path: root/net/dccp/feat.c

/*
 *  net/dccp/feat.c
 *
 *  An implementation of the DCCP protocol
 *  Andrea Bittau <a.bittau@cs.ucl.ac.uk>
 *
 *  ASSUMPTIONS
 *  -----------
 *  o Feature negotiation is coordinated with connection setup (as in TCP), wild
 *    changes of parameters of an established connection are not supported.
 *  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.
 *
 *  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.
 */

#include <linux/module.h>

#include "ccid.h"
#include "feat.h"

#define DCCP_FEAT_SP_NOAGREE (-123)

static const struct {
	u8			feat_num;		/* DCCPF_xxx */
	enum dccp_feat_type	rxtx;			/* RX or TX  */
	enum dccp_feat_type	reconciliation;		/* SP or NN  */
	u8			default_value;		/* as in 6.4 */
/*
 *    Lookup table for location and type of features (from RFC 4340/4342)
 *  +--------------------------+----+-----+----+----+---------+-----------+
 *  | Feature                  | Location | Reconc. | Initial |  Section  |
 *  |                          | RX | TX  | SP | NN |  Value  | Reference |
 *  +--------------------------+----+-----+----+----+---------+-----------+
 *  | DCCPF_CCID               |    |  X  | X  |    |   2     | 10        |
 *  | DCCPF_SHORT_SEQNOS       |    |  X  | X  |    |   0     |  7.6.1    |
 *  | DCCPF_SEQUENCE_WINDOW    |    |  X  |    | X  | 100     |  7.5.2    |
 *  | DCCPF_ECN_INCAPABLE      | X  |     | X  |    |   0     | 12.1      |
 *  | DCCPF_ACK_RATIO          |    |  X  |    | X  |   2     | 11.3      |
 *  | DCCPF_SEND_ACK_VECTOR    | X  |     | X  |    |   0     | 11.5      |
 *  | DCCPF_SEND_NDP_COUNT     |    |  X  | X  |    |   0     |  7.7.2    |
 *  | DCCPF_MIN_CSUM_COVER     | X  |     | X  |    |   0     |  9.2.1    |
 *  | DCCPF_DATA_CHECKSUM      | X  |     | X  |    |   0     |  9.3.1    |
 *  | DCCPF_SEND_LEV_RATE      | X  |     | X  |    |   0     | 4342/8.4  |
 *  +--------------------------+----+-----+----+----+---------+-----------+
 */
} dccp_feat_table[] = {
	{ DCCPF_CCID,		 FEAT_AT_TX, FEAT_SP, 2 },
	{ DCCPF_SHORT_SEQNOS,	 FEAT_AT_TX, FEAT_SP, 0 },
	{ DCCPF_SEQUENCE_WINDOW, FEAT_AT_TX, FEAT_NN, 100 },
	{ DCCPF_ECN_INCAPABLE,	 FEAT_AT_RX, FEAT_SP, 0 },
	{ DCCPF_ACK_RATIO,	 FEAT_AT_TX, FEAT_NN, 2 },
	{ DCCPF_SEND_ACK_VECTOR, FEAT_AT_RX, FEAT_SP, 0 },
	{ DCCPF_SEND_NDP_COUNT,  FEAT_AT_TX, FEAT_SP, 0 },
	{ DCCPF_MIN_CSUM_COVER,  FEAT_AT_RX, FEAT_SP, 0 },
	{ DCCPF_DATA_CHECKSUM,	 FEAT_AT_RX, FEAT_SP, 0 },
	{ DCCPF_SEND_LEV_RATE,	 FEAT_AT_RX, FEAT_SP, 0 },
};
#define DCCP_FEAT_SUPPORTED_MAX		ARRAY_SIZE(dccp_feat_table)

/**
 * dccp_feat_index  -  Hash function to map feature number into array position
 * Returns consecutive array index or -1 if the feature is not understood.
 */
static int dccp_feat_index(u8 feat_num)
{
	/* The first 9 entries are occupied by the types from RFC 4340, 6.4 */
	if (feat_num > DCCPF_RESERVED && feat_num <= DCCPF_DATA_CHECKSUM)
		return feat_num - 1;

	/*
	 * Other features: add cases for new feature types here after adding
	 * them to the above table.
	 */
	switch (feat_num) {
	case DCCPF_SEND_LEV_RATE:
			return DCCP_FEAT_SUPPORTED_MAX - 1;
	}
	return -1;
}

static u8 dccp_feat_type(u8 feat_num)
{
	int idx = dccp_feat_index(feat_num);

	if (idx < 0)
		return FEAT_UNKNOWN;
	return dccp_feat_table[idx].reconciliation;
}

static int dccp_feat_default_value(u8 feat_num)
{
	int idx = dccp_feat_index(feat_num);
	/*
	 * There are no default values for unknown features, so encountering a
	 * negative index here indicates a serious problem somewhere else.
	 */
	DCCP_BUG_ON(idx < 0);

	return idx < 0 ? 0 : dccp_feat_table[idx].default_value;
}

/* copy constructor, fval must not already contain allocated memory */
static int dccp_feat_clone_sp_val(dccp_feat_val *fval, u8 const *val, u8 len)
{
	fval->sp.len = len;
	if (fval->sp.len > 0) {
		fval->sp.vec