Re: [MPTCP] [RFC PATCH v4 08/17] mptcp: Create SUBFLOW socket for incoming connections

[Krystad, Peter <peter.krystad at intel.com>]

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On Tue, 2018-12-11 at 22:08 -0800, Christoph Paasch wrote:
> Hello,
> 
> On 30/11/18 - 12:11:03, Mat Martineau wrote:
> > From: Peter Krystad <peter.krystad(a)intel.com>
> > 
> > Add subflow_request_sock type that extends tcp_request_sock
> > and add an is_mptcp flag to tcp_request_sock distinguish them.
> > 
> > Override the listen() and accept() methods of the MPTCP
> > socket proto_ops so they may act on the subflow socket.
> > 
> > Override the conn_request() and syn_recv_sock() handlers
> > in the inet_connection_sock to handle incoming MPTCP
> > SYNs and the ACK to the response SYN.
> 
> I'm having quite a hard time to understand how it works. Can you give some
> more details?
> 
> Because, the difficult part about MPTCP is that incoming subflows are no
> more matching on a listener but rather on a "established" MPTCP-socket based
> on the token that is present in the TCP-options.
> And, I don't see how this is being taken care of here.
> 
> Is the expectation that the app will call "listen()" and "accept()" on the
> MPTCP-socket ?

Yes, the application will call listen() and accept() with the socket it
got when it called socket(..., IPPROTO_MPTCP), the normal call sequence
for a server application is preserved. In the kernel this socket is
represented by struct mptcp_sock.

Key generation and token-tracking data structure is added in the next
patch, #9.

How this works is that underneath the MPTCP socket is a subflow socket
that is a struct subflow_sock. This is an extended tcp_sock structure
with subflow-specific fields. mptcp_stream_listen() and
mptcp_stream_accept() routines in this patch call inet_listen() and
inet_accept() on the subflow socket just like it were a listening TCP
socket.

When an initial MPTCP connection completes on the subflow_socket
mptcp_accept() creates a new mptcp_sock, attaches the child tcp_sock
(returned by kernel_accept()) to it and this new MPTCP socket is
returned to the application. In patch #9 you can see the token and new
mptcp_sock are stored in the token tree, so we can find it when
additional subflows are created.

Let me know if you have more questions.

Peter.


> Thanks,
> Christoph
> 
> > 
> > Add handling in tcp_output.c to add MP_CAPABLE to an outgoing
> > SYN-ACK response for a subflow_request_sock.
> > 
> > Signed-off-by: Peter Krystad <peter.krystad(a)intel.com>
> > ---
> >  include/linux/tcp.h   |   1 +
> >  include/net/mptcp.h   |  26 ++++++++++
> >  include/net/tcp.h     |   1 +
> >  net/ipv4/tcp_input.c  |   1 +
> >  net/ipv4/tcp_output.c |  21 +++++++-
> >  net/mptcp/options.c   |  15 ++++++
> >  net/mptcp/protocol.c  | 102 ++++++++++++++++++++++++++++++++++---
> >  net/mptcp/subflow.c   | 115 ++++++++++++++++++++++++++++++++++++++++--
> >  8 files changed, 271 insertions(+), 11 deletions(-)
> > 
> > diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> > index 2622817ecd6b..b54ab3b5546a 100644
> > --- a/include/linux/tcp.h
> > +++ b/include/linux/tcp.h
> > @@ -148,6 +148,7 @@ struct tcp_request_sock {
> >  						  * FastOpen it's the seq#
> >  						  * after data-in-SYN.
