+/* WARNING: Be careful with file system ioctls! When we get an fd, we
+ * need to make sure it either refers to only a regular file or
+ * directory, or that it is located on btrfs, before invoking any
+ * btrfs ioctls. The ioctl numbers are reused by some device drivers
+ * (such as DRM), and hence might have bad effects when invoked on
+ * device nodes (that reference drivers) rather than fds to normal
+ * files or directories. */
+