Hi Andrii, I love your patch! Perhaps something to improve: [auto build test WARNING on bpf-next/master] url: https://github.com/0day-ci/linux/commits/Andrii-Nakryiko/BPF-XDP-link/202... base: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master config: alpha-defconfig (attached as .config) compiler: alpha-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=alpha 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 >>): net/core/dev.c:8717:18: error: field 'link' has incomplete type 8717 | struct bpf_link link; | ^~~~ In file included from include/linux/instrumented.h:10, from include/linux/uaccess.h:5, from net/core/dev.c:71: net/core/dev.c: In function 'bpf_xdp_link_release': include/linux/kernel.h:1003:32: error: dereferencing pointer to incomplete type 'struct bpf_link' 1003 | BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \ | ^~~~~~ include/linux/compiler.h:372:9: note: in definition of macro '__compiletime_assert' 372 | if (!(condition)) \ | ^~~~~~~~~ include/linux/compiler.h:392:2: note: in expansion of macro '_compiletime_assert' 392 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | ^~~~~~~~~~~~~~~~~~~ include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert' 39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) | ^~~~~~~~~~~~~~~~~~ include/linux/kernel.h:1003:2: note: in expansion of macro 'BUILD_BUG_ON_MSG' 1003 | BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \ | ^~~~~~~~~~~~~~~~ include/linux/kernel.h:1003:20: note: in expansion of macro '__same_type' 1003 | BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \ | ^~~~~~~~~~~ net/core/dev.c:8972:34: note: in expansion of macro 'container_of' 8972 | struct bpf_xdp_link *xdp_link = container_of(link, struct bpf_xdp_link, link); | ^~~~~~~~~~~~ In file included from arch/alpha/include/asm/atomic.h:7, from include/linux/atomic.h:7, from include/linux/rcupdate.h:25, from include/linux/rculist.h:11, from include/linux/pid.h:5, from include/linux/sched.h:14, from include/linux/uaccess.h:6, from net/core/dev.c:71: net/core/dev.c: In function 'bpf_xdp_link_update': 48 | __typeof__(*(ptr)) _x_ = (x); \ | ^ net/core/dev.c:9026:13: note: in expansion of macro 'xchg' 9026 | old_prog = xchg(&link->prog, new_prog); | ^~~~ net/core/dev.c:9026:11: warning: assignment to 'struct bpf_prog *' from 'int' makes pointer from integer without a cast [-Wint-conversion] 9026 | old_prog = xchg(&link->prog, new_prog); | ^ net/core/dev.c: At top level: net/core/dev.c:9034:21: error: variable 'bpf_xdp_link_lops' has initializer but incomplete type 9034 | static const struct bpf_link_ops bpf_xdp_link_lops = { | ^~~~~~~~~~~~ net/core/dev.c:9035:3: error: 'const struct bpf_link_ops' has no member named 'release' 9035 | .release = bpf_xdp_link_release, | ^~~~~~~ net/core/dev.c:9035:13: warning: excess elements in struct initializer 9035 | .release = bpf_xdp_link_release, | ^~~~~~~~~~~~~~~~~~~~ net/core/dev.c:9035:13: note: (near initialization for 'bpf_xdp_link_lops') net/core/dev.c:9036:3: error: 'const struct bpf_link_ops' has no member named 'dealloc' 9036 | .dealloc = bpf_xdp_link_dealloc, | ^~~~~~~ net/core/dev.c:9036:13: warning: excess elements in struct initializer 9036 | .dealloc = bpf_xdp_link_dealloc, | ^~~~~~~~~~~~~~~~~~~~ net/core/dev.c:9036:13: note: (near initialization for 'bpf_xdp_link_lops') net/core/dev.c:9037:3: error: 'const struct bpf_link_ops' has no member named 'update_prog' 9037 | .update_prog = bpf_xdp_link_update, | ^~~~~~~~~~~ net/core/dev.c:9037:17: warning: excess elements in struct initializer 9037 | .update_prog = bpf_xdp_link_update, | ^~~~~~~~~~~~~~~~~~~ net/core/dev.c:9037:17: note: (near initialization for 'bpf_xdp_link_lops') net/core/dev.c: In function 'bpf_xdp_link_attach': net/core/dev.c:9043:25: error: storage size of 'link_primer' isn't known 9043 | struct bpf_link_primer link_primer; | ^~~~~~~~~~~ net/core/dev.c:9058:2: error: implicit declaration of function 'bpf_link_init'; did you mean 'bio_list_init'? [-Werror=implicit-function-declaration] 9058 | bpf_link_init(&link->link, BPF_LINK_TYPE_XDP, &bpf_xdp_link_lops, prog); | ^~~~~~~~~~~~~ | bio_list_init net/core/dev.c:9062:8: error: implicit declaration of function 'bpf_link_prime' [-Werror=implicit-function-declaration] 9062 | err = bpf_link_prime(&link->link, &link_primer); | ^~~~~~~~~~~~~~ net/core/dev.c:9073:3: error: implicit declaration of function 'bpf_link_cleanup' [-Werror=implicit-function-declaration] 9073 | bpf_link_cleanup(&link_primer); | ^~~~~~~~~~~~~~~~ net/core/dev.c:9077:7: error: implicit declaration of function 'bpf_link_settle' [-Werror=implicit-function-declaration] 9077 | fd = bpf_link_settle(&link_primer); | ^~~~~~~~~~~~~~~ net/core/dev.c:9043:25: warning: unused variable 'link_primer' [-Wunused-variable] 9043 | struct bpf_link_primer link_primer; | ^~~~~~~~~~~ net/core/dev.c: At top level: net/core/dev.c:9034:34: error: storage size of 'bpf_xdp_link_lops' isn't known 9034 | static const struct bpf_link_ops bpf_xdp_link_lops = { | ^~~~~~~~~~~~~~~~~ cc1: some warnings being treated as errors vim +48 arch/alpha/include/asm/cmpxchg.h 5ba840f9da1ff9 Paul Gortmaker 2012-04-02 40 fbfcd019917098 Andrea Parri 2018-02-27 41 /* fbfcd019917098 Andrea Parri 2018-02-27 42 * The leading and the trailing memory barriers guarantee that these fbfcd019917098 Andrea Parri 2018-02-27 43 * operations are fully ordered. fbfcd019917098 Andrea Parri 2018-02-27 44 */ 5ba840f9da1ff9 Paul Gortmaker 2012-04-02 45 #define xchg(ptr, x) \ 5ba840f9da1ff9 Paul Gortmaker 2012-04-02 46 ({ \ fbfcd019917098 Andrea Parri 2018-02-27 47 __typeof__(*(ptr)) __ret; \ 5ba840f9da1ff9 Paul Gortmaker 2012-04-02 @48 __typeof__(*(ptr)) _x_ = (x); \ fbfcd019917098 Andrea Parri 2018-02-27 49 smp_mb(); \ fbfcd019917098 Andrea Parri 2018-02-27 50 __ret = (__typeof__(*(ptr))) \ fbfcd019917098 Andrea Parri 2018-02-27 51 __xchg((ptr), (unsigned long)_x_, sizeof(*(ptr))); \ fbfcd019917098 Andrea Parri 2018-02-27 52 smp_mb(); \ fbfcd019917098 Andrea Parri 2018-02-27 53 __ret; \ 5ba840f9da1ff9 Paul Gortmaker 2012-04-02 54 }) 5ba840f9da1ff9 Paul Gortmaker 2012-04-02 55 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org