netdev - Re: [PATCH bpf-next 1/2] bpf: Adds support for setting window clamp

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Date:   Tue, 1 Dec 2020 18:14:37 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Prankur gupta <prankgup@...com>
Cc:     bpf@...r.kernel.org, kernel-team@...com, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/2] bpf: Adds support for setting window clamp

On Tue, Dec 01, 2020 at 08:43:56AM -0800, Prankur gupta wrote:
> Adds a new bpf_setsockopt for TCP sockets, TCP_BPF_WINDOW_CLAMP,
> which sets the maximum receiver window size. It will be useful for
> limiting receiver window based on RTT.
> 
> Signed-off-by: Prankur gupta <prankgup@...com>
> ---
>  net/core/filter.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 2ca5eecebacf..8c52ffae7b0c 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4910,6 +4910,19 @@ static int _bpf_setsockopt(struct sock *sk, int level, int optname,
>  				tp->notsent_lowat = val;
>  				sk->sk_write_space(sk);
>  				break;
> +			case TCP_WINDOW_CLAMP:
> +				if (!val) {
> +					if (sk->sk_state != TCP_CLOSE) {
> +						ret = -EINVAL;
> +						break;
> +					}
> +					tp->window_clamp = 0;
> +				} else {
> +					tp->window_clamp =
> +						val < SOCK_MIN_RCVBUF / 2 ?
> +						SOCK_MIN_RCVBUF / 2 : val;
> +				}

May be extract this logic into a helper instead of copy-paste?