bionic 的 libc/kernel/common/linux/in6.h 有一句：

 ***   This header was automatically generated from a Linux kernel header
 ***   of the same name, to make information necessary for userspace to
 ***   call into the kernel available to libc.  It contains only constants,
 ***   structures, and macros generated from the original header, and thus,
 ***   contains no copyrightable information.
 ***
 ***   To edit the content of this header, modify the corresponding
 ***   source file (e.g. under external/kernel-headers/original/) then
 ***   run bionic/libc/kernel/tools/update_all.py