dccp: Implement lookup table for feature-negotiation information

A lookup table for feature-negotiation information, extracted from RFC
4340/42, is provided by this patch. All currently known features can
be found in this table, along with their feature location, their
default value, and type.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/dccp.h

@@ -176,19 +176,20 @@ enum {
 };
 
 /* DCCP features (RFC 4340 section 6.4) */
-enum {
+enum dccp_feature_numbers {
 	DCCPF_RESERVED = 0,
 	DCCPF_CCID = 1,
-	DCCPF_SHORT_SEQNOS = 2,		/* XXX: not yet implemented */
+	DCCPF_SHORT_SEQNOS = 2,
 	DCCPF_SEQUENCE_WINDOW = 3,
-	DCCPF_ECN_INCAPABLE = 4,	/* XXX: not yet implemented */
+	DCCPF_ECN_INCAPABLE = 4,
 	DCCPF_ACK_RATIO = 5,
 	DCCPF_SEND_ACK_VECTOR = 6,
 	DCCPF_SEND_NDP_COUNT = 7,
 	DCCPF_MIN_CSUM_COVER = 8,
-	DCCPF_DATA_CHECKSUM = 9,	/* XXX: not yet implemented */
+	DCCPF_DATA_CHECKSUM = 9,
 	/* 10-127 reserved */
 	DCCPF_MIN_CCID_SPECIFIC = 128,
+	DCCPF_SEND_LEV_RATE = 192,	/* RFC 4342, sec. 8.4 */
 	DCCPF_MAX_CCID_SPECIFIC = 255,
 };
 

net/dccp/feat.c

@@ -23,6 +23,43 @@
 
 #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)
+
 int dccp_feat_change(struct dccp_minisock *dmsk, u8 type, u8 feature,
 		     u8 *val, u8 len, gfp_t gfp)
 {
@@ -639,6 +676,8 @@ const char *dccp_feat_name(const u8 feat)
 	if (feat > DCCPF_DATA_CHECKSUM && feat < DCCPF_MIN_CCID_SPECIFIC)
 		return feature_names[DCCPF_RESERVED];
 
+	if (feat ==  DCCPF_SEND_LEV_RATE)
+		return "Send Loss Event Rate";
 	if (feat >= DCCPF_MIN_CCID_SPECIFIC)
 		return "CCID-specific";