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: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

as it accentally contained the wrong set of patches. These will be
submitted separately.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This implements [RFC 3448, 4.5], which performs congestion avoidance behaviour
by reducing the transmit rate as the queueing delay (measured in terms of
long-term RTT) increases.

Oscillation can be turned on/off via a module option (do_osc_prev) and via sysfs
(using mode 0644), the default is off.

Overflow analysis:
------------------
 * oscillation prevention is done after update_x(), so that t_ipi <= 64000;
 * hence the multiplication "t_ipi * sqrt(R_sample)" needs 64 bits;
 * done using u64 for sqrt_sample and explicit typecast of t_ipi;
 * the divisor, R_sqmean, is non-zero because oscillation prevention is first
   called when receiving the second feedback packet, and tfrc_scaled_rtt() > 0.

A detailed discussion of the algorithm (with plots) is on
http://www.erg.abdn.ac.uk/users/gerrit/dccp/notes/ccid3/sender_notes/oscillation_prevention/

The algorithm has negative side effects:
  * when allowing to decrease t_ipi (leads to a large RTT) and
  * when using it during slow-start;
both uses are therefore disabled.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This patch is a requirement for enabling ECN support later on. With that change
in mind, the following preparations are done:
 * renamed handle_loss() into congestion_event() since it returns true when a
   congestion event happens (it will eventually also take care of ECN packets);
 * lets tfrc_rx_congestion_event() always update the RX history records, since
   this routine needs to be called for each non-duplicate packet anyway;
 * made all involved boolean-type functions to have return type `bool';

Updating the RX history records is now only necessary for the packets received
up to sending the first feedback. The receiver code becomes again simpler.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This updates the computation of X_recv with regard to Errata 610/611 for
RFC 4342 and draft rfc3448bis-06, ensuring that at least an interval of 1
RTT is used to compute X_recv.  The change is wrapped into a new function
ccid3_hc_rx_x_recv().

Further changes:
----------------
 * feedback is not sent when no data packets arrived (bytes_recv == 0), as per
   rfc3448bis-06, 6.2;
 * take the timestamp for the feedback /after/ dccp_send_ack() returns, to avoid
   taking the transmission time into account (in case layer-2 is busy);
 * clearer handling of failure in ccid3_first_li().
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This improves the receiver RTT sampling algorithm so that it tries harder to get
as many RTT samples as possible. 

The algorithm is based the concepts presented in RFC 4340, 8.1, using timestamps
and the CCVal window counter. There exist 4 cases for the CCVal difference:
 * == 0: less than RTT/4 passed since last packet -- unusable;
 *  > 4: (much) more than 1 RTT has passed since last packet -- also unusable;
 * == 4: perfect sample (exactly one RTT has passed since last packet);
 * 1..3: sub-optimal sample (between RTT/4 and 3*RTT/4 has passed).

In the last case the algorithm tried to optimise by storing away the candidate
and then re-trying next time. The problem is that
 * a large number of samples is needed to smooth out the inaccuracies of the
   algorithm;
 * the sender may not be sending enough packets to warrant a "next time";
 * hence it is better to use suboptimal samples whenever possible.
The algorithm now stores away the current sample only if the difference is 0.

Applicability and background
----------------------------
A realistic example is MP3 streaming where packets are sent at a rate of less
than one packet per RTT, which means that suitable samples are absent for a
very long time.

The effectiveness of using suboptimal samples (with a delta between 1 and 4) was
confirmed by instrumenting the algorithm with counters. The results of two 20
second test runs were:
 * With the old algorithm and a total of 38442 function calls, only 394 of these
   calls resulted in usable RTT samples (about 1%), and 378 out of these were
   "perfect" samples and 28013 (unused) samples had a delta of 1..3.
 * With the new algorithm and a total of 37057 function calls, 1702 usable RTT
   samples were retrieved (about 4.6%), 5 out of these were "perfect" samples.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This updates the CCID-3 receiver in part with regard to errata 610 and 611
(http://www.rfc-editor.org/errata_list.php), which change RFC 4342 to use the
Receive Rate as specified in rfc3448bis, requiring to constantly sample the
RTT (or use a sender RTT).

Doing this requires reusing the RX history structure after dealing with a loss.

The patch does not resolve how to compute X_recv if the interval is less
than 1 RTT. A FIXME has been added (and is resolved in subsequent patch).

