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Date:	Sun, 1 Jul 2012 08:47:50 -0400
From:	Neil Horman <>
To:	David Miller <>
Subject: Re: [PATCH v6] sctp: be more restrictive in transport selection on
 bundled sacks

On Sat, Jun 30, 2012 at 05:39:45PM -0700, David Miller wrote:
> From: Neil Horman <>
> Date: Sat, 30 Jun 2012 09:04:26 -0400
> > It was noticed recently that when we send data on a transport, its possible that
> > we might bundle a sack that arrived on a different transport.  While this isn't
> > a major problem, it does go against the SHOULD requirement in section 6.4 of RFC
> > 2960:
> > 
> >  An endpoint SHOULD transmit reply chunks (e.g., SACK, HEARTBEAT ACK,
> >    etc.) to the same destination transport address from which it
> >    received the DATA or control chunk to which it is replying.  This
> >    rule should also be followed if the endpoint is bundling DATA chunks
> >    together with the reply chunk.
> > 
> > This patch seeks to correct that.  It restricts the bundling of sack operations
> > to only those transports which have moved the ctsn of the association forward
> > since the last sack.  By doing this we guarantee that we only bundle outbound
> > saks on a transport that has received a chunk since the last sack.  This brings
> > us into stricter compliance with the RFC.
> > 
> > Vlad had initially suggested that we strictly allow only sack bundling on the
> > transport that last moved the ctsn forward.  While this makes sense, I was
> > concerned that doing so prevented us from bundling in the case where we had
> > received chunks that moved the ctsn on multiple transports.  In those cases, the
> > RFC allows us to select any of the transports having received chunks to bundle
> > the sack on.  so I've modified the approach to allow for that, by adding a state
> > variable to each transport that tracks weather it has moved the ctsn since the
> > last sack.  This I think keeps our behavior (and performance), close enough to
> > our current profile that I think we can do this without a sysctl knob to
> > enable/disable it.
> > 
> > Signed-off-by: Neil Horman <>
> > CC: Vlad Yaseivch <>
> > CC: David S. Miller <>
> > CC:
> > Reported-by: Michele Baldessari <>
> > Reported-by: sorin serban <>
> Once this has Vlad's ACK I'll apply it.
> There has to be a better way to handle this situation, wherein the
> responsible party has ACK'd the patch but I just ask for a few coding
> style fixups and whatnot.  As it stands now I have to twiddle my
> thumbs waiting for the new ACK.
Perhaps we could modify the SubmittingPatches document to indicate that an
Acked-by from a subsystem maintainer implicitly confers authority on the
upstream receiver to request reasonable stylistic changes that don't affect the
functionality of the patch in the interests of maintaining coding conventions.

i.e. Since vlad applied an acked-by to v5 of this patch, that would give you the
right to carry that ack forward to v6 because you only asked for style changes.


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