netdev - Re: [PATCH bpf-next 07/11] bpf: Add helper to retrieve socket in BPF

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Date:   Wed, 12 Sep 2018 17:06:31 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Joe Stringer <joe@...d.net.nz>
Cc:     daniel@...earbox.net, netdev@...r.kernel.org, ast@...nel.org,
        john.fastabend@...il.com, tgraf@...g.ch, kafai@...com,
        nitin.hande@...il.com, mauricio.vasquez@...ito.it
Subject: Re: [PATCH bpf-next 07/11] bpf: Add helper to retrieve socket in BPF

On Tue, Sep 11, 2018 at 05:36:36PM -0700, Joe Stringer wrote:
> This patch adds new BPF helper functions, bpf_sk_lookup_tcp() and
> bpf_sk_lookup_udp() which allows BPF programs to find out if there is a
> socket listening on this host, and returns a socket pointer which the
> BPF program can then access to determine, for instance, whether to
> forward or drop traffic. bpf_sk_lookup_xxx() may take a reference on the
> socket, so when a BPF program makes use of this function, it must
> subsequently pass the returned pointer into the newly added sk_release()
> to return the reference.
> 
> By way of example, the following pseudocode would filter inbound
> connections at XDP if there is no corresponding service listening for
> the traffic:
> 
>   struct bpf_sock_tuple tuple;
>   struct bpf_sock_ops *sk;
> 
>   populate_tuple(ctx, &tuple); // Extract the 5tuple from the packet
>   sk = bpf_sk_lookup_tcp(ctx, &tuple, sizeof tuple, netns, 0);
...
> +struct bpf_sock_tuple {
> +	union {
> +		__be32 ipv6[4];
> +		__be32 ipv4;
> +	} saddr;
> +	union {
> +		__be32 ipv6[4];
> +		__be32 ipv4;
> +	} daddr;
> +	__be16 sport;
> +	__be16 dport;
> +	__u8 family;
> +};

since we can pass ptr_to_packet into map lookup and other helpers now,
can you move 'family' out of bpf_sock_tuple and combine with netns_id arg?
then progs wouldn't need to copy bytes from the packet into tuple
to do a lookup.
The rest looks great to me.