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Commit b1ed4c4f authored by Andrey Vagin's avatar Andrey Vagin Committed by David S. Miller
Browse files

tcp: add an ability to dump and restore window parameters 



We found that sometimes a restored tcp socket doesn't work.

A reason of this bug is incorrect window parameters and in this case
tcp_acceptable_seq() returns tcp_wnd_end(tp) instead of tp->snd_nxt. The
other side drops packets with this seq, because seq is less than
tp->rcv_nxt ( tcp_sequence() ).

Data from a send queue is sent only if there is enough space in a
window, so when we restore unacked data, we need to expand a window to
fit this data.

This was in a first version of this patch:
"tcp: extend window to fit all restored unacked data in a send queue"

Then Alexey recommended me to restore window parameters instead of
adjusted them according with data in a sent queue. This sounds resonable.

rcv_wnd has to be restored, because it was reported to another side
and the offered window is never shrunk.
One of reasons why we need to restore snd_wnd was described above.

Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: James Morris <jmorris@namei.org>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Patrick McHardy <kaber@trash.net>
Signed-off-by: default avatarAndrey Vagin <avagin@openvz.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 641f7e40

include/uapi/linux/tcp.h

+10 −0
Original line number Diff line number Diff line
@@ -115,12 +115,22 @@ enum { 
#define TCP_CC_INFO		26	/* Get Congestion Control (optional) info */

#define TCP_SAVE_SYN		27	/* Record SYN headers for new connections */

#define TCP_SAVED_SYN		28	/* Get SYN headers recorded for connection */

#define TCP_REPAIR_WINDOW	29	/* Get/set window parameters */



struct tcp_repair_opt {

	__u32	opt_code;

	__u32	opt_val;

};



struct tcp_repair_window {

	__u32	snd_wl1;

	__u32	snd_wnd;

	__u32	max_window;



	__u32	rcv_wnd;

	__u32	rcv_wup;

};



enum {

	TCP_NO_QUEUE,

	TCP_RECV_QUEUE,

net/ipv4/tcp.c

+57 −0
Original line number Diff line number Diff line
@@ -2277,6 +2277,38 @@ static inline bool tcp_can_repair_sock(const struct sock *sk) 
		((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_ESTABLISHED));

}



static int tcp_repair_set_window(struct tcp_sock *tp, char __user *optbuf, int len)

{

	struct tcp_repair_window opt;



	if (!tp->repair)

		return -EPERM;



	if (len != sizeof(opt))

		return -EINVAL;



	if (copy_from_user(&opt, optbuf, sizeof(opt)))

		return -EFAULT;



	if (opt.max_window < opt.snd_wnd)

		return -EINVAL;



	if (after(opt.snd_wl1, tp->rcv_nxt + opt.rcv_wnd))

		return -EINVAL;



	if (after(opt.rcv_wup, tp->rcv_nxt))

		return -EINVAL;



	tp->snd_wl1	= opt.snd_wl1;

	tp->snd_wnd	= opt.snd_wnd;

	tp->max_window	= opt.max_window;



	tp->rcv_wnd	= opt.rcv_wnd;

	tp->rcv_wup	= opt.rcv_wup;



	return 0;

}



static int tcp_repair_options_est(struct tcp_sock *tp,

		struct tcp_repair_opt __user *optbuf, unsigned int len)

{
@@ -2604,6 +2636,9 @@ static int do_tcp_setsockopt(struct sock *sk, int level, 
		else

			tp->tsoffset = val - tcp_time_stamp;

		break;

	case TCP_REPAIR_WINDOW:

		err = tcp_repair_set_window(tp, optval, optlen);

		break;

	case TCP_NOTSENT_LOWAT:

		tp->notsent_lowat = val;

		sk->sk_write_space(sk);
@@ -2860,6 +2895,28 @@ static int do_tcp_getsockopt(struct sock *sk, int level, 
			return -EINVAL;

		break;



	case TCP_REPAIR_WINDOW: {

		struct tcp_repair_window opt;



		if (get_user(len, optlen))

			return -EFAULT;



		if (len != sizeof(opt))

			return -EINVAL;



		if (!tp->repair)

			return -EPERM;



		opt.snd_wl1	= tp->snd_wl1;

		opt.snd_wnd	= tp->snd_wnd;

		opt.max_window	= tp->max_window;

		opt.rcv_wnd	= tp->rcv_wnd;

		opt.rcv_wup	= tp->rcv_wup;



		if (copy_to_user(optval, &opt, len))

			return -EFAULT;

		return 0;

	}

	case TCP_QUEUE_SEQ:

		if (tp->repair_queue == TCP_SEND_QUEUE)

			val = tp->write_seq;