netdev - Re: [PATCH bpf-next v2 1/2] bpf: Allow bpf_get_netns_cookie in BPF_PROG_TYPE_CGROUP

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Date:   Fri, 13 Aug 2021 12:58:02 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Stanislav Fomichev <sdf@...gle.com>
CC:     <netdev@...r.kernel.org>, <bpf@...r.kernel.org>, <ast@...nel.org>,
        <daniel@...earbox.net>, <andrii@...nel.org>
Subject: Re: [PATCH bpf-next v2 1/2] bpf: Allow bpf_get_netns_cookie in
 BPF_PROG_TYPE_CGROUP_SOCKOPT

On Thu, Aug 12, 2021 at 08:30:10AM -0700, Stanislav Fomichev wrote:
> This is similar to existing BPF_PROG_TYPE_CGROUP_SOCK
> and BPF_PROG_TYPE_CGROUP_SOCK_ADDR.
> 
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
>  kernel/bpf/cgroup.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index b567ca46555c..ca5af8852260 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -1846,11 +1846,30 @@ const struct bpf_verifier_ops cg_sysctl_verifier_ops = {
>  const struct bpf_prog_ops cg_sysctl_prog_ops = {
>  };
>  
> +#ifdef CONFIG_NET
> +BPF_CALL_1(bpf_get_netns_cookie_sockopt, struct bpf_sockopt_kern *, ctx)
> +{
> +	struct sock *sk = ctx ? ctx->sk : NULL;
> +	const struct net *net = sk ? sock_net(sk) : &init_net;
A nit.

ctx->sk can not be NULL here, so it only depends on ctx is NULL or not.

If I read it correctly, would it be less convoluted to directly test ctx
and use ctx->sk here, like:

	const struct net *net = ctx ? sock_net(ctx->sk) : &init_net;

and the previous "struct sock *sk = ctx ? ctx->sk : NULL;" statement
can also be removed.

> +
> +	return net->net_cookie;
> +}
> +