Furthermore, since this is all TFRC-based functionality, the RTT estimation
is now also performed by the dccp_tfrc_lib module. This further simplifies
the CCID-3 code.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This migrates more TFRC-related code into the dccp_tfrc_lib:
 * sampling of the packet size `s' (which is only needed until the first
   loss interval is computed (ccid3_first_li));
 * updating the byte-counter `bytes_recvd' in between sending feedbacks.
The result is a better separation of CCID-3 specific and TFRC specific
code, which aids future integration with ECN and e.g. CCID-4.

Further changes:
----------------
 * replaced magic number of 536 with equivalent constant TCP_MIN_RCVMSS;
   (this constant is also used when no estimate for `s' is available).
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This changes the return type of tfrc_lh_update_i_mean() to void, since that 
function returns always `false'. This is due to 

 	len = dccp_delta_seqno(cur->li_seqno, DCCP_SKB_CB(skb)->dccpd_seq) + 1;
 
 	if (len - (s64)cur->li_length <= 0)	/* duplicate or reordered */
		return 0;

which means that update_i_mean can only increase the length of the open loss
interval I_0, and hence the value of I_tot0 (RFC 3448, 5.4). Consequently the
test `i_mean < old_i_mean' at the end of the function always evaluates to false.

There is no known way by which a loss interval can suddenly become shorter,
therefore the return type of the function is changed to void. (That is, under
the given circumstances step (3) in RFC 3448, 6.1 will not occur.)

Further changes:
----------------
 * the function is now called from tfrc_rx_handle_loss, which is equivalent
   to the previous way of calling from rx_packet_recv (it was called whenever
   there was no new or pending loss, now  it is also updated when there is
   a pending loss - this increases the accuracy a bit);
 * added a FIXME to possibly consider NDP counting as per RFC 4342 (this is
   not implemented yet).
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This enables the TFRC code to begin loss detection (as soon as the module
is loaded), using the latest updates from rfc3448bis-06, 6.3.1:

 * when the first data packet(s) are lost or marked, set
 * X_target = s/(2*R) => f(p) = s/(R * X_target) = 2,
 * corresponding to a loss rate of ~ 20.64%.

The handle_loss() function is now called right at the begin of rx_packet_recv()
and thus no longer protected against duplicates: hence a call to rx_duplicate()
has been added.  Such a call makes sense now, as the previous patch initialises
the first entry with a sequence number of GSR.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This patch 
 1) separates history allocation and initialisation, to facilitate early
    loss detection (implemented by a subsequent patch);

 2) removes duplication by using the existing tfrc_rx_hist_purge() if the
    allocation fails. This is now possible, since the initialisation routine
 3) zeroes out the entire history before using it. 
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

In the congestion-avoidance phase a decay of p towards 0 is natural once fewer
losses are encountered. Hence the warning message "p is below resolution" is
not necessary, and thus turned into a debug message by this patch.

The TFRC_SMALLEST_P is needed since in theory p never actually reaches 0. When
no further losses are encountered, the loss interval I_0 grows in length, 
causing p to decrease towards 0, causing X_calc = s/(RTT * f(p)) to increase.

With the given minimum-resolution this congestion avoidance phase stops at some
fixed value, an approximation formula has been added to the documentation.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This adds a function to take care of the following 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 the maximum of 100%;
 * we want 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).

In the last case, the minimum-resolution value of p is returned.

Furthermore, a bug in ccid3_hc_rx_getsockopt is fixed (1/0 was mapped into ~0U),
which now allows to consistently print the scaled p-values as

        printf("Loss Event Rate = %u.%04u %%\n", rx_info.tfrcrx_p / 10000, 
                                                 rx_info.tfrcrx_p % 10000);
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This removes the RTT-sampling function tfrc_tx_hist_rtt(), since

 1. it suffered from complex passing of return values (the return value both
    indicated successful lookup while the value doubled as RTT sample);

 2. when for some odd reason the sample value equalled 0, this triggered a bug
    warning about "bogus Ack", due to the ambiguity of the return value;

 3. on a passive host which has not sent anything the TX history is empty and
    thus will lead to unwanted "bogus Ack" warnings such as
    ccid3_hc_tx_packet_recv: server(e7b7d518): DATAACK with bogus ACK-28197148
    ccid3_hc_tx_packet_recv: server(e7b7d518): DATAACK with bogus ACK-26641606.

