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Date:   Wed, 18 Nov 2020 16:11:54 -0800
From:   Martin KaFai Lau <kafai@fb.com>
To:     Kuniyuki Iwashima <kuniyu@amazon.co.jp>
CC:     "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Benjamin Herrenschmidt <benh@amazon.com>,
        Kuniyuki Iwashima <kuni1840@gmail.com>, <bpf@vger.kernel.org>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH bpf-next 6/8] bpf: Add cookie in sk_reuseport_md.
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On Tue, Nov 17, 2020 at 06:40:21PM +0900, Kuniyuki Iwashima wrote:
> We will call sock_reuseport.prog for socket migration in the next commit,
> so the eBPF program has to know which listener is closing in order to
> select the new listener.
> 
> Currently, we can get a unique ID for each listener in the userspace by
> calling bpf_map_lookup_elem() for BPF_MAP_TYPE_REUSEPORT_SOCKARRAY map.
> This patch exposes the ID to the eBPF program.
> 
> Reviewed-by: Benjamin Herrenschmidt <benh@amazon.com>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
> ---
>  include/linux/bpf.h            | 1 +
>  include/uapi/linux/bpf.h       | 1 +
>  net/core/filter.c              | 8 ++++++++
>  tools/include/uapi/linux/bpf.h | 1 +
>  4 files changed, 11 insertions(+)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 581b2a2e78eb..c0646eceffa2 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1897,6 +1897,7 @@ struct sk_reuseport_kern {
>  	u32 hash;
>  	u32 reuseport_id;
>  	bool bind_inany;
> +	u64 cookie;
>  };
>  bool bpf_tcp_sock_is_valid_access(int off, int size, enum bpf_access_type type,
>  				  struct bpf_insn_access_aux *info);
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 162999b12790..3fcddb032838 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -4403,6 +4403,7 @@ struct sk_reuseport_md {
>  	__u32 ip_protocol;	/* IP protocol. e.g. IPPROTO_TCP, IPPROTO_UDP */
>  	__u32 bind_inany;	/* Is sock bound to an INANY address? */
>  	__u32 hash;		/* A hash of the packet 4 tuples */
> +	__u64 cookie;		/* ID of the listener in map */
Instead of only adding the cookie of a sk, lets make the sk pointer available:

	__bpf_md_ptr(struct bpf_sock *, sk);

and then use the BPF_FUNC_get_socket_cookie to get the cookie.

Other fields of the sk can also be directly accessed too once
the sk pointer is available.