Re: [PATCH bpf-next] bpf: add read/write access to skb->tstamp from tc clsact progs

[Alexei Starovoitov]

On Tue, Nov 20, 2018 at 07:18:48PM -0500, Vlad Dumitrescu wrote:
> This could be used to rate limit egress traffic in concert with a qdisc
> which supports Earliest Departure Time, such as FQ.
> 
> Signed-off-by: Vlad Dumitrescu <vla...@google.com>
> ---
>  include/uapi/linux/bpf.h                    |  1 +
>  net/core/filter.c                           | 26 +++++++++++++++++++++
>  tools/include/uapi/linux/bpf.h              |  1 +
>  tools/testing/selftests/bpf/test_verifier.c |  4 ++++
>  4 files changed, 32 insertions(+)
> 
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index c1554aa074659..23e2031a43d43 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2468,6 +2468,7 @@ struct __sk_buff {
>  
>       __u32 data_meta;
>       struct bpf_flow_keys *flow_keys;
> +     __u64 tstamp;
>  };
>  
>  struct bpf_tunnel_key {
> diff --git a/net/core/filter.c b/net/core/filter.c
> index f6ca38a7d4332..c45155c8e519c 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -5573,6 +5573,10 @@ static bool bpf_skb_is_valid_access(int off, int size, 
> enum bpf_access_type type
>               if (size != sizeof(struct bpf_flow_keys *))
>                       return false;
>               break;
> +     case bpf_ctx_range(struct __sk_buff, tstamp):
> +             if (size != sizeof(__u64))
> +                     return false;
> +             break;
>       default:
>               /* Only narrow read access allowed for now. */
>               if (type == BPF_WRITE) {
> @@ -5600,6 +5604,7 @@ static bool sk_filter_is_valid_access(int off, int size,
>       case bpf_ctx_range(struct __sk_buff, data_end):
>       case bpf_ctx_range(struct __sk_buff, flow_keys):
>       case bpf_ctx_range_till(struct __sk_buff, family, local_port):
> +     case bpf_ctx_range(struct __sk_buff, tstamp):
>               return false;
>       }
>  
> @@ -5624,6 +5629,7 @@ static bool cg_skb_is_valid_access(int off, int size,
>       case bpf_ctx_range(struct __sk_buff, tc_classid):
>       case bpf_ctx_range(struct __sk_buff, data_meta):
>       case bpf_ctx_range(struct __sk_buff, flow_keys):
> +     case bpf_ctx_range(struct __sk_buff, tstamp):
>               return false;

looks good to me.

Any particular reason you decided to disable it for cg_skb ?
It seems to me the same EDT approach will work from
cgroup-bpf skb hooks just as well and then we can have neat
way of controlling traffic per-container instead of tc-clsbpf global.
If you're already on cgroup v2 it will save you a lot of classifier
cycles, since you'd be able to group apps by cgroup
instead of relying on ip only.