The fix is to replace the implicit encoding by performing the steps manually.					       

Furthermore, the "bogus Ack" warning has been removed, since it can actually be
triggered due to several reasons (network reordering, old packet, (3) above),
hence it is not very useful.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

The BUG_ON(w_tot == 0) only holds if there is no more than 1 loss interval in
the loss history. If there is only a single loss interval, the calc_i_mean()
routine need in fact not be called (RFC 3448, 6.3.1). 
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This sets the sysfs permissions so that root can toggle the `debug'
parameter available for nearly every DCCP module. This is useful 
since there are various module inter-dependencies. The debug flag
can now be toggled at runtime using

  echo 1 > /sys/module/dccp/parameters/dccp_debug
  echo 1 > /sys/module/dccp_ccid2/parameters/ccid2_debug
  echo 1 > /sys/module/dccp_ccid3/parameters/ccid3_debug
  echo 1 > /sys/module/dccp_tfrc_lib/parameters/tfrc_debug

The last is not very useful yet, since no code at the moment calls
the tfrc_debug() macro.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

The BUG_ON(w_tot == 0) only holds if there is no more than 1 loss interval in
the loss history. If there is only a single loss interval, the calc_i_mean()
routine need in fact not be called (RFC 3448, 6.3.1). 
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This sets the sysfs permissions so that root can toggle the `debug'
parameter available for nearly every DCCP module. This is useful 
since there are various module inter-dependencies. The debug flag
can now be toggled at runtime using

  echo 1 > /sys/module/dccp/parameters/dccp_debug
  echo 1 > /sys/module/dccp_ccid2/parameters/ccid2_debug
  echo 1 > /sys/module/dccp_ccid3/parameters/ccid3_debug
  echo 1 > /sys/module/dccp_tfrc_lib/parameters/tfrc_debug

The last is not very useful yet, since no code at the moment calls
the tfrc_debug() macro.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This corrects an error in the computation of the open loss interval I_0:
  * the interval length is (highest_seqno - start_seqno) + 1
  * and not (highest_seqno - start_seqno).

This condition was not fully clear in RFC 3448, but reflects the current
revision state of rfc3448bis and is also consistent with RFC 4340, 6.1.1.

Further changes:
----------------
 * variable renamed due to line length constraints;
 * explicit typecast to `s64' to avoid implicit signed/unsigned casting.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This fixes a bug in the logic of the TFRC loss detection:
 * new_loss_indicated() should not be called while a loss is pending;
 * but the code allows this;
 * thus, for two subsequent gaps in the sequence space, when loss_count
   has not yet reached NDUPACK=3, the loss_count is falsely reduced to 1.

To avoid further and similar problems, all loss handling and loss detection is
now done inside tfrc_rx_hist_handle_loss(), using an appropriate routine to
track new losses.

Further changes:
----------------
 * added a reminder that no RX history operations should be performed when
   rx_handle_loss() has identified a (new) loss, since the function takes
   care of packet reordering during loss detection;
 * made tfrc_rx_hist_loss_pending() bool (thanks to an earlier suggestion
   by Arnaldo);		 
 * removed unused functions.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

RFC 4340, 7.7 specifies up to 6 bytes for the NDP Count option, whereas the code
is currently limited to up to 3 bytes. This seems to be a relict of an earlier 
draft version and is brought up to date by the patch.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

The TFRC loss detection code used the wrong loss condition (RFC 4340, 7.7.1):
 * the difference between sequence numbers s1 and s2 instead of 
 * the number of packets missing between s1 and s2 (one less than the distance).

Since this condition appears in many places of the code, it has been put into a
separate function, dccp_loss_free().

Further changes:
----------------
 * tidied up incorrect typing (it was using `int' for u64/s64 types);
 * optimised conditional statements for common case of non-reordered packets;
 * rewrote comments/documentation to match the changes.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

This fixes a bug in computing the inter-packet-interval t_ipi = s/X: 

 scaled_div32(a, b) uses u32 for b, but in "scaled_div32(s, X)" the type of the
 sending rate `X' is u64. Since X is scaled by 2^6, this truncates rates greater
 than 2^26 Bps (~537 Mbps).

