+#if defined HAVE_FALLOCATE || HAVE_SYS_FALLOCATE
+#ifdef HAVE_LINUX_FALLOC_H
+#include <linux/falloc.h>
+#endif
+#ifdef FALLOC_FL_KEEP_SIZE
+#define SUPPORT_PREALLOCATION 1
+#elif defined HAVE_FTRUNCATE
+#define SUPPORT_PREALLOCATION 1
+#define PREALLOCATE_NEEDS_TRUNCATE 1
+#endif
+#else /* !fallocate */
+#if defined HAVE_EFFICIENT_POSIX_FALLOCATE && defined HAVE_FTRUNCATE
+#define SUPPORT_PREALLOCATION 1
+#define PREALLOCATE_NEEDS_TRUNCATE 1
+#endif
+#endif
+