This patch uupdates the code which registers new packets as received, using the
new circular buffer interface. It contributes a new algorithm which
* supports both tail/head pointers and buffer wrap-around and
* deals with overflow (head/tail move in lock-step).
The updated code is also partioned differently, into
1. dealing with the empty buffer,
2. adding new packets into non-empty buffer,
3. reserving space when encountering a `hole' in the sequence space,
4. updating old state and deciding when old state is irrelevant.
Protection against large burst losses: With regard to (3), it is too costly to
reserve space when there are large bursts of losses. When bursts get too large,
the code does no longer reserve space and just fills in cells normally. This
measure reduces space consumption by a factor of 63.
The code reuses in part the previous implementation by Arnaldo de Melo.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
This provides a routine to consistently update the buffer state when the
peer acknowledges receipt of Ack Vectors; updating state in the list of Ack
Vectors as well as in the circular buffer.
While based on RFC 4340, several additional (and necessary) precautions were
added to protect the consistency of the buffer state. These additions are
essential, since analysis and experience showed that the basic algorithm was
insufficient for this task (which lead to problems that were hard to debug).
The algorithm now
* deals with HC-sender acknowledging to HC-receiver and vice versa,
* keeps track of the last unacknowledged but received seqno in tail_ackno,
* has special cases to reset the overflow condition when appropriate,
* is protected against receiving older information (would mess up buffer state).
Note: The older code performed an unnecessary step, where the sender cleared
Ack Vector state by parsing the Ack Vector received by the HC-receiver. Doing
this was entirely redundant, since
* the receiver always puts the full acknowledgment window (groups 2,3 in 11.4.2)
into the Ack Vectors it sends; hence the HC-receiver is only interested in the
highest state that the HC-sender received;
* this means that the acknowledgment number on the (Data)Ack from the HC-sender
is sufficient; and work done in parsing earlier state is not necessary, since
the later state subsumes the earlier one (see also RFC 4340, A.4).
This older interface (dccp_ackvec_parse()) is therefore removed.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
This completes the implementation of a circular buffer for Ack Vectors, by
extending the current (linear array-based) implementation. The changes are:
(a) An `overflow' flag to deal with the case of overflow. As before, dynamic
growth of the buffer will not be supported; but code will be added to deal
robustly with overflowing Ack Vector buffers.
(b) A `tail_seqno' field. When naively implementing the algorithm of Appendix A
in RFC 4340, problems arise whenever subsequent Ack Vector records overlap,
which can bring the entire run length calculation completely out of synch.
(This is documented on http://www.erg.abdn.ac.uk/users/gerrit/dccp/notes/\
ack_vectors/tracking_tail_ackno/ .)
(c) The buffer lengthi is now computed dynamically (i.e. current fill level),
as the span between head to tail.
As a result, dccp_ackvec_pending() is now simpler - the #ifdef is no longer
necessary since buf_empty is always true when IP_DCCP_ACKVEC is not configured.
Note on overflow handling:
-------------------------
The Ack Vector code previously simply started to drop packets when the
Ack Vector buffer overflowed. This means that the userspace application
will not be able to receive, only because of an Ack Vector storage problem.
Furthermore, overflow may be transient, so that applications may later
recover from the overflow. Recovering from dropped packets is more difficult
(e.g. video key frames).
Hence the patch uses a different policy: when the buffer overflows, the oldest
entries are subsequently overwritten. This has a higher chance of recovery.
Details are on http://www.erg.abdn.ac.uk/users/gerrit/dccp/notes/ack_vectors/
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
This patch
* separates Ack Vector housekeeping code from option-insertion code;
* shifts option-specific code from ackvec.c into options.c;
* introduces a dedicated routine to take care of the Ack Vector records;
* simplifies the dccp_ackvec_insert_avr() routine: the BUG_ON was redundant,
since the list is automatically arranged in descending order of ack_seqno.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
This patch brings the Ack Vector interface up to date. Its main purpose is
to lay the basis for the subsequent patches of this set, which will use the
new data structure fields and routines.
There are no real algorithmic changes, rather an adaptation:
(1) Replaced the static Ack Vector size (2) with a #define so that it can
be adapted (with low loss / Ack Ratio, a value of 1 works, so 2 seems
to be sufficient for the moment) and added a solution so that computing
the ECN nonce will continue to work - even with larger Ack Vectors.
(2) Replaced the #defines for Ack Vector states with a complete enum.
(3) Replaced #defines to compute Ack Vector length and state with general
purpose routines (inlines), and updated code to use these.
(4) Added a `tail' field (conversion to circular buffer in subsequent patch).