Using full 64-bit division now.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>

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: NGerrit 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: NGerrit Renker <gerrit@erg.abdn.ac.uk>

Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This hooks up the TFRC Loss Interval database with CCID 3 packet reception.
In addition, it makes the CCID-specific computation of the first loss
interval (which requires access to all the guts of CCID3) local to ccid3.c.

The patch also fixes an omission in the DCCP code, that of a default /
fallback RTT value (defined in section 3.4 of RFC 4340 as 0.2 sec); while
at it, the  upper bound of 4 seconds for an RTT sample has  been reduced to
match the initial TCP RTO value of 3 seconds from[RFC 1122, 4.2.3.1].
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This moves two inlines back to packet_history.h: these are not private
to packet_history.c, but are needed by CCID3/4 to detect whether a new
loss is indicated, or whether a loss is already pending.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

A ringbuffer-based implementation of loss interval history is easier to
maintain, allocate, and update.

The `swap' routine to keep the RX history sorted is due to and was written
by Arnaldo Carvalho de Melo, simplifying an earlier macro-based variant.

Details:
 * access to the Loss Interval Records via macro wrappers (with safety checks);
 * simplified, on-demand allocation of entries (no extra memory consumption on
   lossless links); cache allocation is local to the module / exported as service;
 * provision of RFC-compliant algorithm to re-compute average loss interval;
 * provision of comprehensive, new loss detection algorithm
 	- support for all cases of loss, including re-ordered/duplicate packets;
 	- waiting for NDUPACK=3 packets to fill the hole;
	- updating loss records when a late-arriving packet fills a hole.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This moves the inlines (which were previously declared as macros) back into
packet_history.h since the loss detection code needs to be able to read entries
from the RX history in order to create the relevant loss entries: it needs at
least tfrc_rx_hist_loss_prev() and tfrc_rx_hist_last_rcv(), which in turn
require the definition of the other inlines (macros).
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This separates RX/TX initialisation and puts all packet history / loss intervals
initialisation into tfrc.c.
The organisation is uniform: slab declaration -> {rx,tx}_init() -> {rx,tx}_exit()
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Moved up the comment "Receiver routines" above the first occurrence of
RX history routines.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Credit here goes to Gerrit Renker, that provided the initial implementation for
this new codebase.

I modified it just to try to make it closer to the existing API, renaming some
functions, add namespacing and fix one bug where the tfrc_rx_hist_alloc was not
freeing the allocated ring entries on the error path.

Original changeset comment from Gerrit:
      -----------
This provides a new, self-contained and generic RX history service for TFRC
based protocols.

Details:
 * new data structure, initialisation and cleanup routines;
 * allocation of dccp_rx_hist entries local to packet_history.c,
   as a service exported by the dccp_tfrc_lib module.
 * interface to automatically track highest-received seqno;
 * receiver-based RTT estimation (needed for instance by RFC 3448, 6.3.1);
 * a generic function to test for `data packets' as per  RFC 4340, sec. 7.7.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This is in preparation for merging the new rx history code written by Gerrit Renker.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This is in preparation for merging the new rx history code written by Gerrit Renker.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch changes the tfrc_lib module in the following manner:

 (1) a dedicated tfrc source file to call the packet history &
     loss interval init/exit functions.
 (2) a dedicated tfrc_pr_debug macro with toggle switch `tfrc_debug'.

Commiter note: renamed tfrc_module.c to tfrc.c, and made CONFIG_IP_DCCP_CCID3
select IP_DCCP_TFRC_LIB.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Based on a previous patch by Gerrit Renker.
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch was based on another made by Gerrit Renker, his changelog was:

    ------------------------------------------------------
The patch set migrates TFRC TX history to a singly-linked list.

The details are:
 * use of a consistent naming scheme (all TFRC functions now begin with `tfrc_');
 * allocation and cleanup are taken care of internally;
 * provision of a lookup function, which is used by the CCID TX infrastructure
   to determine the time a packet was sent (in turn used for RTT sampling);
 * integration of the new interface with the present use in CCID3.
    ------------------------------------------------------

Simplifications I did:

. removing the tfrc_tx_hist_head that had a pointer to the list head and
  another for the slabcache.
. No need for creating a slabcache for each CCID that wants to use the TFRC
  tx history routines, create a single slabcache when the dccp_tfrc_lib module
  init routine is called.
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>