> >  						  */
> > +	bool				is_mptcp;
> >  };
> >  
> >  static inline struct tcp_request_sock *tcp_rsk(const struct request_sock *req)
> > diff --git a/include/net/mptcp.h b/include/net/mptcp.h
> > index a5c2baeb688f..ced33f1c529e 100644
> > --- a/include/net/mptcp.h
> > +++ b/include/net/mptcp.h
> > @@ -69,6 +69,23 @@ static inline struct subflow_sock *subflow_sk(const struct sock *sk)
> >  	return (struct subflow_sock *)sk;
> >  }
> >  
> > +struct subflow_request_sock {
> > +	struct	tcp_request_sock sk;
> > +	u8	mp_capable : 1,
> > +		mp_join : 1,
> > +		checksum : 1,
> > +		backup : 1,
> > +		version : 4;
> > +	u64	local_key;
> > +	u64	remote_key;
> > +};
> > +
> > +static inline
> > +struct subflow_request_sock *subflow_rsk(const struct request_sock *rsk)
> > +{
> > +	return (struct subflow_request_sock *)rsk;
> > +}
> > +
> >  #ifdef CONFIG_MPTCP
> >  
> >  void mptcp_parse_option(const unsigned char *ptr, int opsize,
> > @@ -77,6 +94,8 @@ unsigned int mptcp_syn_options(struct sock *sk, u64 *local_key);
> >  void mptcp_rcv_synsent(struct sock *sk);
> >  unsigned int mptcp_established_options(struct sock *sk, u64 *local_key,
> >  				       u64 *remote_key);
> > +unsigned int mptcp_synack_options(struct request_sock *req,
> > +				  u64 *local_key, u64 *remote_key);
> >  
> >  void mptcp_finish_connect(struct sock *sk, int mp_capable);
> >  
> > @@ -104,6 +123,13 @@ static inline void mptcp_rcv_synsent(struct sock *sk)
> >  {
> >  }
> >  
> > +static inline unsigned int mptcp_synack_options(struct request_sock *sk,
> > +						u64 *local_key,
> > +						u64 *remote_key)
> > +{
> > +	return 0;
> > +}
> > +
> >  static inline unsigned int mptcp_established_options(struct sock *sk,
> >  						     u64 *local_key,
> >  						     u64 *remote_key)
> > diff --git a/include/net/tcp.h b/include/net/tcp.h
> > index 254cf82e2ec6..1fc6362fa778 100644
> > --- a/include/net/tcp.h
> > +++ b/include/net/tcp.h
> > @@ -216,6 +216,7 @@ void tcp_time_wait(struct sock *sk, int state, int timeo);
> >  #define TCPOLEN_MSS_ALIGNED		4
> >  #define TCPOLEN_EXP_SMC_BASE_ALIGNED	8
> >  #define TCPOLEN_MPTCP_MPC_SYN		12
> > +#define TCPOLEN_MPTCP_MPC_SYNACK	20
> >  #define TCPOLEN_MPTCP_MPC_ACK		20
> >  
> >  /* Flags in tp->nonagle */
> > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> > index eda515b141fb..00f7a3d88d66 100644
> > --- a/net/ipv4/tcp_input.c
> > +++ b/net/ipv4/tcp_input.c
> > @@ -6445,6 +6445,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
> >  
> >  	tcp_rsk(req)->af_specific = af_ops;
> >  	tcp_rsk(req)->ts_off = 0;
> > +	tcp_rsk(req)->is_mptcp = 0;
> >  
> >  	tcp_clear_options(&tmp_opt);
> >  	tmp_opt.mss_clamp = af_ops->mss_clamp;
> > diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> > index 4f284ed879ba..6f723cdb5c8e 100644
> > --- a/net/ipv4/tcp_output.c
> > +++ b/net/ipv4/tcp_output.c
> > @@ -416,6 +416,7 @@ static inline bool tcp_urg_mode(const struct tcp_sock *tp)
> >  
> >  /* MPTCP option subtypes */
> >  #define OPTION_MPTCP_MPC_SYN	(1 << 0)
> > +#define OPTION_MPTCP_MPC_SYNACK	(1 << 1)
> >  #define OPTION_MPTCP_MPC_ACK	(1 << 2)
> >  
> >  struct tcp_out_options {
