From mboxrd@z Thu Jan  1 00:00:00 1970
Content-Type: multipart/mixed; boundary="===============2453163313727604250=="
MIME-Version: 1.0
From: Christoph Paasch <cpaasch at apple.com>
To: mptcp at lists.01.org
Subject: Re: [MPTCP] [PATCH 1/2] skbuff: Add shared control buffer
Date: Wed, 08 Nov 2017 09:25:52 +0900
Message-ID: <20171108002552.GK5226@Chimay.local>
In-Reply-To: d8c5760d-5716-98f1-22b8-13f17b4bb8b3@oracle.com
X-Status: 
X-Keywords:                  
X-UID: 160

--===============2453163313727604250==
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable

On 07/11/17 - 15:23:42, Rao Shoaib wrote:
> =

> =

> On 11/07/2017 01:15 PM, Christoph Paasch wrote:
> > hese are meta-level retransmissions that are being sent on a different
> > subflow and/or on the same subflow but with new TCP sequence numbers an=
d a
> > new DSS-mapping. These indeed end up going through mptcp_skb_entail().
> > =

> > The retransmissions I mean are the TCP-level retransmissions (aka.,
> > fast-retransmits, tail-loss-probe, RTO,...). They don't go through
> > mptcp_skb_entail again.
> > =

> > I will take a look at the trace in the other mail.
> > =

> > =

> > Christoph
> RTO will go through this code.
> Partial ACK and fast-retransmit etc are fine if they are transmitted with
> the same mapping (or else DSS will fail as well) In fact it is required. =
On
> the receiver an adjustment is made for the TCP flow's seq number.=C2=A0 S=
ee
> mptcp_detect_mapping() it requires that the (partial)=C2=A0 skb has the e=
xact
> same mapping as if it was transmitted as part of the original skb and than
> look at mptcp_validate_mapping() and mptcp_prepare_skb() that adjust the
> data sequence number based on the tcp sequence number of the packet.
> =

> If not than can you explain how the current mechanism works and what happ=
ens
> to the DSS settings in case of retransmission. Where/How does it gets
> updated because mptcp_options_write() only does a copy with the updated A=
CK.

The way it is handled currently is that the mapping is decided during
mptcp_skb_entail(), which writes the mapping to the skb->cb.

>From that moment on it won't change anymore and, as you know, it will simp=
ly
get copied from the skb->cb to the TCP-header in mptcp_options_write().


Christoph

> =

> When I have some more time I will verify by hacking the kernel. Sorry I c=
an
> not upload the complete kernel as it is a mess right now, I changed a lot=
 of
> things, that is why it has taken this long to even get ssh working. I will
> try to get you just the patch for this fix.
> =

> Shoaib

--===============2453163313727604250==--