MDEV-11687 innodb_use_fallocate has no effect

Deprecate the variable in MariaDB 10.2, saying
that it will be removed in 10.3.

mysql-test/suite/sys_vars/r/sysvars_innodb.result

@@ -2595,6 +2595,20 @@ NUMERIC_BLOCK_SIZE	NULL
 ENUM_VALUE_LIST	OFF,ON
 READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	NONE
+VARIABLE_NAME	INNODB_USE_FALLOCATE
+SESSION_VALUE	NULL
+GLOBAL_VALUE	OFF
+GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+DEFAULT_VALUE	OFF
+VARIABLE_SCOPE	GLOBAL
+VARIABLE_TYPE	BOOLEAN
+VARIABLE_COMMENT	Use posix_fallocate() to allocate files. DEPRECATED, has no effect.
+NUMERIC_MIN_VALUE	NULL
+NUMERIC_MAX_VALUE	NULL
+NUMERIC_BLOCK_SIZE	NULL
+ENUM_VALUE_LIST	OFF,ON
+READ_ONLY	YES
+COMMAND_LINE_ARGUMENT	NONE
 VARIABLE_NAME	INNODB_USE_MTFLUSH
 SESSION_VALUE	NULL
 GLOBAL_VALUE	OFF

storage/innobase/handler/ha_innodb.cc

@@ -250,6 +250,7 @@ values */
 static ulong	innobase_fast_shutdown			= 1;
 static my_bool	innobase_file_format_check		= TRUE;
 static my_bool	innobase_use_atomic_writes		= FALSE;
+static my_bool	innobase_use_fallocate;
 static my_bool	innobase_use_doublewrite		= TRUE;
 static my_bool	innobase_use_checksums			= TRUE;
 static my_bool	innobase_locks_unsafe_for_binlog	= FALSE;
@@ -4637,6 +4638,13 @@ innobase_init(
 	data_mysql_default_charset_coll = (ulint) default_charset_info->number;
 
 	innobase_commit_concurrency_init_default();
+
+	if (innobase_use_fallocate) {
+		ib::warn() << "innodb_use_fallocate is DEPRECATED"
+			" and has no effect in MariaDB 10.2."
+			" It will be removed in MariaDB 10.3.";
+	}
+
 	srv_use_atomic_writes = (ibool) innobase_use_atomic_writes;
 	if (innobase_use_atomic_writes) {
 		fprintf(stderr, "InnoDB: using atomic writes.\n");
@@ -21947,6 +21955,11 @@ static MYSQL_SYSVAR_BOOL(use_atomic_writes, innobase_use_atomic_writes,
   "on Linux only with FusionIO device, and directFS filesystem.",
   NULL, NULL, FALSE);
 
+static MYSQL_SYSVAR_BOOL(use_fallocate, innobase_use_fallocate,
+  PLUGIN_VAR_NOCMDARG | PLUGIN_VAR_READONLY,
+  "Use posix_fallocate() to allocate files. DEPRECATED, has no effect.",
+  NULL, NULL, FALSE);
+
 static MYSQL_SYSVAR_ULONG(io_capacity, srv_io_capacity,
   PLUGIN_VAR_RQCMDARG,
   "Number of IOPs the server can do. Tunes the background IO rate",
@@ -23178,6 +23191,7 @@ static struct st_mysql_sys_var* innobase_system_variables[]= {
   MYSQL_SYSVAR(data_home_dir),
   MYSQL_SYSVAR(doublewrite),
   MYSQL_SYSVAR(use_atomic_writes),
+  MYSQL_SYSVAR(use_fallocate),
   MYSQL_SYSVAR(api_enable_binlog),
   MYSQL_SYSVAR(api_enable_mdl),
   MYSQL_SYSVAR(api_disable_rowlock),