redo log mics fixes

os_file_flush_data_func(): fix builds on POSIX OSs where fdatasync()
is not avaiable

log_t::files::flush_data_only(): rename from fdatasync()

log_t::files::fsync(): removed and replaced with flush_data_only().
It will flush everything we need for using redo log files.

storage/innobase/handler/ha_innodb.cc

@@ -18614,7 +18614,7 @@ checkpoint_now_set(THD*, st_mysql_sys_var*, void*, const void* save)
 			  ? log_sys.append_on_checkpoint->size() : 0)
 		       < log_sys.lsn) {
 			log_make_checkpoint();
-			log_sys.log.fdatasync();
+			log_sys.log.flush_data_only();
 		}
 
 		dberr_t err = fil_write_flushed_lsn(log_sys.lsn);

storage/innobase/include/log0log.h

@@ -553,10 +553,8 @@ struct log_t{
     @param[in]	total_offset	offset in log files treated as a single file
     @param[in]	buf		buffer from which to write */
     void write(size_t total_offset, span<byte> buf);
-    /** flushes OS page cache for all log files */
-    void fsync();
     /** flushes OS page cache (excluding metadata!) for all log files */
-    void fdatasync();
+    void flush_data_only();
     /** closes all log files */
     void close_files();
 

storage/innobase/log/log0log.cc

@@ -641,24 +641,7 @@ void log_t::files::write(size_t total_offset, span<byte> buf)
   }
 }
 
-void log_t::files::fsync()
-{
-  ut_ad(files.size() == file_names.size());
-
-  log_sys.pending_flushes.fetch_add(1, std::memory_order_acquire);
-  for (auto it= files.begin(), end= files.end(); it != end; ++it)
-  {
-    if (!os_file_flush(*it))
-    {
-      const auto idx= std::distance(files.begin(), it);
-      ib::fatal() << "os_file_flush(" << file_names[idx] << ") failed";
-    }
-  }
-  log_sys.pending_flushes.fetch_sub(1, std::memory_order_release);
-  log_sys.flushes.fetch_add(1, std::memory_order_release);
-}
-
-void log_t::files::fdatasync()
+void log_t::files::flush_data_only()
 {
   ut_ad(files.size() == file_names.size());
 
@@ -880,7 +863,7 @@ log_write_flush_to_disk_low()
 	calling os_event_set()! */
 	ut_a(log_sys.n_pending_flushes == 1); /* No other threads here */
 
-	log_sys.log.fdatasync();
+	log_sys.log.flush_data_only();
 
 	log_mutex_enter();
 	log_sys.flushed_to_disk_lsn = log_sys.current_flush_lsn;
@@ -1307,7 +1290,7 @@ void log_write_checkpoint_info(lsn_t end_lsn)
 							   : LOG_CHECKPOINT_1,
 			  {buf, OS_FILE_LOG_BLOCK_SIZE});
 
-	log_sys.log.fdatasync();
+	log_sys.log.flush_data_only();
 
 	log_mutex_enter();
 
@@ -1785,7 +1768,7 @@ logs_empty_and_mark_files_at_shutdown(void)
 
 		/* Ensure that all buffered changes are written to the
 		redo log before fil_close_all_files(). */
-		log_sys.log.fdatasync();
+		log_sys.log.flush_data_only();
 	} else {
 		lsn = srv_start_lsn;
 	}

storage/innobase/os/os0file.cc

@@ -4626,7 +4626,7 @@ os_normalize_path(
 }
 
 bool os_file_flush_data_func(os_file_t file) {
-#ifdef _WIN32
+#if defined(_WIN32) || !defined(HAVE_FDATASYNC) || HAVE_DECL_FDATASYNC == 0
   return os_file_flush_func(file);
 #else
   bool success= fdatasync(file) != -1;

storage/innobase/srv/srv0start.cc

@@ -421,7 +421,7 @@ MY_ATTRIBUTE((warn_unused_result, nonnull))
 static dberr_t create_log_files_rename(char *logfilename, size_t dirnamelen,
                                        lsn_t lsn, std::string &logfile0)
 {
-  log_sys.log.fsync();
+  log_sys.log.flush_data_only();
 
   ut_ad(!srv_log_files_created);
   ut_d(srv_log_files_created= true);
@@ -1132,7 +1132,7 @@ srv_prepare_to_delete_redo_log_files(
 
 		log_write_up_to(flushed_lsn, true);
 
-		log_sys.log.fsync();
+		log_sys.log.flush_data_only();
 
 		ut_ad(flushed_lsn == log_get_lsn());