> > @@ -439,12 +440,15 @@ static void mptcp_options_write(__be32 *ptr, struct tcp_out_options *opts)
> >  		return;
> >  
> >  	if ((OPTION_MPTCP_MPC_SYN |
> > +	     OPTION_MPTCP_MPC_SYNACK |
> >  	     OPTION_MPTCP_MPC_ACK) & opts->suboptions) {
> >  		u8 len;
> >  		__be64 key;
> >  
> >  		if (OPTION_MPTCP_MPC_SYN & opts->suboptions)
> >  			len = TCPOLEN_MPTCP_MPC_SYN;
> > +		else if (OPTION_MPTCP_MPC_SYNACK & opts->suboptions)
> > +			len = TCPOLEN_MPTCP_MPC_SYNACK;
> >  		else
> >  			len = TCPOLEN_MPTCP_MPC_ACK;
> >  
> > @@ -455,7 +459,8 @@ static void mptcp_options_write(__be32 *ptr, struct tcp_out_options *opts)
> >  		key = cpu_to_be64(opts->sndr_key);
> >  		memcpy((u8 *) ptr, (u8 *) &key, 8);
> >  		ptr += 2;
> > -		if (OPTION_MPTCP_MPC_ACK & opts->suboptions) {
> > +		if ((OPTION_MPTCP_MPC_SYNACK |
> > +		     OPTION_MPTCP_MPC_ACK) & opts->suboptions) {
> >  			key = cpu_to_be64(opts->rcvr_key);
> >  			memcpy((u8 *) ptr, (u8 *) &key, 8);
> >  			ptr += 2;
> > @@ -762,6 +767,20 @@ static unsigned int tcp_synack_options(const struct sock *sk,
> >  			remaining -= need;
> >  		}
> >  	}
> > +	if (tcp_rsk(req)->is_mptcp) {
> > +		u64 local_key;
> > +		u64 remote_key;
> > +		if (mptcp_synack_options(req, &local_key, &remote_key)) {
> > +			if (remaining >= TCPOLEN_MPTCP_MPC_SYNACK) {
> > +				opts->options |= OPTION_MPTCP;
> > +				opts->suboptions = OPTION_MPTCP_MPC_SYNACK;
> > +				opts->sndr_key = local_key;
> > +				opts->rcvr_key = remote_key;
> > +				remaining -= TCPOLEN_MPTCP_MPC_SYNACK;
> > +			}
> > +		}
> > +	}
> > +
> >  	smc_set_option_cond(tcp_sk(sk), ireq, opts, &remaining);
> >  
> >  	return MAX_TCP_OPTION_SPACE - remaining;
> > diff --git a/net/mptcp/options.c b/net/mptcp/options.c
> > index b0616f520da0..266a9f7fed0d 100644
> > --- a/net/mptcp/options.c
> > +++ b/net/mptcp/options.c
> > @@ -189,3 +189,18 @@ unsigned int mptcp_established_options(struct sock *sk, u64 *local_key,
> >  	}
> >  	return 0;
> >  }
> > +
> > +unsigned int mptcp_synack_options(struct request_sock *req, u64 *local_key,
> > +				  u64 *remote_key)
> > +{
> > +	struct subflow_request_sock *subflow_req = subflow_rsk(req);
> > +
> > +	pr_debug("subflow_req=%p", subflow_req);
> > +	if (subflow_req->mp_capable) {
> > +		*local_key = subflow_req->local_key;
> > +		*remote_key = subflow_req->remote_key;
> > +		pr_debug("local_key=%llu", *local_key);
> > +		pr_debug("remote_key=%llu", *remote_key);
> > +	}
> > +	return subflow_req->mp_capable;
> > +}
> > diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> > index 1a3412a742ea..9f802f69a528 100644
> > --- a/net/mptcp/protocol.c
> > +++ b/net/mptcp/protocol.c
> > @@ -80,6 +80,45 @@ static void mptcp_close(struct sock *sk, long timeout)
> >  	}
> >  }
> >  
> > +static struct sock *mptcp_accept(struct sock *sk, int flags, int *err,
> > +				 bool kern)
> > +{
> > +	struct mptcp_sock *msk = mptcp_sk(sk);
> > +	struct socket *listener = msk->subflow;
> > +	struct socket *new_sock;
> > +	struct socket *mp;
> > +	struct subflow_sock *subflow;
> > +
> > +	pr_debug("msk=%p, listener=%p", msk, listener->sk);
> > +	*err = kernel_accept(listener, &new_sock, flags);
