On 12/20/2018 09:05 PM, Quentin Monnet wrote: > 2018-12-20 18:25 UTC+0100 ~ Daniel Borkmann <dan...@iogearbox.net> >> On 12/20/2018 01:24 PM, Quentin Monnet wrote: >>> Make bpftool able to dump a subset of the parameters collected by >>> probing the system as a listing of C-style #define macros, so that >>> external projects can reuse the result of this probing and build >>> BPF-based project in accordance with the features available on the >>> system. >>> >>> The new "macros" keyword is used to select this output. An additional >>> "prefix" keyword is added so that users can select a custom prefix for >>> macro names, in order to avoid any namespace conflict. >>> >>> Sample output: >>> >>> # bpftool feature probe kernel macros prefix FOO_ >>> /*** System call availability ***/ >>> #define FOO_HAVE_BPF_SYSCALL >>> >>> /*** eBPF program types ***/ >>> #define FOO_HAVE_SOCKET_FILTER_PROG_TYPE >>> #define FOO_HAVE_KPROBE_PROG_TYPE >>> #define FOO_HAVE_SCHED_CLS_PROG_TYPE >>> ... >>> >>> /*** eBPF map types ***/ >>> #define FOO_HAVE_HASH_MAP_TYPE >>> #define FOO_HAVE_ARRAY_MAP_TYPE >>> #define FOO_HAVE_PROG_ARRAY_MAP_TYPE >>> ... >>> >>> /*** eBPF helper functions ***/ >>> ... >>> #define FOO_BPF_SKB_CHANGE_HEAD_HELPER_COMPAT_LIST "" \ >>> "lwt_xmit " \ >>> "sk_skb " >>> #define FOO_BPF_XDP_ADJUST_HEAD_HELPER_COMPAT_LIST "" \ >>> "xdp " >>> #define FOO_BPF_PROBE_READ_STR_HELPER_COMPAT_LIST "" \ >>> "kprobe " \ >>> "tracepoint " \ >>> "perf_event " \ >>> "raw_tracepoint " >>> ... >> >> Rest looks good to me, just a comment here. How would programs use the >> compat list? Wouldn't it be nicer to provide a PROG(HELPER) availability >> query along the lines of ... >> >> #if FOO_HAVE_SOCKET_FILTER(skb_load_bytes) == 1 >> // ... >> #endif >> >> ... where the helper provides these macro functions and results in the >> header file? So they can be used easily in the code from BPF prog or >> normal C applications? > > I was thinking about strstr() here, but it is true it is limited to runtime > and will not work with the preprocessor :s. > > How would you dump parameters to make your PROG(HELPER) work? Something along > the following? > > #define BPF__PROG_TYPE_SOCKET_FILTER__HELPER_skb_load_bytes 1 > #define BPF__PROG_TYPE_SOCKET_FILTER__HELPER_bind 0 > ... > > #define HAVE_SOCKET_FILTER_HELPER(name) \ > BPF__PROG_TYPE_SOCKET_FILTER__HELPER_ ## name > > or even > > #define HAVE_PROG_TYPE_HELPER(type, helper) \ > BPF__PROG_TYPE_ ## type ## __HELPER_ ## helper > > Does that correspond to what you have in mind?
Yeah, something like this; slight preference to the latter. Thanks, Daniel
