dccp: Mechanism to resolve CCID dependencies

This adds a hook to resolve features whose value depends on the choice of
CCID. It is done at the server since it can only be done after the CCID
values have been negotiated; i.e. the client will add its CCID preference
list on the Change options sent in the Request, which will be reconciled
with the local preference list of the server.

The concept is documented on
http://www.erg.abdn.ac.uk/users/gerrit/dccp/notes/feature_negotiation/\
				implementation_notes.html#ccid_dependencies

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>

diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index 1881527bdcd767eab071725e3bf4351e3bb84258..e656dafb5d96bbdd13e65221d870665f8086cf39 100644 (file)
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -443,6 +443,7 @@ static inline int dccp_ack_pending(const struct sock *sk)
 }
 
 extern int  dccp_feat_finalise_settings(struct dccp_sock *dp);
+extern int  dccp_feat_server_ccid_dependencies(struct dccp_request_sock *dreq);
 extern void dccp_feat_list_purge(struct list_head *fn_list);
 
 extern int dccp_insert_options(struct sock *sk, struct sk_buff *skb);

diff --git a/net/dccp/feat.c b/net/dccp/feat.c
index 4c41441473258597cf148c1c2a0eb828d65b258d..4f86a48723f6738b4116ce273463411a1dba6aa7 100644 (file)
--- a/net/dccp/feat.c
+++ b/net/dccp/feat.c
@@ -166,6 +166,18 @@ static void dccp_feat_entry_destructor(struct dccp_feat_entry *entry)
  * - SP values are always freshly allocated
  * - list is sorted in increasing order of feature number (faster lookup)
  */
+static struct dccp_feat_entry *dccp_feat_list_lookup(struct list_head *fn_list,
+                                                    u8 feat_num, bool is_local)
+{
+       struct dccp_feat_entry *entry;
+
+       list_for_each_entry(entry, fn_list, node)
+               if (entry->feat_num == feat_num && entry->is_local == is_local)
+                       return entry;
+               else if (entry->feat_num > feat_num)
+                       break;
+       return NULL;
+}
 
 /**
  * dccp_feat_entry_new  -  Central list update routine (called by all others)
@@ -560,6 +572,31 @@ int dccp_feat_finalise_settings(struct dccp_sock *dp)
        return 0;
 }
 
+/**
+ * dccp_feat_server_ccid_dependencies  -  Resolve CCID-dependent features
+ * It is the server which resolves the dependencies once the CCID has been
+ * fully negotiated. If no CCID has been negotiated, it uses the default CCID.
+ */
+int dccp_feat_server_ccid_dependencies(struct dccp_request_sock *dreq)
+{
+       struct list_head *fn = &dreq->dreq_featneg;
+       struct dccp_feat_entry *entry;
+       u8 is_local, ccid;
+
+       for (is_local = 0; is_local <= 1; is_local++) {
+               entry = dccp_feat_list_lookup(fn, DCCPF_CCID, is_local);
+
+               if (entry != NULL && !entry->empty_confirm)
+                       ccid = entry->val.sp.vec[0];
+               else
+                       ccid = dccp_feat_default_value(DCCPF_CCID);
+
+               if (dccp_feat_propagate_ccid(fn, ccid, is_local))
+                       return -1;
+       }
+       return 0;
+}
+
 static int dccp_feat_update_ccid(struct sock *sk, u8 type, u8 new_ccid_nr)
 {
        struct dccp_sock *dp = dccp_sk(sk);

diff --git a/net/dccp/output.c b/net/dccp/output.c
index 92f3f6f2ef5132f3321b2f19245746a8e6cc0df2..fea30cdc0bee00af3096859e3c07cb1355c3745e 100644 (file)
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -339,10 +339,12 @@ struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
        DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_RESPONSE;
        DCCP_SKB_CB(skb)->dccpd_seq  = dreq->dreq_iss;
 
-       if (dccp_insert_options_rsk(dreq, skb)) {
-               kfree_skb(skb);
-               return NULL;
-       }
+       /* Resolve feature dependencies resulting from choice of CCID */
+       if (dccp_feat_server_ccid_dependencies(dreq))
+               goto response_failed;
+
+       if (dccp_insert_options_rsk(dreq, skb))
+               goto response_failed;
 
        /* Build and checksum header */
        dh = dccp_zeroed_hdr(skb, dccp_header_size);
@@ -363,6 +365,9 @@ struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
        inet_rsk(req)->acked = 1;
        DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
        return skb;
+response_failed:
+       kfree_skb(skb);
+       return NULL;
 }
 
 EXPORT_SYMBOL_GPL(dccp_make_response);