(5) Updated the (outdated) documentation for Ack Vector struct.
(6) All sequence number containers now trimmed to 48 bits.
(7) Removal of unused bits:
* removed dccpav_ack_nonce from struct dccp_ackvec, since this is already
redundantly stored in the `dccpavr_ack_nonce' (of Ack Vector record);
* removed Elapsed Time for Ack Vectors (it was nowhere used);
* replaced semantics of dccpavr_sent_len with dccpavr_ack_runlen, since
the code needs to be able to remember the old run length;
* reduced the de-/allocation routines (redundant / duplicate tests).
Justification for removing Elapsed Time information [can be removed]:
---------------------------------------------------------------------
1. The Elapsed Time information for Ack Vectors was nowhere used in the code.
2. DCCP does not implement rate-based pacing of acknowledgments. The only
recommendation for always including Elapsed Time is in section 11.3 of
RFC 4340: "Receivers that rate-pace acknowledgements SHOULD [...]
include Elapsed Time options". But such is not the case here.
3. It does not really improve estimation accuracy. The Elapsed Time field only
records the time between the arrival of the last acknowledgeable packet and
the time the Ack Vector is sent out. Since Linux does not (yet) implement
delayed Acks, the time difference will typically be small, since often the
arrival of a data packet triggers sending feedback at the HC-receiver.
Justification for changes in de-/allocation routines [can be removed]:
----------------------------------------------------------------------
* INIT_LIST_HEAD in dccp_ackvec_record_new was redundant, since the list
pointers were later overwritten when the node was added via list_add();
* dccp_ackvec_record_new() was called in a single place only;
* calls to list_del_init() before calling dccp_ackvec_record_delete() were
redundant, since subsequently the entire element was k-freed;
* since all calls to dccp_ackvec_record_delete() were preceded to a call to
list_del_init(), the WARN_ON test would never evaluate to true;
* since all calls to dccp_ackvec_record_delete() were made from within
list_for_each_entry_safe(), the test for avr == NULL was redundant;
* list_empty() in ackvec_free was redundant, since the same condition is
embedded in the loop condition of the subsequent list_for_each_entry_safe().
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
With this patch, TX/RX CCIDs can now be changed on a per-connection basis, which
overrides the defaults set by the global sysctl variables for TX/RX CCIDs.
To make full use of this facility, the remaining patches of this patch set are
needed, which track dependencies and activate negotiated feature values.
Note on the maximum number of CCIDs that can be registered:
-----------------------------------------------------------
The maximum number of CCIDs that can be registered on the socket is constrained
by the space in a Confirm/Change feature negotiation option.
The space in these in turn depends on the size of header options as defined
in RFC 4340, 5.8. Since this is a recurring constant, it has been moved from
ackvec.h into linux/dccp.h, clarifying its purpose.
Relative to this size, the maximum number of CCID identifiers that can be
present in a Confirm option (which always consumes 1 byte more than a Change
option, cf. 6.1) is 2 bytes less than the maximum TLV size: one for the
CCID-feature-type and one for the selected value.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
This patch fixes the following sparse warnings:
* nested min(max()) expression:
net/dccp/ccids/ccid3.c:91:21: warning: symbol '__x' shadows an earlier one
net/dccp/ccids/ccid3.c:91:21: warning: symbol '__y' shadows an earlier one
* Declaration of function prototypes in .c instead of .h file, resulting in
"should it be static?" warnings.
* Declared "struct dccpw" static (local to dccp_probe).
* Disabled dccp_delayed_ack() - not fully removed due to RFC 4340, 11.3
("Receivers SHOULD implement delayed acknowledgement timers ...").
* Used a different local variable name to avoid
net/dccp/ackvec.c:293:13: warning: symbol 'state' shadows an earlier one
net/dccp/ackvec.c:238:33: originally declared here
* Removed unused functions `dccp_ackvector_print' and `dccp_ackvec_print'.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
This is reduces the length of the struct ackvec/ackvec_record fields. It is
a purely text-based replacement:
s#dccpavr_#avr_#g;
s#dccpav_#av_#g;
and increases readability somewhat.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Hopefully captured all single statement cases under net/. I'm
not too sure if there is some policy about #includes that are
"guaranteed" (ie., in the current tree) to be available through
some other #included header, so I just added linux/kernel.h to
each changed file that didn't #include it previously.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
Slab destructors were no longer supported after Christoph's
c59def9f22 change. They've been
BUGs for both slab and slub, and slob never supported them
either.
