master-host etc to mi in RESET SLAVE, so that SHOW SLAVE STATUS
  shows correct information.

mysql-test/r/rpl_loaddata.result

@@ -25,3 +25,29 @@ drop table t3;
 create table t1(a int, b int, unique(b));
 insert into t1 values(1,10);
 load data infile '../../std_data/rpl_loaddata.dat' into table t1;
+set global sql_slave_skip_counter=1;
+start slave;
+show slave status;
+Master_Host	Master_User	Master_Port	Connect_retry	Master_Log_File	Read_Master_Log_Pos	Relay_Log_File	Relay_Log_Pos	Relay_Master_Log_File	Slave_IO_Running	Slave_SQL_Running	Replicate_do_db	Replicate_ignore_db	Last_errno	Last_error	Skip_counter	Exec_master_log_pos	Relay_log_space
+127.0.0.1	root	MASTER_PORT	1	master-bin.001	1311	slave-relay-bin.002	1352	master-bin.001	Yes	Yes			0		0	1311	1352
+set sql_log_bin=0;
+delete from t1;
+set sql_log_bin=1;
+load data infile '../../std_data/rpl_loaddata.dat' into table t1;
+stop slave;
+change master to master_user='test';
+change master to master_user='root';
+show slave status;
+Master_Host	Master_User	Master_Port	Connect_retry	Master_Log_File	Read_Master_Log_Pos	Relay_Log_File	Relay_Log_Pos	Relay_Master_Log_File	Slave_IO_Running	Slave_SQL_Running	Replicate_do_db	Replicate_ignore_db	Last_errno	Last_error	Skip_counter	Exec_master_log_pos	Relay_log_space
+127.0.0.1	root	MASTER_PORT	1	master-bin.001	1442	slave-relay-bin.001	4	master-bin.001	No	No			0		0	1442	4
+set global sql_slave_skip_counter=1;
+start slave;
+set sql_log_bin=0;
+delete from t1;
+set sql_log_bin=1;
+load data infile '../../std_data/rpl_loaddata.dat' into table t1;
+stop slave;
+reset slave;
+show slave status;
+Master_Host	Master_User	Master_Port	Connect_retry	Master_Log_File	Read_Master_Log_Pos	Relay_Log_File	Relay_Log_Pos	Relay_Master_Log_File	Slave_IO_Running	Slave_SQL_Running	Replicate_do_db	Replicate_ignore_db	Last_errno	Last_error	Skip_counter	Exec_master_log_pos	Relay_log_space
+127.0.0.1	root	MASTER_PORT	1		4	slave-relay-bin.001	4		No	No			0		0	0	4

mysql-test/r/rpl_reset_slave.result

+slave stop;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+reset master;
+reset slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+slave start;
+show slave status;
+Master_Host	Master_User	Master_Port	Connect_retry	Master_Log_File	Read_Master_Log_Pos	Relay_Log_File	Relay_Log_Pos	Relay_Master_Log_File	Slave_IO_Running	Slave_SQL_Running	Replicate_do_db	Replicate_ignore_db	Last_errno	Last_error	Skip_counter	Exec_master_log_pos	Relay_log_space
+127.0.0.1	root	MASTER_PORT	1	master-bin.001	79	slave-relay-bin.002	120	master-bin.001	Yes	Yes			0		0	79	120
+stop slave;
+change master to master_user='test';
+show slave status;
+Master_Host	Master_User	Master_Port	Connect_retry	Master_Log_File	Read_Master_Log_Pos	Relay_Log_File	Relay_Log_Pos	Relay_Master_Log_File	Slave_IO_Running	Slave_SQL_Running	Replicate_do_db	Replicate_ignore_db	Last_errno	Last_error	Skip_counter	Exec_master_log_pos	Relay_log_space
+127.0.0.1	test	MASTER_PORT	1	master-bin.001	79	slave-relay-bin.001	4	master-bin.001	No	No			0		0	79	4
+reset slave;
+show slave status;
+Master_Host	Master_User	Master_Port	Connect_retry	Master_Log_File	Read_Master_Log_Pos	Relay_Log_File	Relay_Log_Pos	Relay_Master_Log_File	Slave_IO_Running	Slave_SQL_Running	Replicate_do_db	Replicate_ignore_db	Last_errno	Last_error	Skip_counter	Exec_master_log_pos	Relay_log_space
+127.0.0.1	root	MASTER_PORT	1		4	slave-relay-bin.001	4		No	No			0		0	0	4
+start slave;
+show slave status;
+Master_Host	Master_User	Master_Port	Connect_retry	Master_Log_File	Read_Master_Log_Pos	Relay_Log_File	Relay_Log_Pos	Relay_Master_Log_File	Slave_IO_Running	Slave_SQL_Running	Replicate_do_db	Replicate_ignore_db	Last_errno	Last_error	Skip_counter	Exec_master_log_pos	Relay_log_space
+127.0.0.1	root	MASTER_PORT	1	master-bin.001	79	slave-relay-bin.002	120	master-bin.001	Yes	Yes			0		0	79	120

