[DCCP]: Basic data structure for feature negotiation
For implementing an improved DCCP 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 a 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 (when cloning from listening socket onto request socket).
I am wondering whether struct list_head is `too fat' for a request socket, but have kept this
structure since it lead to simpler code. If structure sizes are an issue, I'd be willing to
convert to singly-linked list later if necessary (but it would need a tail pointer).
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@xxxxxxxxxxxxxx>
---
net/dccp/feat.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++
net/dccp/feat.h | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 110 insertions(+)
--- 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);
--- a/net/dccp/feat.c
+++ b/net/dccp/feat.c
@@ -23,6 +23,56 @@
#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;
+}
+
+static void dccp_feat_val_destructor(u8 feat_num, dccp_feat_val *val)
+{
+ if (val && dccp_feat_type(feat_num) == FEAT_SP)
+ kfree(val->sp.vec);
+}
+
+static struct dccp_feat_entry *
+ dccp_feat_clone_entry(struct dccp_feat_entry const *original)
+{
+ struct dccp_feat_entry *new;
+ u8 type = dccp_feat_type(original->feat_num);
+
+ if (type == FEAT_UNKNOWN)
+ return NULL;
+
+ new = kmemdup(original, sizeof(struct dccp_feat_entry), gfp_any());
+ if (new == NULL)
+ return NULL;
+
+ if (type == FEAT_SP && dccp_feat_clone_sp_val(&new->val,
+ original->val.sp.vec,
+ original->val.sp.len)) {
+ kfree(new);
+ return NULL;
+ }
+ return new;
+}
+
+static void dccp_feat_entry_destructor(struct dccp_feat_entry *entry)
+{
+ if (entry != NULL) {
+ dccp_feat_val_destructor(entry->feat_num, &entry->val);
+ kfree(entry);
+ }
+}
+
int dccp_feat_change(struct dccp_minisock *dmsk, u8 type, u8 feature,
u8 *val, u8 len, gfp_t gfp)
{
-
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