netdev - Re: [PATCH bpf-next v2 1/7] bpf/flow_dissector: pass input flags to BPF flow dissector program

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Date:   Thu, 25 Jul 2019 12:58:57 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, davem@...emloft.net,
        ast@...nel.org, daniel@...earbox.net,
        Willem de Bruijn <willemb@...gle.com>,
        Song Liu <songliubraving@...com>,
        Petar Penkov <ppenkov@...gle.com>
Subject: Re: [PATCH bpf-next v2 1/7] bpf/flow_dissector: pass input flags to
 BPF flow dissector program

On Thu, Jul 25, 2019 at 08:33:36AM -0700, Stanislav Fomichev wrote:
> C flow dissector supports input flags that tell it to customize parsing
> by either stopping early or trying to parse as deep as possible. Pass
> those flags to the BPF flow dissector so it can make the same
> decisions. In the next commits I'll add support for those flags to
> our reference bpf_flow.c
> 
> Acked-by: Willem de Bruijn <willemb@...gle.com>
> Acked-by: Song Liu <songliubraving@...com>
> Cc: Song Liu <songliubraving@...com>
> Cc: Willem de Bruijn <willemb@...gle.com>
> Cc: Petar Penkov <ppenkov@...gle.com>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
>  include/linux/skbuff.h       | 2 +-
>  include/net/flow_dissector.h | 4 ----
>  include/uapi/linux/bpf.h     | 5 +++++
>  net/bpf/test_run.c           | 2 +-
>  net/core/flow_dissector.c    | 5 +++--
>  5 files changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 718742b1c505..9b7a8038beec 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -1271,7 +1271,7 @@ static inline int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr)
>  
>  struct bpf_flow_dissector;
>  bool bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx,
> -		      __be16 proto, int nhoff, int hlen);
> +		      __be16 proto, int nhoff, int hlen, unsigned int flags);
>  
>  bool __skb_flow_dissect(const struct net *net,
>  			const struct sk_buff *skb,
> diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
> index 90bd210be060..3e2642587b76 100644
> --- a/include/net/flow_dissector.h
> +++ b/include/net/flow_dissector.h
> @@ -253,10 +253,6 @@ enum flow_dissector_key_id {
>  	FLOW_DISSECTOR_KEY_MAX,
>  };
>  
> -#define FLOW_DISSECTOR_F_PARSE_1ST_FRAG		BIT(0)
> -#define FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL	BIT(1)
> -#define FLOW_DISSECTOR_F_STOP_AT_ENCAP		BIT(2)
> -
>  struct flow_dissector_key {
>  	enum flow_dissector_key_id key_id;
>  	size_t offset; /* offset of struct flow_dissector_key_*
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index fa1c753dcdbc..b4ad19bd6aa8 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3507,6 +3507,10 @@ enum bpf_task_fd_type {
>  	BPF_FD_TYPE_URETPROBE,		/* filename + offset */
>  };
>  
> +#define FLOW_DISSECTOR_F_PARSE_1ST_FRAG		(1U << 0)
> +#define FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL	(1U << 1)
> +#define FLOW_DISSECTOR_F_STOP_AT_ENCAP		(1U << 2)
> +

I'm a bit concerned with direct move.
Last time we were in similar situation we've created:
enum {
        BPF_TCP_ESTABLISHED = 1,
        BPF_TCP_SYN_SENT,

and added:
        BUILD_BUG_ON((int)BPF_TCP_ESTABLISHED != (int)TCP_ESTABLISHED);
        BUILD_BUG_ON((int)BPF_TCP_SYN_SENT != (int)TCP_SYN_SENT);

It may be overkill here, but feels safer than direct move.
Adding BPF_ prefix also feels necessary to avoid very unlikely
(but still theoretically possible) conflicts.