MDEV-26166 replace log_write_up_to(LSN_MAX,...) with log_buffer_flush_to_disk()

Also, remove comparison lsn > flush/write lsn, prior to calling
log_write_up_to. The checks and early returns are part of this function.

storage/innobase/buf/buf0dblwr.cc

@@ -681,8 +681,7 @@ void buf_dblwr_t::flush_buffered_writes_completed(const IORequest &request)
                                        static_cast<const byte*>(frame)));
     ut_ad(lsn);
     ut_ad(lsn >= bpage->oldest_modification());
-    if (lsn > log_sys.get_flushed_lsn())
-      log_write_up_to(lsn, true);
+    log_write_up_to(lsn, true);
     e.request.node->space->io(e.request, bpage->physical_offset(), e_size,
                               frame, bpage);
   }

storage/innobase/include/log0log.h

@@ -699,15 +699,6 @@ struct log_t{
 
   /** Shut down the redo log subsystem. */
   void close();
-
-  /** Initiate a write of the log buffer to the file if needed.
-  @param flush  whether to initiate a durable write */
-  inline void initiate_write(bool flush)
-  {
-    const lsn_t lsn= get_lsn();
-    if (!flush || get_flushed_lsn() < lsn)
-      log_write_up_to(lsn, flush);
-  }
 };
 
 /** Redo log system */

storage/innobase/log/log0log.cc

@@ -792,6 +792,7 @@ void log_write_up_to(lsn_t lsn, bool flush_to_disk, bool rotate_key)
 {
   ut_ad(!srv_read_only_mode);
   ut_ad(!rotate_key || flush_to_disk);
+  ut_ad(lsn != LSN_MAX);
 
   if (recv_no_ibuf_operations)
   {

storage/innobase/mtr/mtr0mtr.cc

@@ -689,7 +689,7 @@ static lsn_t log_reserve_and_open(size_t len)
     DEBUG_SYNC_C("log_buf_size_exceeded");
 
     /* Not enough free space, do a write of the log buffer */
-    log_sys.initiate_write(false);
+    log_write_up_to(log_sys.get_lsn(), false);
 
     srv_stats.log_waits.inc();
 

storage/innobase/row/row0mysql.cc

@@ -2989,13 +2989,13 @@ row_discard_tablespace_end(
 	}
 
 	DBUG_EXECUTE_IF("ib_discard_before_commit_crash",
-			log_write_up_to(LSN_MAX, true);
+			log_buffer_flush_to_disk();
 			DBUG_SUICIDE(););
 
 	trx_commit_for_mysql(trx);
 
 	DBUG_EXECUTE_IF("ib_discard_after_commit_crash",
-			log_write_up_to(LSN_MAX, true);
+			log_buffer_flush_to_disk();
 			DBUG_SUICIDE(););
 
 	row_mysql_unlock_data_dictionary(trx);

storage/innobase/srv/srv0srv.cc

@@ -1518,7 +1518,7 @@ srv_sync_log_buffer_in_background(void)
 	srv_main_thread_op_info = "flushing log";
 	if (difftime(current_time, srv_last_log_flush_time)
 	    >= srv_flush_log_at_timeout) {
-		log_sys.initiate_write(true);
+		log_buffer_flush_to_disk();
 		srv_last_log_flush_time = current_time;
 		srv_log_writes_and_flush++;
 	}

storage/innobase/srv/srv0start.cc

@@ -331,7 +331,7 @@ static dberr_t create_log_file(bool create_new_db, lsn_t lsn,
 	mysql_mutex_unlock(&log_sys.mutex);
 
 	log_make_checkpoint();
-	log_write_up_to(LSN_MAX, true);
+	log_buffer_flush_to_disk();
 
 	return DB_SUCCESS;
 }

storage/innobase/trx/trx0purge.cc

@@ -792,7 +792,7 @@ static void trx_purge_truncate_history()
 
 		DBUG_EXECUTE_IF("ib_undo_trunc",
 				ib::info() << "ib_undo_trunc";
-				log_write_up_to(LSN_MAX, true);
+				log_buffer_flush_to_disk();
 				DBUG_SUICIDE(););
 
 		for (ulint i = 0; i < TRX_SYS_N_RSEGS; ++i) {