Re: [MPTCP] [PATCH 05/18] tcp6: Prepare for maximum TCP option-space

[Christoph Paasch <cpaasch at apple.com>]

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On 04/10/17 - 15:33:35, Mat Martineau wrote:
> 
> On Tue, 3 Oct 2017, Christoph Paasch wrote:
> 
> > With a generic TCP-option framework we don't know in advance how much
> > space will be used. So, estimate the worst and allocate the maximum.
> > Later on, we pull skb->tail back in again.
> 
> v2 of the option registration patch will conflict with this. The prepare
> callback does figure out the number of option bytes required before writing
> to the outgoing skb, so that can happen before the alloc_skb().

No worries, I will take care of the conflicts.

Will be working on a v2 of my patchset to handle the incoming data path as
well.


Christoph

> 
> 
> Mat
> 
> 
> > 
> > Signed-off-by: Christoph Paasch <cpaasch(a)apple.com>
> > ---
> > net/ipv6/tcp_ipv6.c | 16 ++++++++--------
> > 1 file changed, 8 insertions(+), 8 deletions(-)
> > 
> > diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> > index 64d94afa427f..17f7e0cd8755 100644
> > --- a/net/ipv6/tcp_ipv6.c
> > +++ b/net/ipv6/tcp_ipv6.c
> > @@ -784,17 +784,11 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
> > 	struct flowi6 fl6;
> > 	struct net *net = sk ? sock_net(sk) : dev_net(skb_dst(skb)->dev);
> > 	struct sock *ctl_sk = net->ipv6.tcp_sk;
> > -	unsigned int tot_len = sizeof(struct tcphdr);
> > +	unsigned int tot_len = sizeof(struct tcphdr) + MAX_TCP_OPTION_SPACE;
> > +	unsigned int reduce = 0; /* By how much to pull skb->tail back in? */
> > 	struct dst_entry *dst;
> > 	__be32 *topt;
> > 
> > -	if (tsecr)
> > -		tot_len += TCPOLEN_TSTAMP_ALIGNED;
> > -#ifdef CONFIG_TCP_MD5SIG
> > -	if (key)
> > -		tot_len += TCPOLEN_MD5SIG_ALIGNED;
> > -#endif
> > -
> > 	buff = alloc_skb(MAX_HEADER + sizeof(struct ipv6hdr) + tot_len,
> > 			 GFP_ATOMIC);
> > 	if (!buff)
> > @@ -823,6 +817,8 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
> > 				(TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP);
> > 		*topt++ = htonl(tsval);
> > 		*topt++ = htonl(tsecr);
> > +
> > +		reduce += TCPOLEN_TSTAMP_ALIGNED;
> > 	}
> > 
> > #ifdef CONFIG_TCP_MD5SIG
> > @@ -832,9 +828,13 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
> > 		tcp_v6_md5_hash_hdr((__u8 *)topt, key,
> > 				    &ipv6_hdr(skb)->saddr,
> > 				    &ipv6_hdr(skb)->daddr, t1);
> > +
> > +		reduce += TCPOLEN_MD5SIG_ALIGNED;
> > 	}
> > #endif
> > 
> > +	buff->tail -= reduce;
> > +
> > 	memset(&fl6, 0, sizeof(fl6));
> > 	fl6.daddr = ipv6_hdr(skb)->saddr;
> > 	fl6.saddr = ipv6_hdr(skb)->daddr;
> > -- 
> > 2.14.1
> > 
> > 
> 
> --
> Mat Martineau
> Intel OTC