Hi Changbin, I love your patch! Perhaps something to improve: [auto build test WARNING on lwn/docs-next] [also build test WARNING on linus/master v5.13-rc5 next-20210604] [cannot apply to v9fs/for-next] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch] url: https://github.com/0day-ci/linux/commits/Changbin-Du/9p-add-support-for-r... base: git://git.lwn.net/linux-2.6 docs-next config: arm-allyesconfig (attached as .config) compiler: arm-linux-gnueabi-gcc (GCC) 9.3.0 reproduce (this is a W=1 build): wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross # https://github.com/0day-ci/linux/commit/96098f751038703cc0fda4f018236d240... git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review Changbin-Du/9p-add-support-for-root-file-systems/20210607-071229 git checkout 96098f751038703cc0fda4f018236d240a86930d # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=arm If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; All warnings (new ones prefixed by >>): >> fs/9p/v9fsroot.c:53:12: warning: no previous prototype for 'v9fs_root_data' [-Wmissing-prototypes] 53 | int __init v9fs_root_data(char **dev, char **opts) | ^~~~~~~~~~~~~~

vim +/v9fs_root_data +53 fs/9p/v9fsroot.c 52 > 53 int __init v9fs_root_data(char **dev, char **opts) --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org