> > +	if (*err < 0)
> > +		return NULL;
> > +
> > +	subflow = subflow_sk(new_sock->sk);
> > +	pr_debug("new_sock=%p", subflow);
> > +
> > +	*err = sock_create(PF_INET, SOCK_STREAM, IPPROTO_MPTCP, &mp);
> > +	if (*err < 0) {
> > +		kernel_sock_shutdown(new_sock, SHUT_RDWR);
> > +		sock_release(new_sock);
> > +		return NULL;
> > +	}
> > +
> > +	msk = mptcp_sk(mp->sk);
> > +	pr_debug("msk=%p", msk);
> > +	subflow->conn = mp->sk;
> > +
> > +	if (subflow->mp_capable) {
> > +		msk->remote_key = subflow->remote_key;
> > +		msk->local_key = subflow->local_key;
> > +		msk->connection_list = new_sock;
> > +	} else {
> > +		msk->subflow = new_sock;
> > +	}
> > +
> > +	return mp->sk;
> > +}
> > +
> >  static int mptcp_get_port(struct sock *sk, unsigned short snum)
> >  {
> >  	struct mptcp_sock *msk = mptcp_sk(sk);
> > @@ -129,11 +168,16 @@ static int subflow_create(struct sock *sock)
> >  int mptcp_stream_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
> >  {
> >  	struct mptcp_sock *msk = mptcp_sk(sock->sk);
> > -	struct socket *subflow = msk->subflow;
> > +	int err;
> >  
> > -	pr_debug("msk=%p, subflow=%p", msk, subflow->sk);
> > +	pr_debug("msk=%p", msk);
> >  
> > -	return inet_bind(subflow, uaddr, addr_len);
> > +	if (msk->subflow == NULL) {
> > +		err = subflow_create(sock->sk);
> > +		if (err)
> > +			return err;
> > +	}
> > +	return inet_bind(msk->subflow, uaddr, addr_len);
> >  }
> >  
> >  int mptcp_stream_connect(struct socket *sock, struct sockaddr *uaddr,
> > @@ -153,12 +197,56 @@ int mptcp_stream_connect(struct socket *sock, struct sockaddr *uaddr,
> >  	return inet_stream_connect(msk->subflow, uaddr, addr_len, flags);
> >  }
> >  
> > +int mptcp_stream_getname(struct socket *sock, struct sockaddr *uaddr, int peer)
> > +{
> > +	struct mptcp_sock *msk = mptcp_sk(sock->sk);
> > +	struct socket *subflow;
> > +	int err = -EPERM;
> > +
> > +	if (msk->connection_list)
> > +		subflow = msk->connection_list;
> > +	else
> > +		subflow = msk->subflow;
> > +
> > +	err = inet_getname(subflow, uaddr, peer);
> > +
> > +	return err;
> > +}
> > +
> > +int mptcp_stream_listen(struct socket *sock, int backlog)
> > +{
> > +	struct mptcp_sock *msk = mptcp_sk(sock->sk);
> > +	int err;
> > +
> > +	pr_debug("msk=%p", msk);
> > +
> > +	if (msk->subflow == NULL) {
> > +		err = subflow_create(sock->sk);
> > +		if (err)
> > +			return err;
> > +	}
> > +	return inet_listen(msk->subflow, backlog);
> > +}
> > +
> > +int mptcp_stream_accept(struct socket *sock, struct socket *newsock, int flags,
> > +			bool kern)
> > +{
> > +	struct mptcp_sock *msk = mptcp_sk(sock->sk);
> > +
> > +	pr_debug("msk=%p", msk);
> > +
> > +	if (msk->subflow == NULL) {
> > +		return -EINVAL;
> > +	}
> > +	return inet_accept(sock, newsock, flags, kern);
> > +}
> > +
> >  static struct proto mptcp_prot = {
> >  	.name		= "MPTCP",
> >  	.owner		= THIS_MODULE,
> >  	.init		= mptcp_init_sock,
> >  	.close		= mptcp_close,
> > -	.accept		= inet_csk_accept,
> > +	.accept		= mptcp_accept,
> >  	.shutdown	= tcp_shutdown,
> >  	.sendmsg	= mptcp_sendmsg,
> >  	.recvmsg	= mptcp_recvmsg,
> > @@ -176,11 +264,11 @@ const struct proto_ops mptcp_stream_ops = {
