Hi Yonghong,

I love your patch! Yet something to improve:

[auto build test ERROR on bpf-next/master]

url:    https://github.com/0day-ci/linux/commits/Yonghong-Song/implement-bpf-iterator-for-tcp-and-udp-sockets/20200623-090149
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
config: openrisc-defconfig (attached as .config)
compiler: or1k-linux-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
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=openrisc 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   or1k-linux-ld: net/core/filter.o: in function `bpf_skc_to_tcp_timewait_sock':
   filter.c:(.text+0x3e60): undefined reference to `tcpv6_prot'
>> or1k-linux-ld: filter.c:(.text+0x3e64): undefined reference to `tcpv6_prot'
   or1k-linux-ld: net/core/filter.o: in function `bpf_skc_to_tcp_request_sock':
   filter.c:(.text+0x3ee0): undefined reference to `tcpv6_prot'
   or1k-linux-ld: filter.c:(.text+0x3ee4): undefined reference to `tcpv6_prot'
   or1k-linux-ld: net/core/filter.o: in function `init_btf_sock_ids':
   filter.c:(.text+0x11384): undefined reference to `btf_find_by_name_kind'
   filter.c:(.text+0x11384): relocation truncated to fit: R_OR1K_INSN_REL_26 against undefined symbol `btf_find_by_name_kind'

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org