On Tue, Jun 23, 2020 at 09:17:49AM -0700, Yonghong Song wrote:
> bpf iterator implments traversal of kernel data structures and these
> data structures are passed to a bpf program for processing.
> This gives great flexibility for users to examine kernel data
> structure without using e.g. /proc/net which has limited and
> fixed format.
>
> Commit 138d0be35b14 ("net: bpf: Add netlink and ipv6_route bpf_iter targets")
> implemented bpf iterators for netlink and ipv6_route.
> This patch set intends to implement bpf iterators for tcp and udp.
>
> Currently, /proc/net/tcp is used to print tcp4 stats and /proc/net/tcp6
> is used to print tcp6 stats. /proc/net/udp[6] have similar usage model.
> In contrast, only one tcp iterator is implemented and it is bpf program
> resposibility to filter based on socket family. The same is for udp.
> This will avoid another unnecessary traversal pass if users want
> to check both tcp4 and tcp6.
>
> Several helpers are also implemented in this patch
> bpf_skc_to_{tcp, tcp6, tcp_timewait, tcp_request, udp6}_sock
> The argument for these helpers is not a fixed btf_id. For example,
> bpf_skc_to_tcp(struct sock_common *), or
> bpf_skc_to_tcp(struct sock *), or
> bpf_skc_to_tcp(struct inet_sock *), ...
> are all valid. At runtime, the helper will check whether pointer cast
> is legal or not. Please see Patch #5 for details.
>
> Since btf_id's for both arguments and return value are known at
> build time, the btf_id's are pre-computed once vmlinux btf becomes
> valid. Jiri's "adding d_path helper" patch set
> https://lore.kernel.org/bpf/20200616100512.2168860-1-jolsa@xxxxxxxxxx/T/
> provides a way to pre-compute btf id during vmlinux build time.
> This can be applied here as well. A followup patch can convert
> to build time btf id computation after Jiri's patch landed.
>
> Changelogs:
> v3 -> v4:
> - fix bpf_skc_to_{tcp_timewait, tcp_request} helper implementation
> as just checking sk->sk_state is not enough (Martin)
> - fix a few kernel test robot reported failures
> - move bpf_tracing_net.h from libbpf to selftests (Andrii)
> - remove __weak attribute from selftests CONFIG_HZ variables (Andrii)
> v2 -> v3:
> - change sock_cast*/SOCK_CAST* names to btf_sock* names for generality (Martin)
> - change gpl_license to false (Martin)
> - fix helper to cast to tcp timewait/request socket. (Martin)
> v1 -> v2:
> - guard init_sock_cast_types() defination properly with CONFIG_NET (Martin)
> - reuse the btf_ids, computed for new helper argument, for return
> values (Martin)
> - using BTF_TYPE_EMIT to express intent of btf type generation (Andrii)
> - abstract out common net macros into bpf_tracing_net.h (Andrii)
Acked-by: Martin KaFai Lau <kafai@xxxxxx>