> >  	.bind		   = mptcp_stream_bind,
> >  	.connect	   = mptcp_stream_connect,
> >  	.socketpair	   = sock_no_socketpair,
> > -	.accept		   = inet_accept,
> > -	.getname	   = inet_getname,
> > +	.accept		   = mptcp_stream_accept,
> > +	.getname	   = mptcp_stream_getname,
> >  	.poll		   = tcp_poll,
> >  	.ioctl		   = inet_ioctl,
> > -	.listen		   = inet_listen,
> > +	.listen		   = mptcp_stream_listen,
> >  	.shutdown	   = inet_shutdown,
> >  	.setsockopt	   = sock_common_setsockopt,
> >  	.getsockopt	   = sock_common_getsockopt,
> > diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> > index 5e5fdcb3175f..89fcc3b746eb 100644
> > --- a/net/mptcp/subflow.c
> > +++ b/net/mptcp/subflow.c
> > @@ -53,6 +53,40 @@ static int subflow_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
> >  	return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
> >  }
> >  
> > +static void subflow_v4_init_req(struct request_sock *req,
> > +				const struct sock *sk_listener,
> > +				struct sk_buff *skb)
> > +{
> > +	struct subflow_request_sock *subflow_req = subflow_rsk(req);
> > +	struct subflow_sock *listener = subflow_sk(sk_listener);
> > +	struct tcp_options_received rx_opt;
> > +
> > +	tcp_rsk(req)->is_mptcp = 1;
> > +	pr_debug("subflow_req=%p, listener=%p", subflow_req, listener);
> > +
> > +	tcp_request_sock_ipv4_ops.init_req(req, sk_listener, skb);
> > +
> > +	rx_opt.mptcp.flags = 0;
> > +	rx_opt.mptcp.mp_capable = 0;
> > +	rx_opt.mptcp.mp_join = 0;
> > +	rx_opt.mptcp.dss = 0;
> > +	mptcp_get_options(skb, &rx_opt);
> > +
> > +	if (rx_opt.mptcp.mp_capable && listener->request_mptcp) {
> > +		subflow_req->mp_capable = 1;
> > +		if (rx_opt.mptcp.version >= listener->version)
> > +			subflow_req->version = listener->version;
> > +		else
> > +			subflow_req->version = rx_opt.mptcp.version;
> > +		if ((rx_opt.mptcp.flags & MPTCP_CAP_CHECKSUM_REQD) ||
> > +		    listener->checksum)
> > +			subflow_req->checksum = 1;
> > +		subflow_req->remote_key = rx_opt.mptcp.sndr_key;
> > +	} else {
> > +		subflow_req->mp_capable = 0;
> > +	}
> > +}
> > +
> >  static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
> >  {
> >  	struct subflow_sock *subflow = subflow_sk(sk);
> > @@ -68,13 +102,66 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
> >  	}
> >  }
> >  
> > +static struct request_sock_ops subflow_request_sock_ops;
> > +static struct tcp_request_sock_ops subflow_request_sock_ipv4_ops;
> > +
> > +static int subflow_conn_request(struct sock *sk, struct sk_buff *skb)
> > +{
> > +	struct subflow_sock *subflow = subflow_sk(sk);
> > +
> > +	pr_debug("subflow=%p", subflow);
> > +
> > +	/* Never answer to SYNs sent to broadcast or multicast */
> > +	if (skb_rtable(skb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
> > +		goto drop;
> > +
> > +	return tcp_conn_request(&subflow_request_sock_ops,
> > +				&subflow_request_sock_ipv4_ops,
> > +				sk, skb);
> > +drop:
> > +	tcp_listendrop(sk);
> > +	return 0;
> > +}
> > +
> > +static struct sock *subflow_syn_recv_sock(const struct sock *sk,
> > +					  struct sk_buff *skb,
> > +					  struct request_sock *req,
> > +					  struct dst_entry *dst,
