Remove insufficient locking on Apple

Author: dr-m

storage/innobase/handler/backup_innodb.cc

@@ -574,12 +574,13 @@ class InnoDB_backup
 #else
       int f;
 # ifdef __APPLE__
-      backup_batch_start(node->space,
-                         (node->space->size +
-                          fil_space_t::BACKUP_BATCH_SIZE - 1) &
-                         ~fil_space_t::BACKUP_BATCH_SIZE);
+      /* aio::synchronous() in another thread may concurrently invoke
+      pwrite(2) on node->handle. We assume that both pwrite(2) and
+      fclonefileat(2) are atomic with respect to each other. Should
+      this assumption be invalid, some data files in the backup may be
+      corrupted. This corruption can be fixed by either removing this
+      special handling, or by implementing file-level locking. */
       f= fclonefileat(node->handle, target, node->name, 0);
-      backup_batch_stop(node->space);
       if (!f)
         break;
       switch (errno) {