[CRIU] Re: [PATCH] tcp: restore rcv_wscale in a repair mode

[Pavel Emelyanov]

On 09/10/2012 03:54 PM, Andrew Vagin wrote:
> rcv_wscale is a symetric parameter with snd_wscale.
> 
> Both this parameters are set on a connection handshake.
> 
> Without this valuea remote window size can't be interpreted correctly,
> because a value from a packet should be shifted on rcv_wscale.
> 
> And one more thing is that we should set wscale_ok too.
> 
> This patch doesn't break a back compatibility, a rcv window
> will be restored with the same bug (rcv_wscale = 0).
> 
> Signed-off-by: Andrew Vagin <avagin at openvz.org>
> ---
>  net/ipv4/tcp.c |   20 ++++++++++++++++----
>  1 files changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 2109ff4..70d995c 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2325,10 +2325,22 @@ static int tcp_repair_options_est(struct tcp_sock *tp,
>  			tp->rx_opt.mss_clamp = opt.opt_val;
>  			break;
>  		case TCPOPT_WINDOW:
> -			if (opt.opt_val > 14)
> -				return -EFBIG;
> -
> -			tp->rx_opt.snd_wscale = opt.opt_val;
> +			{
> +				union {
> +					struct {
> +						u16 snd_wscale;
> +						u16 rcv_wscale;
> +					};
> +					u32 raw;
> +				} val = { .raw = opt.opt_val };

Can we make it with bits shifts and masking?

> +
> +				if (val.snd_wscale > 14 || val.rcv_wscale > 14)
> +					return -EFBIG;
> +
> +				tp->rx_opt.snd_wscale = val.snd_wscale;
> +				tp->rx_opt.rcv_wscale = val.rcv_wscale;
> +				tp->rx_opt.wscale_ok = 1;
> +			}
>  			break;
>  		case TCPOPT_SACK_PERM:
>  			if (opt.opt_val != 0)