Subject: Re: [PATCH] UDPCP Communication Protocol

From: Stefani Seibold <[email-masked]>
Date: Fri, 31 Dec 2010 11:22:59 +0100

Am Freitag, den 31.12.2010, 11:00 +0100 schrieb Eric Dumazet:
> Le vendredi 31 décembre 2010 à 10:29 +0100, [email-masked] a
> écrit :
> > From: Stefani Seibold <[email-masked]>
> > 
> >  
> >  /*
> >   *	Handle MSG_ERRQUEUE
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index 2d3ded4..f9890a2 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -1310,7 +1310,7 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
> >  	if (inet_sk(sk)->inet_daddr)
> >  		sock_rps_save_rxhash(sk, skb->rxhash);
> >  
> > -	rc = ip_queue_rcv_skb(sk, skb);
> > +	rc = sock_queue_rcv_skb(sk, skb);
> 
> Ouch... Care to explain why you changed this part ???
> 
> You just destroyed commit f84af32cbca70a intent, without any word in
> your changelog. Making UDP slower, while others try to speed it must be
> explained and advertised.
>  
> In general, we prefer a preliminary patch introducing all the changes in
> current stack, then another one with the new protocol.
> 

I reverted this for two reasons:

First ip_queue_rcv_skb drops the dst entry, which breaks the user land
application which expect packet info after a

setsockopt(handle, IPPROTO_IP, IP_PKTINFO, &const_int_1, sizeof(int));

But for packets already in the queue this information will be lost. So
it is a potential race condition.

Second it breaks my UDPCP communication protocol stack module, which
works very well till 2.6.35. I need this information in the data_ready()
function to generate an ACK.