> > +					  struct request_sock *req_unhash,
> > +					  bool *own_req)
> > +{
> > +	struct subflow_sock *listener = subflow_sk(sk);
> > +	struct subflow_request_sock *subflow_req = subflow_rsk(req);
> > +	struct sock *child;
> > +
> > +	pr_debug("listener=%p, req=%p, conn=%p", sk, req, listener->conn);
> > +
> > +	child = tcp_v4_syn_recv_sock(sk, skb, req, dst, req_unhash, own_req);
> > +
> > +	if (child) {
> > +		struct subflow_sock *subflow = subflow_sk(child);
> > +
> > +		pr_debug("child=%p", child);
> > +		if (subflow_req->mp_capable) {
> > +			subflow->mp_capable = 1;
> > +			subflow->fourth_ack = 1;
> > +			subflow->remote_key = subflow_req->remote_key;
> > +			subflow->local_key = subflow_req->local_key;
> > +		} else {
> > +			subflow->mp_capable = 0;
> > +		}
> > +	}
> > +
> > +	return child;
> > +}
> > +
> >  const struct inet_connection_sock_af_ops subflow_specific = {
> >  	.queue_xmit	   = ip_queue_xmit,
> >  	.send_check	   = tcp_v4_send_check,
> >  	.rebuild_header	   = inet_sk_rebuild_header,
> >  	.sk_rx_dst_set	   = subflow_finish_connect,
> > -	.conn_request	   = tcp_v4_conn_request,
> > -	.syn_recv_sock	   = tcp_v4_syn_recv_sock,
> > +	.conn_request	   = subflow_conn_request,
> > +	.syn_recv_sock	   = subflow_syn_recv_sock,
> >  	.net_header_len	   = sizeof(struct iphdr),
> >  	.setsockopt	   = ip_setsockopt,
> >  	.getsockopt	   = ip_getsockopt,
> > @@ -112,6 +199,21 @@ static void subflow_close(struct sock *sk, long timeout)
> >  	tcp_close(sk, timeout);
> >  }
> >  
> > +static struct sock *subflow_accept(struct sock *sk, int flags, int *err,
> > +				   bool kern)
> > +{
> > +	struct subflow_sock *subflow = subflow_sk(sk);
> > +	struct sock *child;
> > +
> > +	pr_debug("subflow=%p, conn=%p", subflow, subflow->conn);
> > +
> > +	child = inet_csk_accept(sk, flags, err, kern);
> > +
> > +	pr_debug("child=%p", child);
> > +
> > +	return child;
> > +}
> > +
> >  static void subflow_destroy(struct sock *sk)
> >  {
> >  	pr_debug("subflow=%p", sk);
> > @@ -125,7 +227,7 @@ static struct proto subflow_prot = {
> >  	.close		= subflow_close,
> >  	.connect	= subflow_connect,
> >  	.disconnect	= tcp_disconnect,
> > -	.accept		= inet_csk_accept,
> > +	.accept		= subflow_accept,
> >  	.ioctl		= tcp_ioctl,
> >  	.init		= subflow_init_sock,
> >  	.destroy	= subflow_destroy,
> > @@ -169,7 +271,14 @@ int mptcp_subflow_init(void)
> >  
> >  	/* TODO: Register path manager callbacks. */
> >  
> > +	subflow_request_sock_ops = tcp_request_sock_ops;
> > +	subflow_request_sock_ops.obj_size = sizeof(struct subflow_request_sock),
> > +
> > +	subflow_request_sock_ipv4_ops = tcp_request_sock_ipv4_ops;
> > +	subflow_request_sock_ipv4_ops.init_req = subflow_v4_init_req;
> > +
> >  	subflow_prot.twsk_prot		= tcp_prot.twsk_prot;
> > +	subflow_prot.rsk_prot		= &subflow_request_sock_ops;
> >  	subflow_prot.h.hashinfo		= tcp_prot.h.hashinfo;
> >  	err = proto_register(&subflow_prot, 1);
> >  	if (err)
> > -- 
> > 2.19.1
> > 
> > _______________________________________________
> > mptcp mailing list
> > mptcp(a)lists.01.org
> > https://lists.01.org/mailman/listinfo/mptcp
> 
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