mptcp: Write MPTCP DSS headers to outgoing data packets

Per-packet metadata required to write the MPTCP DSS option is written to
the skb_ext area. One write to the socket may contain more than one
packet of data, which is copied to page fragments and mapped in to MPTCP
DSS segments with size determined by the available page fragments and
the maximum mapping length allowed by the MPTCP specification. If
do_tcp_sendpages() splits a DSS segment in to multiple skbs, that's ok -
the later skbs can either have duplicated DSS mapping information or
none at all, and the receiver can handle that.

The current implementation uses the subflow frag cache and tcp
sendpages to avoid excessive code duplication. More work is required to
ensure that it works correctly under memory pressure and to support
MPTCP-level retransmissions.

The MPTCP DSS checksum is not yet implemented.

Co-developed-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Co-developed-by: Peter Krystad <peter.krystad@linux.intel.com>
Signed-off-by: Peter Krystad <peter.krystad@linux.intel.com>
Co-developed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 0 deletions

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 5f43fa0275c0..384ec4804198 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -32,6 +32,10 @@
 #define TCPOLEN_MPTCP_MPC_SYN		12
 #define TCPOLEN_MPTCP_MPC_SYNACK	12
 #define TCPOLEN_MPTCP_MPC_ACK		20
+#define TCPOLEN_MPTCP_DSS_BASE		4
+#define TCPOLEN_MPTCP_DSS_ACK64		8
+#define TCPOLEN_MPTCP_DSS_MAP64		14
+#define TCPOLEN_MPTCP_DSS_CHECKSUM	2
 
 /* MPTCP MP_CAPABLE flags */
 #define MPTCP_VERSION_MASK	(0x0F)
@@ -40,14 +44,24 @@
 #define MPTCP_CAP_HMAC_SHA1	BIT(0)
 #define MPTCP_CAP_FLAG_MASK	(0x3F)
 
+/* MPTCP DSS flags */
+#define MPTCP_DSS_DATA_FIN	BIT(4)
+#define MPTCP_DSS_DSN64		BIT(3)
+#define MPTCP_DSS_HAS_MAP	BIT(2)
+#define MPTCP_DSS_ACK64		BIT(1)
+#define MPTCP_DSS_HAS_ACK	BIT(0)
+
 /* MPTCP connection sock */
 struct mptcp_sock {
 	/* inet_connection_sock must be the first member */
 	struct inet_connection_sock sk;
 	u64		local_key;
 	u64		remote_key;
+	u64		write_seq;
+	u64		ack_seq;
 	u32		token;
 	struct list_head conn_list;
+	struct skb_ext	*cached_ext;	/* for the next sendmsg */
 	struct socket	*subflow; /* outgoing connect/listener/!mp_capable */
 };
 
@@ -83,6 +97,7 @@ struct mptcp_subflow_context {
 	u64	remote_key;
 	u64	idsn;
 	u32	token;
+	u32	rel_write_seq;
 	u32	request_mptcp : 1,  /* send MP_CAPABLE */
 		mp_capable : 1,	    /* remote is MPTCP capable */
 		fourth_ack : 1,	    /* send initial DSS */
@@ -144,4 +159,9 @@ static inline void mptcp_crypto_key_gen_sha(u64 *key, u32 *token, u64 *idsn)
 void mptcp_crypto_hmac_sha(u64 key1, u64 key2, u32 nonce1, u32 nonce2,
 			   u32 *hash_out);
 
+static inline struct mptcp_ext *mptcp_get_ext(struct sk_buff *skb)
+{
+	return (struct mptcp_ext *)skb_ext_find(skb, SKB_EXT_MPTCP);
+}
+
 #endif /* __MPTCP_PROTOCOL_H */