dccp: Set per-connection CCIDs via socket options

With this patch, TX/RX CCIDs can now be changed on a per-connection basis, which
overrides the defaults set by the global sysctl variables for TX/RX CCIDs.

To make full use of this facility, the remaining patches of this patch set are
needed, which track dependencies and activate negotiated feature values.

Note on the maximum number of CCIDs that can be registered:
-----------------------------------------------------------
The maximum number of CCIDs that can be registered on the socket is constrained
by the space in a Confirm/Change feature negotiation option. 

The space in these in turn depends on the size of header options as defined
in RFC 4340, 5.8. Since this is a recurring constant, it has been moved from
ackvec.h into linux/dccp.h, clarifying its purpose.

Relative to this size, the maximum number of CCID identifiers that can be 
present in a Confirm option (which always consumes 1 byte more than a Change
option, cf. 6.1) is 2 bytes less than the maximum TLV size: one for the
CCID-feature-type and one for the selected value.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/dccp.h b/include/linux/dccp.h
index eda389ce04f4..6a72ff52a8a4 100644
--- a/include/linux/dccp.h
+++ b/include/linux/dccp.h
@@ -168,6 +168,8 @@ enum {
         DCCPO_MIN_CCID_SPECIFIC = 128,
         DCCPO_MAX_CCID_SPECIFIC = 255,
 };
+/* maximum size of a single TLV-encoded DCCP option (sans type/len bytes) */
+#define DCCP_SINGLE_OPT_MAXLEN  253
 
 /* DCCP CCIDS */
 enum {
@@ -203,6 +205,9 @@ enum dccp_feature_numbers {
 #define DCCP_SOCKOPT_SEND_CSCOV         10
 #define DCCP_SOCKOPT_RECV_CSCOV         11
 #define DCCP_SOCKOPT_AVAILABLE_CCIDS    12
+#define DCCP_SOCKOPT_CCID               13
+#define DCCP_SOCKOPT_TX_CCID            14
+#define DCCP_SOCKOPT_RX_CCID            15
 #define DCCP_SOCKOPT_CCID_RX_INFO       128
 #define DCCP_SOCKOPT_CCID_TX_INFO       192