Port fix for 53165 to InnoDB 5.1 plugin. The change buffering options

are different in 5.1 comparing to that of 5.5, so a hand port is
necessary to avoid wrong default option to be set by a simple
branch merge.

storage/innodb_plugin/handler/ha_innodb.cc

@@ -10345,6 +10345,34 @@ innodb_old_blocks_pct_update(
 		*static_cast<const uint*>(save), TRUE);
 }
 
+/*************************************************************//**
+Find the corresponding ibuf_use_t value that indexes into
+innobase_change_buffering_values[] array for the input
+change buffering option name.
+@return	corresponding IBUF_USE_* value for the input variable
+name, or IBUF_USE_COUNT if not able to find a match */
+static
+ibuf_use_t
+innodb_find_change_buffering_value(
+/*===============================*/
+	const char*	input_name)	/*!< in: input change buffering
+					option name */
+{
+	ulint	use;
+
+	for (use = 0; use < UT_ARR_SIZE(innobase_change_buffering_values);
+	     use++) {
+		/* found a match */
+		if (!innobase_strcasecmp(
+			input_name, innobase_change_buffering_values[use])) {
+			return((ibuf_use_t)use);
+		}
+	}
+
+	/* Did not find any match */
+	return(IBUF_USE_COUNT);
+}
+
 /*************************************************************//**
 Check if it is a valid value of innodb_change_buffering. This function is
 registered as a callback with MySQL.
@@ -10370,19 +10398,22 @@ innodb_change_buffering_validate(
 	change_buffering_input = value->val_str(value, buff, &len);
 
 	if (change_buffering_input != NULL) {
-		ulint	use;
+		ibuf_use_t	use;
+
+		use = innodb_find_change_buffering_value(
+			change_buffering_input);
+
+		if (use != IBUF_USE_COUNT) {
+			/* Find a matching change_buffering option value. */
+			*static_cast<const char**>(save) =
+				innobase_change_buffering_values[use];
 
-		for (use = 0; use < UT_ARR_SIZE(innobase_change_buffering_values);
-		     use++) {
-			if (!innobase_strcasecmp(
-				    change_buffering_input,
-				    innobase_change_buffering_values[use])) {
-				*(ibuf_use_t*) save = (ibuf_use_t) use;
 			return(0);
 		}
 	}
-	}
 
+	/* No corresponding change buffering option for user supplied
+	"change_buffering_input" */
 	return(1);
 }
 
@@ -10396,18 +10427,24 @@ innodb_change_buffering_update(
 	THD*				thd,	/*!< in: thread handle */
 	struct st_mysql_sys_var*	var,	/*!< in: pointer to
 						system variable */
-	void*				var_ptr,	/*!< out: where the
+	void*				var_ptr,/*!< out: where the
 						formal string goes */
 	const void*			save)	/*!< in: immediate result
 						from check function */
 {
+	ibuf_use_t	use;
+
 	ut_a(var_ptr != NULL);
 	ut_a(save != NULL);
-	ut_a((*(ibuf_use_t*) save) < IBUF_USE_COUNT);
 
-	ibuf_use = *(const ibuf_use_t*) save;
+	use = innodb_find_change_buffering_value(
+		*static_cast<const char*const*>(save));
+
+	ut_a(use < IBUF_USE_COUNT);
 
-	*(const char**) var_ptr = innobase_change_buffering_values[ibuf_use];
+	ibuf_use = use;
+	*static_cast<const char**>(var_ptr) =
+		 *static_cast<const char*const*>(save);
 }
 
 static int show_innodb_vars(THD *thd, SHOW_VAR *var, char *buff)
@@ -10735,7 +10772,7 @@ static MYSQL_SYSVAR_STR(change_buffering, innobase_change_buffering,
   "Buffer changes to reduce random access: "
   "OFF, ON, none, inserts.",
   innodb_change_buffering_validate,
-  innodb_change_buffering_update, NULL);
+  innodb_change_buffering_update, "inserts"); 
 
 static MYSQL_SYSVAR_ULONG(read_ahead_threshold, srv_read_ahead_threshold,
   PLUGIN_VAR_RQCMDARG,