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, 64 insertions, 3 deletions

diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 8c125ffab1c..b56efdd2a42 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -189,6 +189,7 @@ int dccp_init_sock(struct sock *sk, const __u8 ctl_sock_initialized)
         dp->dccps_rate_last     = jiffies;
         dp->dccps_role          = DCCP_ROLE_UNDEFINED;
         dp->dccps_service       = DCCP_SERVICE_CODE_IS_ABSENT;
+        dp->dccps_tx_qlen       = sysctl_dccp_tx_qlen;
 
         dccp_init_xmit_timers(sk);
 
@@ -541,6 +542,20 @@ static int do_dccp_setsockopt(struct sock *sk, int level, int optname,
         case DCCP_SOCKOPT_RECV_CSCOV:
                 err = dccp_setsockopt_cscov(sk, val, true);
                 break;
+        case DCCP_SOCKOPT_QPOLICY_ID:
+                if (sk->sk_state != DCCP_CLOSED)
+                        err = -EISCONN;
+                else if (val < 0 || val >= DCCPQ_POLICY_MAX)
+                        err = -EINVAL;
+                else
+                        dp->dccps_qpolicy = val;
+                break;
+        case DCCP_SOCKOPT_QPOLICY_TXQLEN:
+                if (val < 0)
+                        err = -EINVAL;
+                else
+                        dp->dccps_tx_qlen = val;
+                break;
         default:
                 err = -ENOPROTOOPT;
                 break;
@@ -648,6 +663,12 @@ static int do_dccp_getsockopt(struct sock *sk, int level, int optname,
         case DCCP_SOCKOPT_RECV_CSCOV:
                 val = dp->dccps_pcrlen;
                 break;
+        case DCCP_SOCKOPT_QPOLICY_ID:
+                val = dp->dccps_qpolicy;
+                break;
+        case DCCP_SOCKOPT_QPOLICY_TXQLEN:
+                val = dp->dccps_tx_qlen;
+                break;
         case 128 ... 191:
                 return ccid_hc_rx_getsockopt(dp->dccps_hc_rx_ccid, sk, optname,
                                              len, (u32 __user *)optval, optlen);
@@ -690,6 +711,43 @@ int compat_dccp_getsockopt(struct sock *sk, int level, int optname,
 EXPORT_SYMBOL_GPL(compat_dccp_getsockopt);
 #endif
 
+static int dccp_msghdr_parse(struct msghdr *msg, struct sk_buff *skb)
+{
+        struct cmsghdr *cmsg = CMSG_FIRSTHDR(msg);
+
+        /*
+         * Assign an (opaque) qpolicy priority value to skb->priority.
+         *
+         * We are overloading this skb field for use with the qpolicy subystem.
+         * The skb->priority is normally used for the SO_PRIORITY option, which
+         * is initialised from sk_priority. Since the assignment of sk_priority
+         * to skb->priority happens later (on layer 3), we overload this field
+         * for use with queueing priorities as long as the skb is on layer 4.
+         * The default priority value (if nothing is set) is 0.
+         */
+        skb->priority = 0;
+
+        for (; cmsg != NULL; cmsg = CMSG_NXTHDR(msg, cmsg)) {
+
+                if (!CMSG_OK(msg, cmsg))
+                        return -EINVAL;
+
+                if (cmsg->cmsg_level != SOL_DCCP)
+                        continue;
+
+                switch (cmsg->cmsg_type) {
+                case DCCP_SCM_PRIORITY:
+                        if (cmsg->cmsg_len != CMSG_LEN(sizeof(__u32)))
+                                return -EINVAL;
+                        skb->priority = *(__u32 *)CMSG_DATA(cmsg);
+                        break;
+                default:
+                        return -EINVAL;
+                }
+        }
+        return 0;
+}
+
 int dccp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
                  size_t len)
 {
@@ -705,8 +763,7 @@ int dccp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 
         lock_sock(sk);
 
-        if (sysctl_dccp_tx_qlen &&
-            (sk->sk_write_queue.qlen >= sysctl_dccp_tx_qlen)) {
+        if (dccp_qpolicy_full(sk)) {
                 rc = -EAGAIN;
                 goto out_release;
         }
@@ -734,7 +791,11 @@ int dccp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
         if (rc != 0)
                 goto out_discard;
 
-        skb_queue_tail(&sk->sk_write_queue, skb);
+        rc = dccp_msghdr_parse(msg, skb);
+        if (rc != 0)
+                goto out_discard;
+
+        dccp_qpolicy_push(sk, skb);
         dccp_write_xmit(sk);
 out_release:
         release_sock(sk);