Commit a0c1d0ea authored by Christoph Paasch's avatar Christoph Paasch Committed by David S. Miller
Browse files

mptcp: Use 32-bit DATA_ACK when possible 



RFC8684 allows to send 32-bit DATA_ACKs as long as the peer is not
sending 64-bit data-sequence numbers. The 64-bit DSN is only there for
extreme scenarios when a very high throughput subflow is combined with a
long-RTT subflow such that the high-throughput subflow wraps around the
32-bit sequence number space within an RTT of the high-RTT subflow.

It is thus a rare scenario and we should try to use the 32-bit DATA_ACK
instead as long as possible. It allows to reduce the TCP-option overhead
by 4 bytes, thus makes space for an additional SACK-block. It also makes
tcpdumps much easier to read when the DSN and DATA_ACK are both either
32 or 64-bit.

Signed-off-by: default avatarChristoph Paasch <cpaasch@apple.com>
Reviewed-by: default avatarMatthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 9efd6a3c

include/net/mptcp.h

+4 −1
Original line number Diff line number Diff line
@@ -16,7 +16,10 @@ struct seq_file; 


/* MPTCP sk_buff extension data */

struct mptcp_ext {

	union {

		u64	data_ack;

		u32	data_ack32;

	};

	u64		data_seq;

	u32		subflow_seq;

	u16		data_len;

net/mptcp/options.c

+24 −9
Original line number Diff line number Diff line
@@ -516,7 +516,16 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb, 
		return ret;

	}



	if (subflow->use_64bit_ack) {

		ack_size = TCPOLEN_MPTCP_DSS_ACK64;

		opts->ext_copy.data_ack = msk->ack_seq;

		opts->ext_copy.ack64 = 1;

	} else {

		ack_size = TCPOLEN_MPTCP_DSS_ACK32;

		opts->ext_copy.data_ack32 = (uint32_t)(msk->ack_seq);

		opts->ext_copy.ack64 = 0;

	}

	opts->ext_copy.use_ack = 1;



	/* Add kind/length/subtype/flag overhead if mapping is not populated */

	if (dss_size == 0)
@@ -524,10 +533,6 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb, 


	dss_size += ack_size;



	opts->ext_copy.data_ack = msk->ack_seq;

	opts->ext_copy.ack64 = 1;

	opts->ext_copy.use_ack = 1;



	*size = ALIGN(dss_size, 4);

	return true;

}
@@ -986,8 +991,13 @@ mp_capable_done: 
		u8 flags = 0;



		if (mpext->use_ack) {

			flags = MPTCP_DSS_HAS_ACK;

			if (mpext->ack64) {

				len += TCPOLEN_MPTCP_DSS_ACK64;

			flags = MPTCP_DSS_HAS_ACK | MPTCP_DSS_ACK64;

				flags |= MPTCP_DSS_ACK64;

			} else {

				len += TCPOLEN_MPTCP_DSS_ACK32;

			}

		}



		if (mpext->use_map) {
@@ -1004,8 +1014,13 @@ mp_capable_done: 
		*ptr++ = mptcp_option(MPTCPOPT_DSS, len, 0, flags);



		if (mpext->use_ack) {

			if (mpext->ack64) {

				put_unaligned_be64(mpext->data_ack, ptr);

				ptr += 2;

			} else {

				put_unaligned_be32(mpext->data_ack32, ptr);

				ptr += 1;

			}

		}



		if (mpext->use_map) {

net/mptcp/protocol.h

+1 −0
Original line number Diff line number Diff line
@@ -290,6 +290,7 @@ struct mptcp_subflow_context { 
		data_avail : 1,

		rx_eof : 1,

		data_fin_tx_enable : 1,

		use_64bit_ack : 1, /* Set when we received a 64-bit DSN */

		can_ack : 1;	    /* only after processing the remote a key */

	u64	data_fin_tx_seq;

	u32	remote_nonce;

net/mptcp/subflow.c

+2 −0
Original line number Diff line number Diff line
@@ -667,9 +667,11 @@ static enum mapping_status get_mapping_status(struct sock *ssk) 
	if (!mpext->dsn64) {

		map_seq = expand_seq(subflow->map_seq, subflow->map_data_len,

				     mpext->data_seq);

		subflow->use_64bit_ack = 0;

		pr_debug("expanded seq=%llu", subflow->map_seq);

	} else {

		map_seq = mpext->data_seq;

		subflow->use_64bit_ack = 1;

	}



	if (subflow->map_valid) {

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