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, 142 deletions

diff --git a/net/dccp/ccids/lib/packet_history.h b/net/dccp/ccids/lib/packet_history.h
deleted file mode 100644
index 159cc9326eab..000000000000
--- a/net/dccp/ccids/lib/packet_history.h
+++ /dev/null
@@ -1,142 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-or-later */
-/*
- *  Packet RX/TX history data structures and routines for TFRC-based protocols.
- *
- *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
- *  Copyright (c) 2005-6 The University of Waikato, Hamilton, New Zealand.
- *
- *  This code has been developed by the University of Waikato WAND
- *  research group. For further information please see https://www.wand.net.nz/
- *  or e-mail Ian McDonald - ian.mcdonald@jandi.co.nz
- *
- *  This code also uses code from Lulea University, rereleased as GPL by its
- *  authors:
- *  Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
- *
- *  Changes to meet Linux coding standards, to make it meet latest ccid3 draft
- *  and to make it work as a loadable module in the DCCP stack written by
- *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>.
- *
- *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
- */
-
-#ifndef _DCCP_PKT_HIST_
-#define _DCCP_PKT_HIST_
-
-#include <linux/list.h>
-#include <linux/slab.h>
-#include "tfrc.h"
-
-/**
- *  tfrc_tx_hist_entry  -  Simple singly-linked TX history list
- *  @next:  next oldest entry (LIFO order)
- *  @seqno: sequence number of this entry
- *  @stamp: send time of packet with sequence number @seqno
- */
-struct tfrc_tx_hist_entry {
-	struct tfrc_tx_hist_entry *next;
-	u64			  seqno;
-	ktime_t			  stamp;
-};
-
-static inline struct tfrc_tx_hist_entry *
-	tfrc_tx_hist_find_entry(struct tfrc_tx_hist_entry *head, u64 seqno)
-{
-	while (head != NULL && head->seqno != seqno)
-		head = head->next;
-	return head;
-}
-
-int tfrc_tx_hist_add(struct tfrc_tx_hist_entry **headp, u64 seqno);
-void tfrc_tx_hist_purge(struct tfrc_tx_hist_entry **headp);
-
-/* Subtraction a-b modulo-16, respects circular wrap-around */
-#define SUB16(a, b) (((a) + 16 - (b)) & 0xF)
-
-/* Number of packets to wait after a missing packet (RFC 4342, 6.1) */
-#define TFRC_NDUPACK 3
-
-/**
- * tfrc_rx_hist_entry - Store information about a single received packet
- * @tfrchrx_seqno:	DCCP packet sequence number
- * @tfrchrx_ccval:	window counter value of packet (RFC 4342, 8.1)
- * @tfrchrx_ndp:	the NDP count (if any) of the packet
- * @tfrchrx_tstamp:	actual receive time of packet
- */
-struct tfrc_rx_hist_entry {
-	u64		 tfrchrx_seqno:48,
-			 tfrchrx_ccval:4,
-			 tfrchrx_type:4;
-	u64		 tfrchrx_ndp:48;
-	ktime_t		 tfrchrx_tstamp;
-};
-
-/**
- * tfrc_rx_hist  -  RX history structure for TFRC-based protocols
- * @ring:		Packet history for RTT sampling and loss detection
- * @loss_count:		Number of entries in circular history
- * @loss_start:		Movable index (for loss detection)
- * @rtt_sample_prev:	Used during RTT sampling, points to candidate entry
- */
-struct tfrc_rx_hist {
-	struct tfrc_rx_hist_entry *ring[TFRC_NDUPACK + 1];
-	u8			  loss_count:2,
-				  loss_start:2;
-#define rtt_sample_prev		  loss_start
-};
-
-/**
- * tfrc_rx_hist_index - index to reach n-th entry after loss_start
- */
-static inline u8 tfrc_rx_hist_index(const struct tfrc_rx_hist *h, const u8 n)
-{
-	return (h->loss_start + n) & TFRC_NDUPACK;
-}
-
-/**
- * tfrc_rx_hist_last_rcv - entry with highest-received-seqno so far
- */
-static inline struct tfrc_rx_hist_entry *
-			tfrc_rx_hist_last_rcv(const struct tfrc_rx_hist *h)
-{
-	return h->ring[tfrc_rx_hist_index(h, h->loss_count)];
-}
-
-/**
- * tfrc_rx_hist_entry - return the n-th history entry after loss_start
- */
-static inline struct tfrc_rx_hist_entry *
-			tfrc_rx_hist_entry(const struct tfrc_rx_hist *h, const u8 n)
-{
-	return h->ring[tfrc_rx_hist_index(h, n)];
-}
-
-/**
- * tfrc_rx_hist_loss_prev - entry with highest-received-seqno before loss was detected
- */
-static inline struct tfrc_rx_hist_entry *
-			tfrc_rx_hist_loss_prev(const struct tfrc_rx_hist *h)
-{
-	return h->ring[h->loss_start];
-}
-
-/* indicate whether previously a packet was detected missing */
-static inline bool tfrc_rx_hist_loss_pending(const struct tfrc_rx_hist *h)
-{
-	return h->loss_count > 0;
-}
-
-void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h, const struct sk_buff *skb,
-			     const u64 ndp);
-
-int tfrc_rx_hist_duplicate(struct tfrc_rx_hist *h, struct sk_buff *skb);
-
-struct tfrc_loss_hist;
-int tfrc_rx_handle_loss(struct tfrc_rx_hist *h, struct tfrc_loss_hist *lh,
-			struct sk_buff *skb, const u64 ndp,
-			u32 (*first_li)(struct sock *sk), struct sock *sk);
-u32 tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb);
-int tfrc_rx_hist_alloc(struct tfrc_rx_hist *h);
-void tfrc_rx_hist_purge(struct tfrc_rx_hist *h);
-
-#endif /* _DCCP_PKT_HIST_ */