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linux/net/dccp/ccids/ccid3.h
Gerrit Renker d0995e6a9e dccp ccid-3: Remove dead states 
This patch is thanks to an investigation by Leandro Sales de Melo and his
colleagues. They worked out two state diagrams which highlight the fact that
the xxx_TERM states in CCID-3/4 are in fact not necessary.

And this can be confirmed by in turn looking at the code: the xxx_TERM states
are only ever set in ccid3_hc_{rx,tx}_exit(). These two functions are part
of the following call chain:

 * ccid_hc_{tx,rx}_exit() are called from ccid_delete() only;
 * ccid_delete() invokes ccid_hc_{tx,rx}_exit() in the way of a destructor:
   after calling ccid_hc_{tx,rx}_exit(), the CCID is released from memory;
 * ccid_delete() is in turn called only by ccid_hc_{tx,rx}_delete();
 * ccid_hc_{tx,rx}_delete() is called only if 
   - feature negotiation failed   (dccp_feat_activate_values()),
   - when changing the RX/TX CCID (to eject the current CCID),
   - when destroying the socket   (in dccp_destroy_sock()).

In other words, when CCID-3 sets the state to xxx_TERM, it is at a time where
no more processing should be going on, hence it is not necessary to introduce
a dedicated exit state - this is implicit when unloading the CCID.

The patch removes this state, one switch-statement collapses as a result.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
2008-09-04 07:45:35 +02:00

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/*
* net/dccp/ccids/ccid3.h
*
* Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
* Copyright (c) 2007 The University of Aberdeen, Scotland, UK
*
* An implementation of the DCCP protocol
*
* This code has been developed by the University of Waikato WAND
* research group. For further information please see http://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>
*
* 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.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#ifndef _DCCP_CCID3_H_
#define _DCCP_CCID3_H_
#include <linux/ktime.h>
#include <linux/list.h>
#include <linux/types.h>
#include <linux/tfrc.h>
#include "lib/tfrc.h"
#include "../ccid.h"
/* Two seconds as per RFC 3448 4.2 */
#define TFRC_INITIAL_TIMEOUT (2 * USEC_PER_SEC)
/* Parameter t_mbi from [RFC 3448, 4.3]: backoff interval in seconds */
#define TFRC_T_MBI 64
/*
* The t_delta parameter (RFC 3448, 4.6): delays of less than %USEC_PER_MSEC are
* rounded down to 0, since sk_reset_timer() here uses millisecond granularity.
* Hence we can use a constant t_delta = %USEC_PER_MSEC when HZ >= 500. A coarse
* resolution of HZ < 500 means that the error is below one timer tick (t_gran)
* when using the constant t_delta = t_gran / 2 = %USEC_PER_SEC / (2 * HZ).
*/
#if (HZ >= 500)
# define TFRC_T_DELTA USEC_PER_MSEC
#else
# define TFRC_T_DELTA (USEC_PER_SEC / (2 * HZ))
#warning Coarse CONFIG_HZ resolution -- higher value recommended for TFRC.
#endif
enum ccid3_options {
TFRC_OPT_LOSS_EVENT_RATE = 192,
TFRC_OPT_LOSS_INTERVALS = 193,
TFRC_OPT_RECEIVE_RATE = 194,
};
/* TFRC sender states */
enum ccid3_hc_tx_states {
TFRC_SSTATE_NO_SENT = 1,
TFRC_SSTATE_NO_FBACK,
TFRC_SSTATE_FBACK,
};
/** struct ccid3_hc_tx_sock - CCID3 sender half-connection socket
*
* @x - Current sending rate in 64 * bytes per second
* @x_recv - Receive rate in 64 * bytes per second
* @x_calc - Calculated rate in bytes per second
* @rtt - Estimate of current round trip time in usecs
* @p - Current loss event rate (0-1) scaled by 1000000
* @s - Packet size in bytes
* @t_rto - Nofeedback Timer setting in usecs
* @t_ipi - Interpacket (send) interval (RFC 3448, 4.6) in usecs
* @state - Sender state, one of %ccid3_hc_tx_states
* @last_win_count - Last window counter sent
* @t_last_win_count - Timestamp of earliest packet with
* last_win_count value sent
* @no_feedback_timer - Handle to no feedback timer
* @t_ld - Time last doubled during slow start
* @t_nom - Nominal send time of next packet
* @hist - Packet history
*/
struct ccid3_hc_tx_sock {
u64 x;
u64 x_recv;
u32 x_calc;
u32 rtt;
u32 p;
u32 t_rto;
u32 t_ipi;
u16 s;
enum ccid3_hc_tx_states state:8;
u8 last_win_count;
ktime_t t_last_win_count;
struct timer_list no_feedback_timer;
ktime_t t_ld;
ktime_t t_nom;
struct tfrc_tx_hist_entry *hist;
};
static inline struct ccid3_hc_tx_sock *ccid3_hc_tx_sk(const struct sock *sk)
{
struct ccid3_hc_tx_sock *hctx = ccid_priv(dccp_sk(sk)->dccps_hc_tx_ccid);
BUG_ON(hctx == NULL);
return hctx;
}
/* TFRC receiver states */
enum ccid3_hc_rx_states {
TFRC_RSTATE_NO_DATA = 1,
TFRC_RSTATE_DATA,
};
/** struct ccid3_hc_rx_sock - CCID3 receiver half-connection socket
*
* @last_counter - Tracks window counter (RFC 4342, 8.1)
* @state - Receiver state, one of %ccid3_hc_rx_states
* @bytes_recv - Total sum of DCCP payload bytes
* @x_recv - Receiver estimate of send rate (RFC 3448, sec. 4.3)
* @rtt - Receiver estimate of RTT
* @tstamp_last_feedback - Time at which last feedback was sent
* @hist - Packet history (loss detection + RTT sampling)
* @li_hist - Loss Interval database
* @s - Received packet size in bytes
* @p_inverse - Inverse of Loss Event Rate (RFC 4342, sec. 8.5)
*/
struct ccid3_hc_rx_sock {
u8 last_counter:4;
enum ccid3_hc_rx_states state:8;
u32 bytes_recv;
u32 x_recv;
u32 rtt;
ktime_t tstamp_last_feedback;
struct tfrc_rx_hist hist;
struct tfrc_loss_hist li_hist;
u16 s;
#define p_inverse li_hist.i_mean
};
static inline struct ccid3_hc_rx_sock *ccid3_hc_rx_sk(const struct sock *sk)
{
struct ccid3_hc_rx_sock *hcrx = ccid_priv(dccp_sk(sk)->dccps_hc_rx_ccid);
BUG_ON(hcrx == NULL);
return hcrx;
}
#endif /* _DCCP_CCID3_H_ */
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