Re: [PATCH mptcp-next v2 3/9] mptcp: add MAPPING_INFINITE mapping status

[Paolo Abeni <pabeni@redhat.com>]

On Thu, 2021-09-09 at 19:51 +0800, Geliang Tang wrote:
> From: Geliang Tang <geliangtang@xiaomi.com>
> 
> This patch added a new mapping status named MAPPING_INFINITE. If the
> MPTCP_INFINITE_DONE flag is set in get_mapping_status, return this new
> status. And in subflow_check_data_avail, if this status is set, goto the
> 'infinite' lable to fallback.
> 
> Signed-off-by: Geliang Tang <geliangtang@xiaomi.com>
> ---
>  net/mptcp/subflow.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> index 951aafb6021e..ad8efe56eab6 100644
> --- a/net/mptcp/subflow.c
> +++ b/net/mptcp/subflow.c
> @@ -798,6 +798,7 @@ enum mapping_status {
>  	MAPPING_INVALID,
>  	MAPPING_EMPTY,
>  	MAPPING_DATA_FIN,
> +	MAPPING_INFINITE,
>  	MAPPING_DUMMY
>  };
>  
> @@ -938,6 +939,9 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
>  	if (!skb)
>  		return MAPPING_EMPTY;
>  
> +	if (mptcp_check_infinite(ssk))
> +		return MAPPING_INFINITE;
> +
>  	if (mptcp_check_fallback(ssk))
>  		return MAPPING_DUMMY;
>  
> @@ -1121,6 +1125,9 @@ static bool subflow_check_data_avail(struct sock *ssk)
>  
>  		status = get_mapping_status(ssk, msk);
>  		trace_subflow_check_data_avail(status, skb_peek(&ssk->sk_receive_queue));
> +		if (unlikely(status == MAPPING_INFINITE))
> +			goto infinite;
> +
>  		if (unlikely(status == MAPPING_INVALID))
>  			goto fallback;
>  
> @@ -1192,6 +1199,7 @@ static bool subflow_check_data_avail(struct sock *ssk)
>  		return false;
>  	}
>  
> +infinite:
>  	__mptcp_do_fallback(msk);
>  	skb = skb_peek(&ssk->sk_receive_queue);
>  	subflow->map_valid = 1;


It looks like MAPPING_INFINITE has almost the same behavior
of MAPPING_DUMMY.

I think we can avoid the new conditional in get_mapping_status().
Eventually we could do all the error checking after the 'fallback:'
label only if the msk has not fallen back yet:

fallback:
	if (!__mptcp_check_fallback(msk)) {
		/* RFC 8684 section 3.7. */
	        if (subflow->send_mp_fail) {
			...
		if (subflow->mp_join || subflow->fully_established) {
			...
		__mptcp_do_fallback(msk);
	}

	skb = skb_peek(&ssk->sk_receive_queue);
	...
WDYT?