This rips out support for the dtor pointer from kmem_cache_create()
completely and fixes up every single callsite in the kernel (there were
about 224, not including the slab allocator definitions themselves,
or the documentation references).
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
This patch
* organizes the sequence arithmetic functions into one corner of dccp.h
* performs a small modification of dccp_set_seqno to make it more widely reusable
(now it is safe to use any number, since it performs modulo-2^48 assignment)
* adds functions and generic macros for 48-bit sequence arithmetic:
--48 bit complement
--modulo-48 addition and modulo-48 subtraction
--dccp_inc_seqno now a special case of add48
Constants renamed following a suggestion by Arnaldo.
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@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
That accumulated over the last months hackaton, shame on me for not
using git-apply whitespace helping hand, will do that from now on.
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Replace all uses of kmem_cache_t with struct kmem_cache.
The patch was generated using the following script:
#!/bin/sh
#
# Replace one string by another in all the kernel sources.
#
set -e
for file in `find * -name "*.c" -o -name "*.h"|xargs grep -l $1`; do
quilt add $file
sed -e "1,\$s/$1/$2/g" $file >/tmp/$$
mv /tmp/$$ $file
quilt refresh
done
The script was run like this
sh replace kmem_cache_t "struct kmem_cache"
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Ack vectors grow proportional to the window size. If an ack vector does not fit
into a single option, it must be spread across multiple options. This patch
will allow for windows to grow larger.
Committer note: Simplified the patch a bit, original algorithm kept.
Signed-off-by: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Commiter note:
This was split from Andrea's original patch, in the process I changed the type
of the ackvec index fields to u16 instead of to int and haven't folded
dccp_ackvec_parse with dccp_ackvec_check_rcv_ackno.
Next patch will actually do the insertion of more than one ackvec per packet,
using, initially, up to a max of 2 ackvecs as per Andrea's original patch, then
I'll work on support for larger ackvecs, be it using a sysctl or using
setsockopt.
Signed-off-by: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Commiter note: original patch was splitted.
Signed-off-by: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
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>
This patch
* makes debugging (when configured) work both for static / module build
* provides generic debugging macros for use in other DCCP / CCID modules
* adds missing information about debug parameters to Kconfig
* performs some code tidy-up
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Do not traverse the list of ack vector records [proportional to window size]
when we know we will not find what we are looking for. This is especially
useful because ack vectors are checked twice:
1) Upon parsing of options.
2) Upon notification of a new ack.
All of the work will occur during check #1. Therefore, when check #2 is
performed, no new work will be done. This is now "detected" and there is no
performance hit when doing #2.
Signed-off-by: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
This patch does not change code; it performs some trivial clean/tidy-ups:
* removal of a `debug_prefix' string in favour of the
already existing dccp_role(sk)
* add documentation of structures and constants
* separated out the cases for invalid packets (step 1
of the packet validation)
* removing duplicate statements
* combining declaration & initialisation
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Updates the references to spec documents throughout the code, taking into
account that
* the DCCP, CCID 2, and CCID 3 drafts all became RFCs in March this year
* RFC 1063 was obsoleted by RFC 1191
* draft-ietf-tcpimpl-pmtud-0x.txt was published as an Informational
RFC, RFC 2923 on 2000-09-22.
All references verified.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Get rid of unused variables in ackvector state.
Signed-off-by: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Fix the way state is masked out. DCCP_ACKVEC_STATE_NOT_RECEIVED is
defined as appears in the packet, therefore bit shifting is not
required. This fix allows CCID2 to correctly detect losses.
Signed-off-by: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Fix ackvector length calculation upon receiving an "ack-of-ack". This
patch avoids the ackvector from growing too large which causes it to
not be inserted into packets.
Signed-off-by: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
A soft lockup existed in the handling of ack vector records.
Specifically, when a tail of the list of ack vector records was
removed, it was possible to end up iterating infinitely on an element
of the tail.
Signed-off-by: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: David S. Miller <davem@davemloft.net>
And not the silly LIMIT_NETDEBUG and silently return without inserting
the option requested.
Also drop some old debugging messages associated to option insertion.
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Based on a patch by Andrea Bittau.
Signed-off-by: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Simplifying the code a bit as we're always using DCCP_MAX_ACKVEC_LEN.
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
- added typedef unsigned int __nocast gfp_t;
- replaced __nocast uses for gfp flags with gfp_t - it gives exactly
the same warnings as far as sparse is concerned, doesn't change
generated code (from gcc point of view we replaced unsigned int with
typedef) and documents what's going on far better.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Isolating it, that will be used when we introduce a CCID2 (TCP-Like)
implementation.
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
