Re: [PATCH v1 net-next 2/4] net: Retire DCCP.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Pablo Neira Ayuso <pablo@netfilter.org>
Date: Tue, 8 Apr 2025 18:37:36 +0200
> Hi Kuniyuki,
> 
> On Mon, Apr 07, 2025 at 04:17:49PM -0700, Kuniyuki Iwashima wrote:
> > DCCP was orphaned in 2021 by commit 054c4610bd05 ("MAINTAINERS: dccp:
> > move Gerrit Renker to CREDITS"), which noted that the last maintainer
> > had been inactive for five years.
> > 
> > In recent years, it has become a playground for syzbot, and most changes
> > to DCCP have been odd bug fixes triggered by syzbot.  Apart from that,
> > the only changes have been driven by treewide or networking API updates
> > or adjustments related to TCP.
> > 
> > Thus, in 2023, we announced we would remove DCCP in 2025 via commit
> > b144fcaf46d4 ("dccp: Print deprecation notice.").
> > 
> > Since then, only one individual has contacted the netdev mailing list. [0]
> > 
> > There is ongoing research for Multipath DCCP.  The repository is hosted
> > on GitHub [1], and development is not taking place through the upstream
> > community.  While the repository is published under the GPLv2 license,
> > the scheduling part remains proprietary, with a LICENSE file [2] stating:
> > 
> >   "This is not Open Source software."
> >
> > The researcher mentioned a plan to address the licensing issue, upstream
> > the patches, and step up as a maintainer, but there has been no further
> > communication since then.
> > 
> > Maintaining DCCP for a decade without any real users has become a burden.
> >
> > Therefore, it's time to remove it.
> > 
> > Removing DCCP will also provide significant benefits to TCP.  It allows
> > us to freely reorganize the layout of struct inet_connection_sock, which
> > is currently shared with DCCP, and optimize it to reduce the number of
> > cachelines accessed in the TCP fast path.
> 
> Netfilter parses skbuffs, in that sense, it is a middlebox. Main
> concern on my side is that it could break rulesets, even for people
> that don't really see dccp traffic ever, ruleset could stop loading.
> 
> I would keep the netfilter bits aside by now, based on your netfilter
> updates, we can internally discuss how to phase out dccp support to
> get aligned with netdev maintainers, as it seems there is a wish to
> reduce debt in this front.

Fair enough.  I'll drop the netfilter stuff in v2.


> 
> Having said, this Netfilter does not rely on any of this socket
> structures, I think it should not be an impediment for your tree
> spring cleanup (IIRC we have no hard dependencies on CONFIG_DCCP).

Yes, actually I split changes for net/dccp, netfilter, and LSM
initially, and then, even without net/dccp, netfilter compiled
successfully if include/linux/dccp.h (dccp_hdr etc) was not removed.

Thanks!

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