Re: [PATCH bpf-next] bpf: add sock_ops callbacks for data send/recv/acked events

[Philo Lu <lulie@linux.alibaba.com>]

Sorry, I forgot to cc the maintainers.

On 2023/11/23 11:07, Philo Lu wrote:
> Add 3 sock_ops operators, namely BPF_SOCK_OPS_DATA_SEND_CB,
> BPF_SOCK_OPS_DATA_RECV_CB, and BPF_SOCK_OPS_DATA_ACKED_CB. A flag
> BPF_SOCK_OPS_DATA_EVENT_CB_FLAG is provided to minimize the performance
> impact. The flag must be explicitly set to enable these callbacks.
>
> If the flag is enabled, bpf sock_ops program will be called every time a
> tcp data packet is sent, received, and acked.
> BPF_SOCK_OPS_DATA_SEND_CB: call bpf after a data packet is sent.
> BPF_SOCK_OPS_DATA_RECV_CB: call bpf after a data packet is receviced.
> BPF_SOCK_OPS_DATA_ACKED_CB: call bpf after a valid ack packet is
> processed (some sent data are ackknowledged).
>
> We use these callbacks for fine-grained tcp monitoring, which collects
> and analyses every tcp request/response event information. The whole
> system has been described in SIGMOD'18 (see
> https://dl.acm.org/doi/pdf/10.1145/3183713.3190659 for details). To
> achieve this with bpf, we require hooks for data events that call
> sock_ops bpf (1) when any data packet is sent/received/acked, and (2)
> after critical tcp state variables have been updated (e.g., snd_una,
> snd_nxt, rcv_nxt). However, existing sock_ops operators cannot meet our
> requirements.
>
> Besides, these hooks also help to debug tcp when data send/recv/acked.
>
> Signed-off-by: Philo Lu <lulie@linux.alibaba.com>
> ---
>   include/net/tcp.h        |  9 +++++++++
>   include/uapi/linux/bpf.h | 14 +++++++++++++-
>   net/ipv4/tcp_input.c     |  4 ++++
>   net/ipv4/tcp_output.c    |  2 ++
>   4 files changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index d2f0736b76b8..73eda03fdda5 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -2660,6 +2660,15 @@ static inline void tcp_bpf_rtt(struct sock *sk)
>   		tcp_call_bpf(sk, BPF_SOCK_OPS_RTT_CB, 0, NULL);
>   }
>   
> +/* op must be one of BPF_SOCK_OPS_DATA_SEND_CB, BPF_SOCK_OPS_DATA_RECV_CB,
> + * or BPF_SOCK_OPS_DATA_ACKED_CB.
> + */
> +static inline void tcp_bpf_data_event(struct sock *sk, int op)
> +{
> +	if (BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk), BPF_SOCK_OPS_DATA_EVENT_CB_FLAG))
> +		tcp_call_bpf(sk, op, 0, NULL);
> +}
> +
>   #if IS_ENABLED(CONFIG_SMC)
>   extern struct static_key_false tcp_have_smc;
>   #endif
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 7cf8bcf9f6a2..2154a6235901 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3016,6 +3016,7 @@ union bpf_attr {
>    * 		* **BPF_SOCK_OPS_RETRANS_CB_FLAG** (retransmission)
>    * 		* **BPF_SOCK_OPS_STATE_CB_FLAG** (TCP state change)
>    * 		* **BPF_SOCK_OPS_RTT_CB_FLAG** (every RTT)
> + * 		* **BPF_SOCK_OPS_DATA_EVENT_CB_FLAG** (data packet send/recv/acked)
>    *
>    * 		Therefore, this function can be used to clear a callback flag by
>    * 		setting the appropriate bit to zero. e.g. to disable the RTO
> @@ -6755,8 +6756,10 @@ enum {
>   	 * options first before the BPF program does.
>   	 */
>   	BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG = (1<<6),
> +	/* Call bpf when data send/recv/acked. */
> +	BPF_SOCK_OPS_DATA_EVENT_CB_FLAG = (1<<7),
>   /* Mask of all currently supported cb flags */
> -	BPF_SOCK_OPS_ALL_CB_FLAGS       = 0x7F,
> +	BPF_SOCK_OPS_ALL_CB_FLAGS       = 0xFF,
>   };
>   
>   /* List of known BPF sock_ops operators.
> @@ -6869,6 +6872,15 @@ enum {
>   					 * by the kernel or the
>   					 * earlier bpf-progs.
>   					 */
> +	BPF_SOCK_OPS_DATA_SEND_CB,		/* Calls BPF program when a
> +					 * data packet is sent. Pure ack is ignored.
> +					 */
> +	BPF_SOCK_OPS_DATA_RECV_CB,		/* Calls BPF program when a
> +					 * data packet is received. Pure ack is ignored.
> +					 */
> +	BPF_SOCK_OPS_DATA_ACKED_CB,		/* Calls BPF program when sent
> +					 * data are acknowledged.
> +					 */
>   };
>   
>   /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index bcb55d98004c..72c6192e7cd0 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -824,6 +824,8 @@ static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
>   
>   	now = tcp_jiffies32;
>   
> +	tcp_bpf_data_event(sk, BPF_SOCK_OPS_DATA_RECV_CB);
> +
>   	if (!icsk->icsk_ack.ato) {
>   		/* The _first_ data packet received, initialize
>   		 * delayed ACK engine.
> @@ -3454,6 +3456,8 @@ static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb,
>   		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
>   	}
>   
> +	tcp_bpf_data_event(sk, BPF_SOCK_OPS_DATA_ACKED_CB);
> +
>   	if (icsk->icsk_ca_ops->pkts_acked) {
>   		struct ack_sample sample = { .pkts_acked = pkts_acked,
>   					     .rtt_us = sack->rate->rtt_us };
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index eb13a55d660c..ddd6a9c2150f 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -2821,6 +2821,8 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
>   		/* Send one loss probe per tail loss episode. */
>   		if (push_one != 2)
>   			tcp_schedule_loss_probe(sk, false);
> +
> +		tcp_bpf_data_event(sk, BPF_SOCK_OPS_DATA_SEND_CB);
>   		return false;
>   	}
>   	return !tp->packets_out && !tcp_write_queue_empty(sk);