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Date:   Tue, 12 May 2020 22:41:21 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Jakub Sitnicki <jakub@...udflare.com>
CC:     <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <dccp@...r.kernel.org>, <kernel-team@...udflare.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Gerrit Renker <gerrit@....abdn.ac.uk>,
        Jakub Kicinski <kuba@...nel.org>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Marek Majkowski <marek@...udflare.com>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [PATCH bpf-next v2 02/17] bpf: Introduce SK_LOOKUP program type
 with a dedicated attach point

On Mon, May 11, 2020 at 08:52:03PM +0200, Jakub Sitnicki wrote:

[ ... ]

> +BPF_CALL_3(bpf_sk_lookup_assign, struct bpf_sk_lookup_kern *, ctx,
> +	   struct sock *, sk, u64, flags)
The SK_LOOKUP bpf_prog may have already selected the proper reuseport sk.
It is possible by looking up sk from sock_map.

Thus, it is not always desired to do lookup_reuseport() after sk_assign()
in patch 5.  e.g. reuseport_select_sock() just uses a normal hash if
there is no reuse->prog.

A flag (e.g. "BPF_F_REUSEPORT_SELECT") can be added here to
specifically do the reuseport_select_sock() after sk_assign().
If not set, reuseport_select_sock() should not be called.

> +{
> +	if (unlikely(flags != 0))
> +		return -EINVAL;
> +	if (unlikely(sk_is_refcounted(sk)))
> +		return -ESOCKTNOSUPPORT;
> +
> +	/* Check if socket is suitable for packet L3/L4 protocol */
> +	if (sk->sk_protocol != ctx->protocol)
> +		return -EPROTOTYPE;
> +	if (sk->sk_family != ctx->family &&
> +	    (sk->sk_family == AF_INET || ipv6_only_sock(sk)))
> +		return -EAFNOSUPPORT;
> +
> +	/* Select socket as lookup result */
> +	ctx->selected_sk = sk;
> +	return 0;
> +}
> +

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