dccp: Preference list reconciliation

This provides two functions to
 * reconcile preference lists (with appropriate return codes) and
 * reorder the preference list if successful reconciliation changed the
   preferred value.

The patch also removes the old code for processing SP/NN Change options, since
new code to process these is mostly there already; related references have been
commented out.

The code for processing Change options follows in the next patch.

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

1 files changed, 75 insertions, 2 deletions

diff --git a/net/dccp/feat.c b/net/dccp/feat.c
index d90caa7198c3..fe6d557328d6 100644
--- a/net/dccp/feat.c
+++ b/net/dccp/feat.c
@@ -690,6 +690,76 @@ static int dccp_feat_update(struct sock *sk, u8 type, u8 feat, u8 val)
         return 0;
 }
 
+/* Select the first entry in @servlist that also occurs in @clilist (6.3.1) */
+static int dccp_feat_preflist_match(u8 *servlist, u8 slen, u8 *clilist, u8 clen)
+{
+        u8 c, s;
+
+        for (s = 0; s < slen; s++)
+                for (c = 0; c < clen; c++)
+                        if (servlist[s] == clilist[c])
+                                return servlist[s];
+        return -1;
+}
+
+/**
+ * dccp_feat_prefer  -  Move preferred entry to the start of array
+ * Reorder the @array_len elements in @array so that @preferred_value comes
+ * first. Returns >0 to indicate that @preferred_value does occur in @array.
+ */
+static u8 dccp_feat_prefer(u8 preferred_value, u8 *array, u8 array_len)
+{
+        u8 i, does_occur = 0;
+
+        if (array != NULL) {
+                for (i = 0; i < array_len; i++)
+                        if (array[i] == preferred_value) {
+                                array[i] = array[0];
+                                does_occur++;
+                        }
+                if (does_occur)
+                        array[0] = preferred_value;
+        }
+        return does_occur;
+}
+
+/**
+ * dccp_feat_reconcile  -  Reconcile SP preference lists
+ *  @fval: SP list to reconcile into
+ *  @arr: received SP preference list
+ *  @len: length of @arr in bytes
+ *  @is_server: whether this side is the server (and @fv is the server's list)
+ *  @reorder: whether to reorder the list in @fv after reconciling with @arr
+ * When successful, > 0 is returned and the reconciled list is in @fval.
+ * A value of 0 means that negotiation failed (no shared entry).
+ */
+static int dccp_feat_reconcile(dccp_feat_val *fv, u8 *arr, u8 len,
+                               bool is_server, bool reorder)
+{
+        int rc;
+
+        if (!fv->sp.vec || !arr) {
+                DCCP_CRIT("NULL feature value or array");
+                return 0;
+        }
+
+        if (is_server)
+                rc = dccp_feat_preflist_match(fv->sp.vec, fv->sp.len, arr, len);
+        else
+                rc = dccp_feat_preflist_match(arr, len, fv->sp.vec, fv->sp.len);
+
+        if (!reorder)
+                return rc;
+        if (rc < 0)
+                return 0;
+
+        /*
+         * Reorder list: used for activating features and in dccp_insert_fn_opt.
+         */
+        return dccp_feat_prefer(rc, fv->sp.vec, fv->sp.len);
+}
+
+#ifdef __this_is_the_old_framework_and_will_be_removed_later_in_a_subsequent_patch
 static int dccp_feat_reconcile(struct sock *sk, struct dccp_opt_pend *opt,
                                u8 *rpref, u8 rlen)
 {
@@ -885,6 +955,7 @@ static int dccp_feat_nn(struct sock *sk, u8 type, u8 feature, u8 *val, u8 len)
 
         return 0;
 }
+#endif /* (later) */
 
 static void dccp_feat_empty_confirm(struct dccp_minisock *dmsk,
                                     u8 type, u8 feature)
@@ -960,12 +1031,14 @@ int dccp_feat_change_recv(struct sock *sk, u8 type, u8 feature, u8 *val, u8 len)
         switch (feature) {
         /* deal with SP features */
         case DCCPF_CCID:
-                rc = dccp_feat_sp(sk, type, feature, val, len);
+                /* XXX Obsoleted by next patch
+                rc = dccp_feat_sp(sk, type, feature, val, len); */
                 break;
 
         /* deal with NN features */
         case DCCPF_ACK_RATIO:
-                rc = dccp_feat_nn(sk, type, feature, val, len);
+                /* XXX Obsoleted by next patch
+                rc = dccp_feat_nn(sk, type, feature, val, len); */
                 break;
 
         /* XXX implement other features */