net: Retire DCCP socket.

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.

Note that we keep DCCP netfilter modules as requested.  [3]

Link: https://lore.kernel.org/netdev/20230710182253.81446-1-kuniyu@amazon.com/T/#u #[0]
Link: https://github.com/telekom/mp-dccp #[1]
Link: https://github.com/telekom/mp-dccp/blob/mpdccp_v03_k5.10/net/dccp/non_gpl_scheduler/LICENSE #[2]
Link: https://lore.kernel.org/netdev/Z_VQ0KlCRkqYWXa-@calendula/ #[3]
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Paul Moore <paul@paul-moore.com> (LSM and SELinux)
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Link: https://patch.msgid.link/20250410023921.11307-3-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 0 insertions, 51 deletions

diff --git a/include/linux/tfrc.h b/include/linux/tfrc.h
deleted file mode 100644
index a5acc768085d..000000000000
--- a/include/linux/tfrc.h
+++ /dev/null
@@ -1,51 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-or-later */
-#ifndef _LINUX_TFRC_H_
-#define _LINUX_TFRC_H_
-/*
- *  TFRC - Data Structures for the TCP-Friendly Rate Control congestion
- *         control mechanism as specified in RFC 3448.
- *
- *  Copyright (c) 2005 The University of Waikato, Hamilton, New Zealand.
- *  Copyright (c) 2005 Ian McDonald <iam4@cs.waikato.ac.nz>
- *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
- *  Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
- */
-#include <linux/types.h>
-
-/** 	tfrc_rx_info    -    TFRC Receiver Data Structure
- *
- * 	@tfrcrx_x_recv:	receiver estimate of sending rate (3.2.2)
- * 	@tfrcrx_rtt:	round-trip-time (communicated by sender)
- * 	@tfrcrx_p:	current estimate of loss event rate (3.2.2)
- */
-struct tfrc_rx_info {
-  	__u32 tfrcrx_x_recv;
-	__u32 tfrcrx_rtt;
-  	__u32 tfrcrx_p;
-};
-
-/** 	tfrc_tx_info    -    TFRC Sender Data Structure
- *
- * 	@tfrctx_x:	computed transmit rate (4.3 (4))
- * 	@tfrctx_x_recv: receiver estimate of send rate (4.3)
- * 	@tfrctx_x_calc:	return value of throughput equation (3.1)
- * 	@tfrctx_rtt:	(moving average) estimate of RTT (4.3)
- * 	@tfrctx_p:	current loss event rate (5.4)
- * 	@tfrctx_rto:	estimate of RTO, equals 4*RTT (4.3)
- * 	@tfrctx_ipi:	inter-packet interval (4.6)
- *
- *  Note: X and X_recv are both maintained in units of 64 * bytes/second. This
- *        enables a finer resolution of sending rates and avoids problems with
- *        integer arithmetic; u32 is not sufficient as scaling consumes 6 bits.
- */
-struct tfrc_tx_info {
-	__u64 tfrctx_x;
-	__u64 tfrctx_x_recv;
-	__u32 tfrctx_x_calc;
-	__u32 tfrctx_rtt;
-	__u32 tfrctx_p;
-	__u32 tfrctx_rto;
-	__u32 tfrctx_ipi;
-};
-
-#endif /* _LINUX_TFRC_H_ */