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Date:   Tue, 19 Feb 2019 11:24:10 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     brakmo <brakmo@...com>, netdev <netdev@...r.kernel.org>
Cc:     Martin Lau <kafai@...com>, Alexei Starovoitov <ast@...com>,
        Daniel Borkmann --cc=Kernel Team 
        <"daniel@...earbox.netKernel-team"@fb.com>
Subject: Re: [PATCH bpf-next 1/9] bpf: Add bpf helper bpf_tcp_enter_cwr

On 02/19/2019 06:38 AM, brakmo wrote:
> This patch adds a new bpf helper BPF_FUNC_tcp_enter_cwr
> "int bpf_tcp_enter_cwr(struct bpf_tcp_sock *tp)".
> It is added to BPF_PROG_TYPE_CGROUP_SKB typed bpf_prog
> which currently can be attached to the ingress and egress
> path.
> 
> This helper makes a tcp_sock enter CWR state.  It can be used
> by a bpf_prog to manage egress network bandwidth limit per
> cgroupv2.  A later patch will have a sample program to
> show how it can be used to limit bandwidth usage per cgroupv2.
> 
> Signed-off-by: Lawrence Brakmo <brakmo@...com>
> Signed-off-by: Martin KaFai Lau <kafai@...com>
> ---
>  include/linux/bpf.h      |  1 +
>  include/uapi/linux/bpf.h |  9 ++++++++-
>  kernel/bpf/verifier.c    |  4 ++++
>  net/core/filter.c        | 14 ++++++++++++++
>  4 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index de18227b3d95..525628c913c9 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -195,6 +195,7 @@ enum bpf_arg_type {
>  	ARG_PTR_TO_SOCKET,	/* pointer to bpf_sock */
>  	ARG_PTR_TO_SPIN_LOCK,	/* pointer to bpf_spin_lock */
>  	ARG_PTR_TO_SOCK_COMMON,	/* pointer to sock_common */
> +	ARG_PTR_TO_TCP_SOCK,    /* pointer to tcp_sock */
>  };
>  
>  /* type of values returned from helper functions */
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index bcdd2474eee7..9e9f4f1a0370 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2359,6 +2359,12 @@ union bpf_attr {
>   *	Return
>   *		A **struct bpf_tcp_sock** pointer on success, or NULL in
>   *		case of failure.
> + *
> + * int bpf_tcp_enter_cwr(struct bpf_tcp_sock *tp)
> + *    Description
> + *        Make a tcp_sock enter CWR state.
> + *    Return
> + *        0
>   */
>  #define __BPF_FUNC_MAPPER(FN)		\
>  	FN(unspec),			\
> @@ -2457,7 +2463,8 @@ union bpf_attr {
>  	FN(spin_lock),			\
>  	FN(spin_unlock),		\
>  	FN(sk_fullsock),		\
> -	FN(tcp_sock),
> +	FN(tcp_sock),			\
> +	FN(tcp_enter_cwr),
>  
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>   * function eBPF program intends to call
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 1b9496c41383..95fb385c6f3c 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2424,6 +2424,10 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
>  			return -EFAULT;
>  		}
>  		meta->ptr_id = reg->id;
> +	} else if (arg_type == ARG_PTR_TO_TCP_SOCK) {
> +		expected_type = PTR_TO_TCP_SOCK;
> +		if (type != expected_type)
> +			goto err_type;
>  	} else if (arg_type == ARG_PTR_TO_SPIN_LOCK) {
>  		if (meta->func_id == BPF_FUNC_spin_lock) {
>  			if (process_spin_lock(env, regno, true))
> diff --git a/net/core/filter.c b/net/core/filter.c
> index b584cb42a803..f51c4a781844 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -5426,6 +5426,18 @@ static const struct bpf_func_proto bpf_tcp_sock_proto = {
>  	.arg1_type	= ARG_PTR_TO_SOCK_COMMON,
>  };
>  
> +BPF_CALL_1(bpf_tcp_enter_cwr, struct tcp_sock *, tp)
> +{
> +	tcp_enter_cwr((struct sock *)tp);

Is it safe to call in every case, meaning do we always have a icsk_ca_ops
assigned (e.g. pre-4whs completion)?

> +	return 0;
> +}
> +
> +static const struct bpf_func_proto bpf_tcp_enter_cwr_proto = {
> +	.func        = bpf_tcp_enter_cwr,
> +	.gpl_only    = false,
> +	.ret_type    = RET_INTEGER,
> +	.arg1_type    = ARG_PTR_TO_TCP_SOCK,
> +};
>  #endif /* CONFIG_INET */
>  
>  bool bpf_helper_changes_pkt_data(void *func)
> @@ -5585,6 +5597,8 @@ cg_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  #ifdef CONFIG_INET
>  	case BPF_FUNC_tcp_sock:
>  		return &bpf_tcp_sock_proto;
> +	case BPF_FUNC_tcp_enter_cwr:
> +		return &bpf_tcp_enter_cwr_proto;
>  #endif
>  	default:
>  		return sk_filter_func_proto(func_id, prog);
> 

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