dccp: Policy-based packet dequeueing infrastructure

This patch adds a generic infrastructure for policy-based dequeueing of 
TX packets and provides two policies:
 * a simple FIFO policy (which is the default) and
 * a priority based policy (set via socket options).
Both policies honour the tx_qlen sysctl for the maximum size of the write
queue (can be overridden via socket options). 

The priority policy uses skb->priority internally to assign an u32 priority
identifier, using the same ranking as SO_PRIORITY. The skb->priority field
is set to 0 when the packet leaves DCCP. The priority is supplied as ancillary
data using cmsg(3), the patch also provides the requisite parsing routines.

Signed-off-by: Tomasz Grobelny <tomasz@grobelny.oswiecenia.net>
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>

1 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/dccp.h b/include/linux/dccp.h
index eed52bcd35d0..010e2d87ed75 100644
--- a/include/linux/dccp.h
+++ b/include/linux/dccp.h
@@ -197,6 +197,21 @@ enum dccp_feature_numbers {
         DCCPF_MAX_CCID_SPECIFIC = 255,
 };
 
+/* DCCP socket control message types for cmsg */
+enum dccp_cmsg_type {
+        DCCP_SCM_PRIORITY = 1,
+        DCCP_SCM_QPOLICY_MAX = 0xFFFF,
+        /* ^-- Up to here reserved exclusively for qpolicy parameters */
+        DCCP_SCM_MAX
+};
+
+/* DCCP priorities for outgoing/queued packets */
+enum dccp_packet_dequeueing_policy {
+        DCCPQ_POLICY_SIMPLE,
+        DCCPQ_POLICY_PRIO,
+        DCCPQ_POLICY_MAX
+};
+
 /* DCCP socket options */
 #define DCCP_SOCKOPT_PACKET_SIZE        1 /* XXX deprecated, without effect */
 #define DCCP_SOCKOPT_SERVICE            2
@@ -210,6 +225,8 @@ enum dccp_feature_numbers {
 #define DCCP_SOCKOPT_CCID               13
 #define DCCP_SOCKOPT_TX_CCID            14
 #define DCCP_SOCKOPT_RX_CCID            15
+#define DCCP_SOCKOPT_QPOLICY_ID         16
+#define DCCP_SOCKOPT_QPOLICY_TXQLEN     17
 #define DCCP_SOCKOPT_CCID_RX_INFO       128
 #define DCCP_SOCKOPT_CCID_TX_INFO       192
 
@@ -458,6 +475,8 @@ struct dccp_ackvec;
  * @dccps_hc_rx_ccid - CCID used for the receiver (or receiving half-connection)
  * @dccps_hc_tx_ccid - CCID used for the sender (or sending half-connection)
  * @dccps_options_received - parsed set of retrieved options
+ * @dccps_qpolicy - TX dequeueing policy, one of %dccp_packet_dequeueing_policy
+ * @dccps_tx_qlen - maximum length of the TX queue
  * @dccps_role - role of this sock, one of %dccp_role
  * @dccps_hc_rx_insert_options - receiver wants to add options when acking
  * @dccps_hc_tx_insert_options - sender wants to add options when sending
@@ -500,6 +519,8 @@ struct dccp_sock {
         struct ccid                     *dccps_hc_rx_ccid;
         struct ccid                     *dccps_hc_tx_ccid;
         struct dccp_options_received    dccps_options_received;
+        __u8                            dccps_qpolicy;
+        __u32                           dccps_tx_qlen;
         enum dccp_role                  dccps_role:2;
         __u8                            dccps_hc_rx_insert_options:1;
         __u8                            dccps_hc_tx_insert_options:1;