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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>
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Add description for `tfrc_invert_loss_event_rate` to fix the W=1 warnings:
net/dccp/ccids/lib/tfrc_equation.c:695: warning: Function parameter or
member 'loss_event_rate' not described in 'tfrc_invert_loss_event_rate'
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Richard Sailer <richard_siegfried@systemli.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Based on 1 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-or-later
has been chosen to replace the boilerplate/reference in 3029 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070032.746973796@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Fix incorrect start markers, wrapped summary lines, missing section
breaks, incorrect separators, and some name mismatches.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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This adds a function to take care of the following, separate cases occurring in
the computation of the Loss Rate p:
* 1/(2^32-1) is mapped into 0% as per RFC 4342, 8.5;
* 1/0 is mapped into 100%, the maximum;
* to avoid that p = 1/x is rounded down to 0 when x is very large, since this
means accidentally re-entering slow-start indicated by p == 0, the minimum
resolution value of p is now returned instead;
* a bug in ccid3_hc_rx_getsockopt is fixed: 1/0 was mapped into ~0U.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
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No code change, cosmetical changes only:
* whitespace cleanup via scripts/cleanfile,
* remove self-references to filename at top of files,
* fix coding style (extraneous brackets),
* fix documentation style (kernel-doc-nano-HOWTO).
Thanks are due to Ivo Augusto Calado who raised these issues by
submitting good-quality patches.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
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This patch integrates the TFRC library, which is a dependency of CCID-3 (and
CCID-4), with the new use of CCIDs in the DCCP module.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
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This fixes a bug in the reverse lookup of p: given a value f(p), instead of p,
the function returned the smallest tabulated value f(p).
The smallest tabulated value of
10^6 * f(p) = sqrt(2*p/3) + 12 * sqrt(3*p/8) * (32 * p^3 + p)
for p=0.0001 is 8172.
Since this value is scaled by 10^6, the outcome of this bug is that a loss
of 8172/10^6 = 0.8172% was reported whenever the input was below the table
resolution of 0.01%.
This means that the value was over 80 times too high, resulting in large spikes
of the initial loss interval, thus unnecessarily reducing the throughput.
Also corrected the printk format (%u for u32).
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
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Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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In migrating towards using the newer functions scaled_div/scaled_div32
for TFRC computations mapped from floating-point onto integer arithmetic,
this completes the last stage of modifications.
In particular, the overflow case for computing X_calc is circumvented by
* breaking the computation into two stages
* the first stage, res = (s*1E6)/R, cannot overflow due to use of u64
* in the second stage, res = (res*1E6)/f, overflow on u32 is avoided due
to (i) returning UINT_MAX in this case (which is logically appropriate)
and (ii) issuing a warning message into the system log (since very likely
there is a problem somewhere else with the parameters)
Lastly, all such scaling operations are now exported into tfrc.h, since
actually this form of scaled computation is specific to TFRC and not to CCID3.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
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This replaces the linear search algorithm for reverse lookup with
binary search.
It has the advantage of better scalability: O(log2(N)) instead of O(N).
This means that the average number of iterations is reduced from 250
(linear search if each value appears equally likely) down to at most 9.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
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This
* adds documentation about the lowest resolution that is possible within
the bounds of the current lookup table
* defines a constant TFRC_SMALLEST_P which defines this resolution
* issues a warning if a given value of p is below resolution
* combines two previously adjacent if-blocks of nearly identical
structure into one
This patch does not change the algorithm as such.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
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1) For the forward X_calc lookup, it
* protects effectively against RTT=0 (this case is possible), by
returning the maximal lookup value instead of just setting it to 1
* reformulates the array-bounds exceeded condition: this only happens
if p is greater than 1E6 (due to the scaling)
* the case of negative indices can now with certainty be excluded,
since documentation shows that the formulas are within bounds
* additional protection against p = 0 (would give divide-by-zero)
2) For the reverse lookup, it warns against
* protects against exceeding array bounds
* now returns 0 if f(p) = 0, due to function definition
* warns about minimal resolution error and returns the smallest table
value instead of p=0 [this would mask congestion conditions]
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
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This fixes the following small error in tfrc_calc_x_reverse_lookup.
1) The table is generated by the following equations:
lookup[index][0] = g((index+1) * 1000000/TFRC_CALC_X_ARRSIZE);
lookup[index][1] = g((index+1) * TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE);
where g(q) is 1E6 * f(q/1E6)
2) The reverse lookup assigns an entry in lookup[index][small]
3) This index needs to match the above, i.e.
* if small=0 then
p = (index + 1) * 1000000/TFRC_CALC_X_ARRSIZE
* if small=1 then
p = (index+1) * TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE
These are exactly the changes that the patch makes; previously the code did
not conform to the way the lookup table was generated (this difference resulted
in a mean error of about 1.12%).
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
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This adds documentation for the TCP Reno throughput equation which is at
the heart of the TFRC sending rate / loss rate calculations.
It spells out precisely how the values were determined and what they mean.
The equations were derived through reverse engineering and found to be
fully accurate (verified using test programs).
This patch does not change any code.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
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This reaps the benefit of the earlier patch, which changed the type of
CCID 3 states to use enums, in that many conditions are now simplified
and the number of possible (unexpected) values is greatly reduced.
In a few instances, this also allowed to simplify pre-conditions; where
care has been taken to retain logical equivalence.
[DCCP]: Introduce a consistent BUG/WARN message scheme
This refines the existing set of DCCP messages so that
* BUG(), BUG_ON(), WARN_ON() have meaningful DCCP-specific counterparts
* DCCP_CRIT (for severe warnings) is not rate-limited
* DCCP_WARN() is introduced as rate-limited wrapper
Using these allows a faster and cleaner transition to their original
counterparts once the code has matured into a full DCCP implementation.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
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Just updating copyright and contacts
Signed off by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Signed-off-by: Jörn Engel <joern@wohnheim.fh-wedel.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
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A bunch of asm/bug.h includes are both not needed (since it will get
pulled anyway) and bogus (since they are done too early). Removed.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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