Re: [PATCH net-next v3 1/6] tcp: implement RFC 7323 window retraction receiver requirements

[Simon Baatz <gmbnomis@gmail.com>]

Hi Stefano,

On Tue, Mar 10, 2026 at 09:58:07AM +0100, Stefano Brivio wrote:
> Simon,
> 
> On Mon, 09 Mar 2026 09:02:26 +0100
> Simon Baatz via B4 Relay <devnull+gmbnomis.gmail.com@kernel.org> wrote:
> 
> > [...]
> >
> > diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> > index f72eef31fa23cc584f2f0cefacdc35cae43aa52d..73aa2e0ccd1d7a6314a00c27950b019b62a3851c 100644
> > --- a/include/linux/tcp.h
> > +++ b/include/linux/tcp.h
> > @@ -316,6 +316,9 @@ struct tcp_sock {
> >  					*/
> >  	u32	app_limited;	/* limited until "delivered" reaches this val */
> >  	u32	rcv_wnd;	/* Current receiver window		*/
> > +	u32	rcv_mwnd_seq;	/* Maximum window sequence number (RFC 7323,
> > +				 * section 2.4, receiver requirements)
> > +				 */
> 
> I didn't follow the rest of the discussion but, at this point, what
> does this mean for applications (CRIU, passt) dumping/restoring socket
> data? Do they have to adapt? I couldn't find this bit of information
> anywhere in v3.

Based on our discussion, the "Setting the TCP_REPAIR_WINDOW socket
option initializes rcv_mwnd_seq" v2 change addresses TCP window
restoration.  As we said that information about window retraction is
not crucial, the window will be restored as "non-retracted", matching
prior behavior.  Therefore, there is no change to the information
that applications need to dump or restore.

-- 
Simon Baatz <gmbnomis@gmail.com>