Commit bd012f2e authored by Gerrit Renker's avatar Gerrit Renker Committed by David S. Miller
Browse files

dccp: Basic data structure for feature negotiation 



This patch prepares for the new and extended feature-negotiation
routines.

The following feature-negotiation data structures are provided:
	* a container for the various (SP or NN) values,
	* symbolic state names to track feature states,
	* an entry struct which holds all current information together,
	* elementary functions to fill in and process these structures.

Entry structs are arranged as FIFO for the following reason: RFC 4340
specifies that if multiple options of the same type are present, they
are processed in the order of their appearance in the packet; which
means that this order needs to be preserved in the local data
structure (the later insertion code also respects this order).

The struct list_head has been chosen for the following reasons: the most
frequent operations are

 * add new entry at tail (when receiving Change or setting socket
   options);
 * delete entry (when Confirm has been received);
 * deep copy of entire list (cloning from listening socket onto
   request socket).

The NN value has been set to 64 bit, which is a currently sufficient
upper limit (Sequence Window feature has 48 bit).

Thanks to Arnaldo, who contributed the streamlined layout of the entry
struct.

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d5f64238

net/dccp/feat.h

+61 −0
Original line number Diff line number Diff line
@@ -14,6 +14,67 @@ 
#include <linux/types.h>

#include "dccp.h"



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;

}



#ifdef CONFIG_IP_DCCP_DEBUG

extern const char *dccp_feat_typename(const u8 type);

extern const char *dccp_feat_name(const u8 feat);

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