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dccp: Support for the exchange of NN options in established state

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In contrast to static feature negotiation at the begin of a connection, which
establishes the capabilities of both endpoints, this patch introduces support
for dynamic exchange of feature negotiation options.

Such a dynamic 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
   as the connection progresses".

Both are NN (non-negotiable) features. Hence dynamic feature "negotiation" is
distinguished from static/pre-connection negotiation by the following:
 * no new capabilities are negotiated (those that matter for the connection
   are negotiated prior to setting up the connection, comparable to SIP);
 * features must be understood by each endpoint: as per RFC 4340, 6.4, 
   Sequence Window is "Req'd" and Ack Ratio must be understood when CCID-2
   is used as per the note underneath Table 4.

These characteristics are reflected in the implementation:
 * only NN options can be exchanged after connection setup;
 * NN options are activated directly after validating them. The rationale is
   that a peer must accept every valid NN value (RFC 4340, 6.3.2), hence it
   will either accept the value and send a "Confirm R", or it will send an
   empty Confirm (which will reset the connection according to FN rules). 
 * An Ack is scheduled directly after activation to accelerate communicating
   the update to the peer.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
This commit is contained in:
Gerrit Renker 2008-09-04 07:30:19 +02:00
parent 76f738a795
commit 624a965a93
2 changed files with 58 additions and 0 deletions
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1
net/dccp/dccp.h
View File

@ -436,6 +436,7 @@ static inline int dccp_ack_pending(const struct sock *sk)
inet_csk_ack_scheduled(sk);
}
extern int dccp_feat_signal_nn_change(struct sock *sk, u8 feat, u64 nn_val);
extern int dccp_feat_finalise_settings(struct dccp_sock *dp);
extern int dccp_feat_server_ccid_dependencies(struct dccp_request_sock *dreq);
extern int dccp_feat_insert_opts(struct dccp_sock*, struct dccp_request_sock*,

57
net/dccp/feat.c
View File

@ -13,6 +13,7 @@
* -----------
* o Feature negotiation is coordinated with connection setup (as in TCP), wild
* changes of parameters of an established connection are not supported.
* o Changing NN values (Ack Ratio only) is supported in state OPEN/PARTOPEN.
* o All currently known SP features have 1-byte quantities. If in the future
* extensions of RFCs 4340..42 define features with item lengths larger than
* one byte, a feature-specific extension of the code will be required.
@ -337,6 +338,20 @@ static int __dccp_feat_activate(struct sock *sk, const int idx,
return dccp_feat_table[idx].activation_hdlr(sk, val, rx);
}
/**
* dccp_feat_activate - Activate feature value on socket
* @sk: fully connected DCCP socket (after handshake is complete)
* @feat_num: feature to activate, one of %dccp_feature_numbers
* @local: whether local (1) or remote (0) @feat_num is meant
* @fval: the value (SP or NN) to activate, or NULL to use the default value
* For general use this function is preferable over __dccp_feat_activate().
*/
static int dccp_feat_activate(struct sock *sk, u8 feat_num, bool local,
dccp_feat_val const *fval)
{
return __dccp_feat_activate(sk, dccp_feat_index(feat_num), local, fval);
}
/* Test for "Req'd" feature (RFC 4340, 6.4) */
static inline int dccp_feat_must_be_understood(u8 feat_num)
{
@ -734,6 +749,48 @@ int dccp_feat_register_nn(struct sock *sk, u8 feat, u64 val)
return __feat_register_nn(&dccp_sk(sk)->dccps_featneg, feat, 0, val);
}
/**
* dccp_feat_signal_nn_change - Update NN values for an established connection
* @sk: DCCP socket of an established connection
* @feat: NN feature number from %dccp_feature_numbers
* @nn_val: the new value to use
* This function is used to communicate NN updates out-of-band. The difference
* to feature negotiation during connection setup is that values are activated
* immediately after validation, i.e. we don't wait for the Confirm: either the
* value is accepted by the peer (and then the waiting is futile), or it is not
* (Reset or empty Confirm). We don't accept empty Confirms - transmitted values
* are validated, and the peer "MUST accept any valid value" (RFC 4340, 6.3.2).
*/
int dccp_feat_signal_nn_change(struct sock *sk, u8 feat, u64 nn_val)
{
struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
dccp_feat_val fval = { .nn = nn_val };
struct dccp_feat_entry *entry;
if (sk->sk_state != DCCP_OPEN && sk->sk_state != DCCP_PARTOPEN)
return 0;
if (dccp_feat_type(feat) != FEAT_NN ||
!dccp_feat_is_valid_nn_val(feat, nn_val))
return -EINVAL;
entry = dccp_feat_list_lookup(fn, feat, 1);
if (entry != NULL) {
dccp_pr_debug("Ignoring %llu, entry %llu exists in state %s\n",
(unsigned long long)nn_val,
(unsigned long long)entry->val.nn,
dccp_feat_sname[entry->state]);
return 0;
}
if (dccp_feat_activate(sk, feat, 1, &fval))
return -EADV;
inet_csk_schedule_ack(sk);
return dccp_feat_push_change(fn, feat, 1, 0, &fval);
}
EXPORT_SYMBOL_GPL(dccp_feat_signal_nn_change);
/*
* Tracking features whose value depend on the choice of CCID
*