+#define COPY_BUFFER_SIZE (16*1024u)
+
+static ssize_t try_copy_file_range(int fd_in, loff_t *off_in,
+ int fd_out, loff_t *off_out,
+ size_t len,
+ unsigned int flags) {
+ static int have = -1;
+ ssize_t r;
+
+ if (have == false)
+ return -ENOSYS;
+
+ r = copy_file_range(fd_in, off_in, fd_out, off_out, len, flags);
+ if (_unlikely_(have < 0))
+ have = r >= 0 || errno != ENOSYS;
+ if (r >= 0)
+ return r;
+ else
+ return -errno;
+}