Re: [MPTCP] [MPTCP][PATCH mptcp-next 4/6] mptcp: add the DSS checksum sending

[Paolo Abeni <pabeni@redhat.com>]

On Mon, 2021-03-22 at 19:37 +0800, Geliang Tang wrote:
> In mptcp_established_options_dss, use the new function
> mptcp_generate_dss_csum to generate the DSS checksum value.
> 
> In mptcp_write_options, send out DSS with the checksum value.
> 
> Signed-off-by: Geliang Tang <geliangtang@gmail.com>
> ---
>  include/net/mptcp.h  |  1 +
>  net/mptcp/options.c  | 41 ++++++++++++++++++++++++++++++++++++++---
>  net/mptcp/protocol.h |  7 +++++++
>  3 files changed, 46 insertions(+), 3 deletions(-)
> 
> diff --git a/include/net/mptcp.h b/include/net/mptcp.h
> index 36fb6907aa6f..869a6d98a72e 100644
> --- a/include/net/mptcp.h
> +++ b/include/net/mptcp.h
> @@ -32,6 +32,7 @@ struct mptcp_ext {
>  			frozen:1,
>  			reset_transient:1;
>  	u8		reset_reason:4;
> +	u16		csum;
>  };
>  
>  #define MPTCP_RM_IDS_MAX	8
> diff --git a/net/mptcp/options.c b/net/mptcp/options.c
> index bdced173edff..69eb15ef9385 100644
> --- a/net/mptcp/options.c
> +++ b/net/mptcp/options.c
> @@ -521,6 +521,30 @@ static void mptcp_write_data_fin(struct mptcp_subflow_context *subflow,
>  	}
>  }
>  
> +static u16 mptcp_generate_dss_csum(struct sk_buff *skb)
> +{
> +	struct csum_pseudo_header header;
> +	struct mptcp_ext *mpext;
> +	__wsum csum;
> +
> +	if (!skb)
> +		return 0;
> +
> +	mpext = mptcp_get_ext(skb);
> +	if (!mpext || !mpext->use_map)
> +		return 0;
> +
> +	header.data_seq = mpext->data_seq;
> +	header.subflow_seq = mpext->subflow_seq;
> +	header.data_len = mpext->data_len;
> +	header.csum = 0;
> +
> +	csum = skb_checksum(skb, 0, skb->len, 0);
> +	csum = csum_partial(&header, sizeof(header), csum);
> +
> +	return csum_fold(csum);
> +}
> +
>  static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
>  					  bool snd_data_fin_enable,
>  					  unsigned int *size,
> @@ -544,8 +568,11 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
>  
>  		remaining -= map_size;
>  		dss_size = map_size;
> -		if (mpext)
> +		if (mpext) {
> +			if (msk->csum_reqd)
> +				mpext->csum = mptcp_generate_dss_csum(skb);
>  			opts->ext_copy = *mpext;
> +		}
>  
>  		if (skb && snd_data_fin_enable)
>  			mptcp_write_data_fin(subflow, skb, &opts->ext_copy);
> @@ -1304,6 +1331,9 @@ void mptcp_write_options(__be32 *ptr, const struct tcp_sock *tp,
>  			flags |= MPTCP_DSS_HAS_MAP | MPTCP_DSS_DSN64;
>  			if (mpext->data_fin)
>  				flags |= MPTCP_DSS_DATA_FIN;
> +
> +			if (mpext->csum)
> +				len += TCPOLEN_MPTCP_DSS_CHECKSUM;
>  		}
>  
>  		*ptr++ = mptcp_option(MPTCPOPT_DSS, len, 0, flags);

If csum is enabled, we additionally need to insert the csum even in the
MPC+data packets.

In a similar way, we need to extract the csum value from MPC+data
packets in the input path, when csum is enabled (in the next patch)

/P