[CRIU] [PATCH 3/3] tcp: add ability to restore a fin packet

[Kir Kolyshkin]

On 03/04/2014 09:18 PM, Andrey Vagin wrote:
> It's required for restoring sockets in closing states:
> TCP_FIN_WAIT{1,2}, TCP_WAIT_STOP, TCP_CLOSING, TCP_LAST_ACK.
>
> A fin packet is restored by sending the conntroll message. This

Sorry I can't help myself to refrain from asking.
Is this word an abbreviation for "connection trolling"?

> interface is choosen, because we are goint to use sendmsg to restore
> sockets in TCP_SYN_SENT and TCP_SYN_RECV states.
>
> Requests in the TCP_SYN_RECV state will be restored by sending messages
> in a proper listen socket. A message will contain address and a conntrol
> messages with sequence numbers.
>
> Sockets in the TCP_SYN_SENT state will be restored by sending messages
> in an unconnected tcp socket. A message will contain remote address and
> an initial sequence number.
>
> Signed-off-by: Andrey Vagin <avagin at openvz.org>
> ---
>   include/net/tcp.h        |  1 +
>   include/uapi/linux/tcp.h |  3 +++
>   net/ipv4/tcp.c           | 39 +++++++++++++++++++++++++++++++++++++++
>   net/ipv4/tcp_input.c     |  2 +-
>   4 files changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 56fc366..ca3bd0b 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -561,6 +561,7 @@ void tcp_cwnd_application_limited(struct sock *sk);
>   void tcp_resume_early_retransmit(struct sock *sk);
>   void tcp_rearm_rto(struct sock *sk);
>   void tcp_reset(struct sock *sk);
> +void tcp_fin(struct sock *sk);
>   
>   /* tcp_timer.c */
>   void tcp_init_xmit_timers(struct sock *);
> diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
> index 377f1e5..2cc6876 100644
> --- a/include/uapi/linux/tcp.h
> +++ b/include/uapi/linux/tcp.h
> @@ -199,4 +199,7 @@ struct tcp_md5sig {
>   	__u8	tcpm_key[TCP_MD5SIG_MAXKEYLEN];		/* key (binary) */
>   };
>   
> +/* Conntroll message types to repair tcp connections */
> +#define TCP_REPAIR_SEND_FIN	1
> +
>   #endif /* _UAPI_LINUX_TCP_H */
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 9a23905..308f7aa 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1068,6 +1068,34 @@ static int tcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg, int *size)
>   	return err;
>   }
>   
> +static int tcp_repair_cmsg(struct sock *sk, struct msghdr *msg)
> +{
> +	struct tcp_sock *tp = tcp_sk(sk);
> +	struct cmsghdr *cmsg;
> +
> +	for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg)) {
> +		if (!CMSG_OK(msg, cmsg))
> +			return -EINVAL;
> +		if (cmsg->cmsg_level != SOL_TCP)
> +			continue;
> +
> +		switch (cmsg->cmsg_type) {
> +		case TCP_REPAIR_SEND_FIN:
> +			if (tp->repair_queue == TCP_RECV_QUEUE)
> +				tcp_fin(sk);
> +			else if (tp->repair_queue == TCP_SEND_QUEUE)
> +				tcp_shutdown(sk, SEND_SHUTDOWN);
> +			else
> +				return -EINVAL;
> +			break;
> +		default:
> +			return -EINVAL;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>   int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
>   		size_t size)
>   {
> @@ -1084,6 +1112,17 @@ int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
>   	flags = msg->msg_flags;
>   
>   	if (unlikely(tp->repair)) {
> +		if (msg->msg_controllen) {
> +			if (size != 0)
> +				return -EINVAL;
> +
> +			err = tcp_repair_cmsg(sk, msg);
> +			if (err < 0)
> +				goto out_err;
> +
> +			goto out;
> +		}
> +
>   		if (tp->repair_queue == TCP_RECV_QUEUE) {
>   			copied = tcp_send_rcvq(sk, msg, size);
>   			goto out;
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 227cba7..b68ffcd 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -3819,7 +3819,7 @@ void tcp_reset(struct sock *sk)
>    *
>    *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
>    */
> -static void tcp_fin(struct sock *sk)
> +void tcp_fin(struct sock *sk)
>   {
>   	struct tcp_sock *tp = tcp_sk(sk);
>   	const struct dst_entry *dst;