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).

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>

2 files changed, 74 insertions, 0 deletions

diff --git a/net/dccp/feat.c b/net/dccp/feat.c
index 933a0ecf8d46..94a81b8e5efb 100644
--- a/net/dccp/feat.c
+++ b/net/dccp/feat.c
@@ -23,6 +23,20 @@
 
 #define DCCP_FEAT_SP_NOAGREE (-123)
 
+/* 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 = kmemdup(val, len, gfp_any());
+                if (fval->sp.vec == NULL) {
+                        fval->sp.len = 0;
+                        return -ENOBUFS;
+                }
+        }
+        return 0;
+}
+
 int dccp_feat_change(struct dccp_minisock *dmsk, u8 type, u8 feature,
                      u8 *val, u8 len, gfp_t gfp)
 {
diff --git a/net/dccp/feat.h b/net/dccp/feat.h
index e272222c7ace..94203c230c65 100644
--- a/net/dccp/feat.h
+++ b/net/dccp/feat.h
@@ -14,6 +14,66 @@
 #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
+ * @feat_num: one of %dccp_feature_numbers
+ * @val: feature's current value (SP features may have preference list)
+ * @state: feature's current state
+ * @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 {
+        u8                      feat_num;
+        dccp_feat_val           val;
+        enum dccp_feat_state    state:8;
+        bool                    needs_mandatory:1,
+                                needs_confirm:1,
+                                empty_confirm:1,
+                                is_local:1;
+
+        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);