netdev - Re: [PATCH bpf-next 2/3] bpf: add BPF_PROG_TEST

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Message-ID: <20190124035600.ag4d7glkyysiluuu@ast-mbp.dhcp.thefacebook.com>
Date:   Wed, 23 Jan 2019 19:57:34 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, ast@...nel.org,
        daniel@...earbox.net
Subject: Re: [PATCH bpf-next 2/3] bpf: add BPF_PROG_TEST_RUN support for flow
 dissector

On Tue, Jan 22, 2019 at 01:23:14PM -0800, Stanislav Fomichev wrote:
> The input is packet data, the output is struct bpf_flow_key. This should
> make it easy to test flow dissector programs without elaborate
> setup.
> 
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
>  include/linux/bpf.h |  3 ++
>  net/bpf/test_run.c  | 75 ++++++++++++++++++++++++++++++++++++++++++++-
>  net/core/filter.c   |  1 +
>  3 files changed, 78 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index e734f163bd0b..701ef954a258 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -397,6 +397,9 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
>  			  union bpf_attr __user *uattr);
>  int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
>  			  union bpf_attr __user *uattr);
> +int bpf_prog_test_run_flow_dissector(struct bpf_prog *prog,
> +				     const union bpf_attr *kattr,
> +				     union bpf_attr __user *uattr);
>  
>  /* an array of programs to be executed under rcu_lock.
>   *
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index fa2644d276ef..ecad72885f23 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -16,12 +16,26 @@
>  static __always_inline u32 bpf_test_run_one(struct bpf_prog *prog, void *ctx,
>  		struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE])
>  {
> +	struct bpf_skb_data_end *cb;
> +	struct sk_buff *skb;
>  	u32 ret;
>  
>  	preempt_disable();
>  	rcu_read_lock();
>  	bpf_cgroup_storage_set(storage);
> -	ret = BPF_PROG_RUN(prog, ctx);
> +
> +	switch (prog->type) {
> +	case BPF_PROG_TYPE_FLOW_DISSECTOR:
> +		skb = (struct sk_buff *)ctx;
> +		cb = (struct bpf_skb_data_end *)skb->cb;
> +		ret = __skb_flow_bpf_dissect(prog, ctx, &flow_keys_dissector,
> +					     cb->qdisc_cb.flow_keys);
> +		break;
> +	default:
> +		ret = BPF_PROG_RUN(prog, ctx);
> +		break;
> +	}

What is the benefit of this minimal code reuse?
It seems to me bpf_test_run_one() gets slower for all,
since prog type needs to be checked before every prog run.
The point of bpf_prog_ops->test_run was to avoid this overhead.
Are you somehow expecting flow_dissector prog using cgroup local storage?
I don't think that's possible.