MDEV-24685 fixup: Remove srv_n_file_io_threads

The variable was not really being used for anything. The parameters
innodb_read_io_threads, innodb_write_io_threads have replaced
innodb_file_io_threads.

extra/mariabackup/xtrabackup.cc

@@ -2091,7 +2091,6 @@ static bool innodb_init_param()
 	srv_buf_pool_size = (ulint) xtrabackup_use_memory;
 	srv_buf_pool_chunk_unit = (ulong)srv_buf_pool_size;
 
-	srv_n_file_io_threads = (uint) innobase_file_io_threads;
 	srv_n_read_io_threads = (uint) innobase_read_io_threads;
 	srv_n_write_io_threads = (uint) innobase_write_io_threads;
 
@@ -4486,7 +4485,6 @@ static bool xtrabackup_backup_func()
 	xb_filters_init();
 
 	xb_fil_io_init();
-	srv_n_file_io_threads = srv_n_read_io_threads;
 
 	if (os_aio_init()) {
 		msg("Error: cannot initialize AIO subsystem");
@@ -5965,12 +5963,6 @@ static bool xtrabackup_prepare_func(char** argv)
 
 	fil_system.freeze_space_list = 0;
 
-	/* increase IO threads */
-	if (srv_n_file_io_threads < 10) {
-		srv_n_read_io_threads = 4;
-		srv_n_write_io_threads = 4;
-	}
-
 	msg("Starting InnoDB instance for recovery.");
 
 	msg("mariabackup: Using %lld bytes for buffer pool "

storage/innobase/include/srv0srv.h

@@ -313,7 +313,6 @@ extern ulong srv_buf_pool_load_pages_abort;
 /** Lock table size in bytes */
 extern ulint	srv_lock_table_size;
 
-extern uint	srv_n_file_io_threads;
 extern my_bool	srv_random_read_ahead;
 extern ulong	srv_read_ahead_threshold;
 extern uint	srv_n_read_io_threads;
@@ -434,8 +433,6 @@ extern bool	srv_log_file_created;
 
 extern ulint	srv_dml_needed_delay;
 
-#define SRV_MAX_N_IO_THREADS	130
-
 /** innodb_purge_threads; the number of purge tasks to use */
 extern uint srv_n_purge_threads;
 

storage/innobase/srv/srv0start.cc

@@ -110,9 +110,6 @@ lsn_t	srv_shutdown_lsn;
 /** TRUE if a raw partition is in use */
 ibool	srv_start_raw_disk_in_use;
 
-/** Number of IO threads to use */
-uint	srv_n_file_io_threads;
-
 /** UNDO tablespaces starts with space id. */
 ulint	srv_undo_space_id_start;
 
@@ -1208,18 +1205,11 @@ dberr_t srv_start(bool create_new_db)
 		return(srv_init_abort(err));
 	}
 
-	srv_n_file_io_threads = srv_n_read_io_threads + srv_n_write_io_threads;
-
-	if (!srv_read_only_mode) {
-		/* Add the log and ibuf IO threads. */
-		srv_n_file_io_threads += 2;
-	} else {
+	if (srv_read_only_mode) {
 		ib::info() << "Disabling background log and ibuf IO write"
 			<< " threads.";
 	}
 
-	ut_a(srv_n_file_io_threads <= SRV_MAX_N_IO_THREADS);
-
 	if (os_aio_init()) {
 		ib::error() << "Cannot initialize AIO sub-system";