netdev - Re: [bpf-next RFC 1/3] flow_dissector: implements flow dissector BPF hook

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Date:   Thu, 16 Aug 2018 19:34:12 +0100
From:   Edward Cree <ecree@...arflare.com>
To:     Petar Penkov <peterpenkov96@...il.com>, <netdev@...r.kernel.org>
CC:     <davem@...emloft.net>, <ast@...nel.org>, <daniel@...earbox.net>,
        <simon.horman@...ronome.com>, Petar Penkov <ppenkov@...gle.com>,
        "Willem de Bruijn" <willemb@...gle.com>
Subject: Re: [bpf-next RFC 1/3] flow_dissector: implements flow dissector BPF
 hook

On 16/08/18 17:44, Petar Penkov wrote:
> From: Petar Penkov <ppenkov@...gle.com>
>
> Adds a hook for programs of type BPF_PROG_TYPE_FLOW_DISSECTOR and
> attach type BPF_FLOW_DISSECTOR that is executed in the flow dissector
> path. The BPF program is kept as a global variable so it is
> accessible to all flow dissectors.
>
> Signed-off-by: Petar Penkov <ppenkov@...gle.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> ---

This looks really great.

> +int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr)
> +{
> +	struct bpf_prog *attached;
> +
> +	mutex_lock(&flow_dissector_mutex);
> +	attached = rcu_dereference_protected(flow_dissector_prog,
> +					     lockdep_is_held(&flow_dissector_mutex));
> +	if (!flow_dissector_prog) {
> +		mutex_unlock(&flow_dissector_mutex);
> +		return -EINVAL;
Wouldn't -ENOENT be more usual here (as the counterpart to -EEXIST in
 the skb_flow_dissector_bpf_prog_attach() version just above)?

-Ed