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linux/net/dccp/feat.h
Gerrit Renker d6916f87ca dccp: support for the exchange of NN options in established state 1/2 
In contrast to static feature negotiation at the begin of a connection, this
patch introduces support for exchange of dynamically changing options.

Such an update/exchange is necessary in at least two cases:
 * CCID-2's Ack Ratio (RFC 4341, 6.1.2) which changes during the connection;
 * Sequence Window values that, as per RFC 4340, 7.5.2, should be sent "as
   the connection progresses".

Both are non-negotiable (NN) features, which means that no new capabilities
are negotiated, but rather that changes in known parameters are brought
up-to-date at either end.

Thse characteristics are reflected by the implementation:
 * only NN options can be exchanged after connection setup;
 * an ack is scheduled directly after activation to speed up the update;
 * CCIDs may request changes to an NN feature even if a negotiation for that
   feature is already underway: this is required by CCID-2, where changes in
   cwnd necessitate Ack Ratio changes, such that the previous Ack Ratio (which
   is still being negotiated) would cause irrecoverable RTO timeouts (thanks
   to work by Samuel Jero).	   

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Samuel Jero <sj323707@ohio.edu>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.uk>
2011-08-01 07:52:34 -06:00

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#ifndef _DCCP_FEAT_H
#define _DCCP_FEAT_H
/*
* net/dccp/feat.h
*
* Feature negotiation for the DCCP protocol (RFC 4340, section 6)
* Copyright (c) 2008 Gerrit Renker <gerrit@erg.abdn.ac.uk>
* Copyright (c) 2005 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/types.h>
#include "dccp.h"
/*
* Known limit values
*/
/* Ack Ratio takes 2-byte integer values (11.3) */
#define DCCPF_ACK_RATIO_MAX 0xFFFF
/* Wmin=32 and Wmax=2^46-1 from 7.5.2 */
#define DCCPF_SEQ_WMIN 32
#define DCCPF_SEQ_WMAX 0x3FFFFFFFFFFFull
/* Maximum number of SP values that fit in a single (Confirm) option */
#define DCCP_FEAT_MAX_SP_VALS (DCCP_SINGLE_OPT_MAXLEN - 2)
enum dccp_feat_type {
FEAT_AT_RX = 1, /* located at RX side of half-connection */
FEAT_AT_TX = 2, /* located at TX side of half-connection */
FEAT_SP = 4, /* server-priority reconciliation (6.3.1) */
FEAT_NN = 8, /* non-negotiable reconciliation (6.3.2) */
FEAT_UNKNOWN = 0xFF /* not understood or invalid feature */
};
enum dccp_feat_state {
FEAT_DEFAULT = 0, /* using default values from 6.4 */
FEAT_INITIALISING, /* feature is being initialised */
FEAT_CHANGING, /* Change sent but not confirmed yet */
FEAT_UNSTABLE, /* local modification in state CHANGING */
FEAT_STABLE /* both ends (think they) agree */
};
/**
* dccp_feat_val - Container for SP or NN feature values
* @nn: single NN value
* @sp.vec: single SP value plus optional preference list
* @sp.len: length of @sp.vec in bytes
*/
typedef union {
u64 nn;
struct {
u8 *vec;
u8 len;
} sp;
} dccp_feat_val;
/**
* struct feat_entry - Data structure to perform feature negotiation
* @val: feature's current value (SP features may have preference list)
* @state: feature's current state
* @feat_num: one of %dccp_feature_numbers
* @needs_mandatory: whether Mandatory options should be sent
* @needs_confirm: whether to send a Confirm instead of a Change
* @empty_confirm: whether to send an empty Confirm (depends on @needs_confirm)
* @is_local: feature location (1) or feature-remote (0)
* @node: list pointers, entries arranged in FIFO order
*/
struct dccp_feat_entry {
dccp_feat_val val;
enum dccp_feat_state state:8;
u8 feat_num;
bool needs_mandatory,
needs_confirm,
empty_confirm,
is_local;
struct list_head node;
};
static inline u8 dccp_feat_genopt(struct dccp_feat_entry *entry)
{
if (entry->needs_confirm)
return entry->is_local ? DCCPO_CONFIRM_L : DCCPO_CONFIRM_R;
return entry->is_local ? DCCPO_CHANGE_L : DCCPO_CHANGE_R;
}
/**
* struct ccid_dependency - Track changes resulting from choosing a CCID
* @dependent_feat: one of %dccp_feature_numbers
* @is_local: local (1) or remote (0) @dependent_feat
* @is_mandatory: whether presence of @dependent_feat is mission-critical or not
* @val: corresponding default value for @dependent_feat (u8 is sufficient here)
*/
struct ccid_dependency {
u8 dependent_feat;
bool is_local:1,
is_mandatory:1;
u8 val;
};
/*
* Sysctls to seed defaults for feature negotiation
*/
extern unsigned long sysctl_dccp_sequence_window;
extern int sysctl_dccp_rx_ccid;
extern int sysctl_dccp_tx_ccid;
extern int dccp_feat_init(struct sock *sk);
extern void dccp_feat_initialise_sysctls(void);
extern int dccp_feat_register_sp(struct sock *sk, u8 feat, u8 is_local,
u8 const *list, u8 len);
extern int dccp_feat_parse_options(struct sock *, struct dccp_request_sock *,
u8 mand, u8 opt, u8 feat, u8 *val, u8 len);
extern int dccp_feat_clone_list(struct list_head const *, struct list_head *);
/*
* Encoding variable-length options and their maximum length.
*
* This affects NN options (SP options are all u8) and other variable-length
* options (see table 3 in RFC 4340). The limit is currently given the Sequence
* Window NN value (sec. 7.5.2) and the NDP count (sec. 7.7) option, all other
* options consume less than 6 bytes (timestamps are 4 bytes).
* When updating this constant (e.g. due to new internet drafts / RFCs), make
* sure that you also update all code which refers to it.
*/
#define DCCP_OPTVAL_MAXLEN 6
extern void dccp_encode_value_var(const u64 value, u8 *to, const u8 len);
extern u64 dccp_decode_value_var(const u8 *bf, const u8 len);
extern u64 dccp_feat_nn_get(struct sock *sk, u8 feat);
extern int dccp_insert_option_mandatory(struct sk_buff *skb);
extern int dccp_insert_fn_opt(struct sk_buff *skb, u8 type, u8 feat,
u8 *val, u8 len, bool repeat_first);
#endif /* _DCCP_FEAT_H */
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