mysql-test/t/rpl_loaddata.test

@@ -6,6 +6,9 @@
 #
 # check if duplicate entries trigger an error (they should unless IGNORE or
 # REPLACE was used on the master) (bug 571).
+#
+# check if START SLAVE, RESET SLAVE, CHANGE MASTER reset Last_slave_error and
+# Last_slave_errno in SHOW SLAVE STATUS (1st and 3rd commands did not: bug 986).
 
 source include/master-slave.inc;
 
@@ -44,3 +47,53 @@ save_master_pos;
 connection slave;
 # The SQL slave thread should be stopped now.
 wait_for_slave_to_stop;
+
+# Skip the bad event and see if error is cleared in SHOW SLAVE STATUS by START
+# SLAVE, even though we are not executing any event (as sql_slave_skip_counter
+# takes us directly to the end of the relay log).
+
+set global sql_slave_skip_counter=1;
+start slave;
+sync_with_master;
+--replace_result $MASTER_MYPORT MASTER_PORT
+show slave status;
+
+# Trigger error again to test CHANGE MASTER
+
+connection master;
+set sql_log_bin=0;
+delete from t1;
+set sql_log_bin=1;
+load data infile '../../std_data/rpl_loaddata.dat' into table t1;
+save_master_pos;
+connection slave;
+# The SQL slave thread should be stopped now.
+wait_for_slave_to_stop;
+
+# CHANGE MASTER and see if error is cleared in SHOW SLAVE STATUS.
+stop slave;
+change master to master_user='test';
+change master to master_user='root';
+--replace_result $MASTER_MYPORT MASTER_PORT
+show slave status;
+
+# Trigger error again to test RESET SLAVE
+
+set global sql_slave_skip_counter=1;
+start slave;
+sync_with_master;
+connection master;
+set sql_log_bin=0;
+delete from t1;
+set sql_log_bin=1;
+load data infile '../../std_data/rpl_loaddata.dat' into table t1;
+save_master_pos;
+connection slave;
+# The SQL slave thread should be stopped now.
+wait_for_slave_to_stop;
+
+# RESET SLAVE and see if error is cleared in SHOW SLAVE STATUS.
+stop slave;
+reset slave;
+--replace_result $MASTER_MYPORT MASTER_PORT
+show slave status;

mysql-test/t/rpl_reset_slave.test

+# See SHOW SLAVE STATUS displays well after RESET SLAVE (it should display the
+# --master-* options from mysqld, as this is what is going to be used next time
+# slave threads will be started). In bug 985, it displayed old values (of before
+# RESET SLAVE).
+
+source include/master-slave.inc;
+connection master;
+save_master_pos;
+connection slave;
+sync_with_master;
+--replace_result $MASTER_MYPORT MASTER_PORT
+show slave status;
+
+stop slave;
+change master to master_user='test';
+--replace_result $MASTER_MYPORT MASTER_PORT
+show slave status;
+
+reset slave;
+--replace_result $MASTER_MYPORT MASTER_PORT
+show slave status;
+
+start slave;
+sync_with_master;
+--replace_result $MASTER_MYPORT MASTER_PORT
+show slave status;

sql/slave.cc

@@ -1476,6 +1476,27 @@ static int count_relay_log_space(RELAY_LOG_INFO* rli)
   DBUG_RETURN(0);
 }
 
