netdev - Re: [PATCH net-next 2/3] bpf: Add new cgroups prog type to enable sock modifications

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Date:   Wed, 26 Oct 2016 10:08:33 -0600
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Thomas Graf <tgraf@...g.ch>
Cc:     netdev@...r.kernel.org, daniel@...que.org, ast@...com,
        daniel@...earbox.net
Subject: Re: [PATCH net-next 2/3] bpf: Add new cgroups prog type to enable
 sock modifications

On 10/26/16 2:41 AM, Thomas Graf wrote:
> On 10/25/16 at 03:30pm, David Ahern wrote:
>> @@ -171,6 +177,9 @@ int __cgroup_bpf_run_filter(struct sock *sk,
>>  		case BPF_CGROUP_INET_EGRESS:
>>  			ret = __cgroup_bpf_run_filter_skb(skb, prog);
>>  			break;
>> +		case BPF_CGROUP_INET_SOCK_CREATE:
>> +			ret = __cgroup_bpf_run_filter_sk_create(sk, prog);
>> +			break;
>>  		/* make gcc happy else complains about missing enum value */
>>  		default:
>>  			return 0;
> 
> Thinking further ahead of your simple example. Instead of adding yet
> another prog type for the same hook, we can make this compatible with
> BPF_CGROUP_INET_EGRESS instead which would then provide a ctx which
> contains both, the sk and skb.
> 
> The ctx concept is very flexible. We can keep the existing dummy skb
> representation and add sk_ fields which are only valid for BPF at
> socket layer, e.g skb->sk_bound_dev_if would translate to
> sk->bound_dev_if.
> 

It's an odd user semantic to me to put sock elements into the shadow sk_buff and to reuse BPF_CGROUP_INET_EGRESS. 

I can drop the _CREATE and just make it BPF_CGROUP_INET_SOCK so it works for any sock modification someone wants to add -- e.g., the port binding use case.