+void init_master_info_with_options(MASTER_INFO* mi)
+{
+  mi->master_log_name[0] = 0;
+  mi->master_log_pos = BIN_LOG_HEADER_SIZE;		// skip magic number
+  
+  if (master_host)
+    strmake(mi->host, master_host, sizeof(mi->host) - 1);
+  if (master_user)
+    strmake(mi->user, master_user, sizeof(mi->user) - 1);
+  if (master_password)
+    strmake(mi->password, master_password, HASH_PASSWORD_LENGTH);
+  mi->port = master_port;
+  mi->connect_retry = master_connect_retry;
+}
+
+void clear_last_slave_error(RELAY_LOG_INFO* rli)
+{
+  //Clear the errors displayed by SHOW SLAVE STATUS
+  rli->last_slave_error[0]=0;
+  rli->last_slave_errno=0;
+}
 
 int init_master_info(MASTER_INFO* mi, const char* master_info_fname,
 		     const char* slave_info_fname,
@@ -1529,18 +1550,9 @@ file '%s')", fname);
       goto err;
     }
 
-    mi->master_log_name[0] = 0;
-    mi->master_log_pos = BIN_LOG_HEADER_SIZE;		// skip magic number
     mi->fd = fd;
-      
-    if (master_host)
-      strmake(mi->host, master_host, sizeof(mi->host) - 1);
-    if (master_user)
-      strmake(mi->user, master_user, sizeof(mi->user) - 1);
-    if (master_password)
-      strmake(mi->password, master_password, HASH_PASSWORD_LENGTH);
-    mi->port = master_port;
-    mi->connect_retry = master_connect_retry;
+    init_master_info_with_options(mi);
+
   }
   else // file exists
   {
@@ -2611,6 +2623,12 @@ slave_begin:
   pthread_cond_broadcast(&rli->start_cond);
   // This should always be set to 0 when the slave thread is started
   rli->pending = 0;
+  /*
+    Reset errors for a clean start (otherwise, if the master is idle, the SQL
+    thread may execute no Query_log_event, so the error will remain even
+    though there's no problem anymore).
+  */
+  clear_last_slave_error(rli);
 
   //tell the I/O thread to take relay_log_space_limit into account from now on
   pthread_mutex_lock(&rli->log_space_lock);

sql/slave.h

@@ -389,6 +389,8 @@ void skip_load_data_infile(NET* net);
 void slave_print_error(RELAY_LOG_INFO* rli, int err_code, const char* msg, ...);
 
 void end_slave(); /* clean up */
+void init_master_info_with_options(MASTER_INFO* mi);
+void clear_last_slave_error(RELAY_LOG_INFO* rli);
 int init_master_info(MASTER_INFO* mi, const char* master_info_fname,
 		     const char* slave_info_fname,
 		     bool abort_if_no_master_info_file);

sql/sql_repl.cc

@@ -769,12 +769,15 @@ int reset_slave(THD *thd, MASTER_INFO* mi)
 			       &errmsg)))
     goto err;
   
-  //Clear master's log coordinates (only for good display of SHOW SLAVE STATUS)
-  mi->master_log_name[0]= 0;
-  mi->master_log_pos= BIN_LOG_HEADER_SIZE;
-  //Clear the errors displayed by SHOW SLAVE STATUS
-  mi->rli.last_slave_error[0]=0;
-  mi->rli.last_slave_errno=0;
+  /*
+    Clear master's log coordinates and reset host/user/etc to the values
+    specified in mysqld's options (only for good display of SHOW SLAVE STATUS;
+    next init_master_info() (in start_slave() for example) would have set them
+    the same way; but here this is for the case where the user does SHOW SLAVE
+    STATUS; before doing START SLAVE;
+  */
+  init_master_info_with_options(mi);
+  clear_last_slave_error(&mi->rli);
   //close master_info_file, relay_log_info_file, set mi->inited=rli->inited=0
   end_master_info(mi);
   //and delete these two files
@@ -965,6 +968,8 @@ int change_master(THD* thd, MASTER_INFO* mi)
 
   pthread_mutex_lock(&mi->rli.data_lock);
   mi->rli.abort_pos_wait++; /* for MASTER_POS_WAIT() to abort */
+  /* Clear the error, for a clean start. */
+  clear_last_slave_error(&mi->rli);
   /* 
      If we don't write new coordinates to disk now, then old will remain in
      relay-log.info until START SLAVE is issued; but if mysqld is shutdown