3 files changed, 66 insertions, 18 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 083b5989cecb..8b266390b9e2 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -63,27 +63,48 @@ struct wireless_dev;
 #define HAVE_FREE_NETDEV                /* free_netdev() */
 #define HAVE_NETDEV_PRIV                /* netdev_priv() */
 
-#define NET_XMIT_SUCCESS        0
-#define NET_XMIT_DROP           1       /* skb dropped                  */
-#define NET_XMIT_CN             2       /* congestion notification      */
-#define NET_XMIT_POLICED        3       /* skb is shot by police        */
-#define NET_XMIT_MASK           0xFFFF  /* qdisc flags in net/sch_generic.h */
+/*
+ * Transmit return codes: transmit return codes originate from three different
+ * namespaces:
+ *
+ * - qdisc return codes
+ * - driver transmit return codes
+ * - errno values
+ *
+ * Drivers are allowed to return any one of those in their hard_start_xmit()
+ * function. Real network devices commonly used with qdiscs should only return
+ * the driver transmit return codes though - when qdiscs are used, the actual
+ * transmission happens asynchronously, so the value is not propagated to
+ * higher layers. Virtual network devices transmit synchronously, in this case
+ * the driver transmit return codes are consumed by dev_queue_xmit(), all
+ * others are propagated to higher layers.
+ */
+
+/* qdisc ->enqueue() return codes. */
+#define NET_XMIT_SUCCESS        0x00
+#define NET_XMIT_DROP           0x10    /* skb dropped                  */
+#define NET_XMIT_CN             0x20    /* congestion notification      */
+#define NET_XMIT_POLICED        0x30    /* skb is shot by police        */
+#define NET_XMIT_MASK           0xf0    /* qdisc flags in net/sch_generic.h */
 
 /* Backlog congestion levels */
-#define NET_RX_SUCCESS          0   /* keep 'em coming, baby */
-#define NET_RX_DROP             1  /* packet dropped */
+#define NET_RX_SUCCESS          0       /* keep 'em coming, baby */
+#define NET_RX_DROP             1       /* packet dropped */
 
 /* NET_XMIT_CN is special. It does not guarantee that this packet is lost. It
  * indicates that the device will soon be dropping packets, or already drops
  * some packets of the same priority; prompting us to send less aggressively. */
-#define net_xmit_eval(e)        ((e) == NET_XMIT_CN? 0 : (e))
+#define net_xmit_eval(e)        ((e) == NET_XMIT_CN ? 0 : (e))
 #define net_xmit_errno(e)       ((e) != NET_XMIT_CN ? -ENOBUFS : 0)
 
 /* Driver transmit return codes */
+#define NETDEV_TX_MASK          0xf
+
 enum netdev_tx {
-        NETDEV_TX_OK = 0,       /* driver took care of packet */
-        NETDEV_TX_BUSY,         /* driver tx path was busy*/
-        NETDEV_TX_LOCKED = -1,  /* driver tx lock was already taken */
+        __NETDEV_TX_MIN  = INT_MIN,     /* make sure enum is signed */
+        NETDEV_TX_OK     = 0,           /* driver took care of packet */
+        NETDEV_TX_BUSY   = 1,           /* driver tx path was busy*/
+        NETDEV_TX_LOCKED = 2,           /* driver tx lock was already taken */
 };
 typedef enum netdev_tx netdev_tx_t;
 
diff --git a/net/core/dev.c b/net/core/dev.c
index ad8e320ceba7..548340b57296 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1757,7 +1757,7 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
                         struct netdev_queue *txq)
 {
         const struct net_device_ops *ops = dev->netdev_ops;
-        int rc;
+        int rc = NETDEV_TX_OK;
 
         if (likely(!skb->next)) {
                 if (!list_empty(&ptype_all))
@@ -1805,6 +1805,8 @@ gso:
                 nskb->next = NULL;
                 rc = ops->ndo_start_xmit(nskb, dev);
                 if (unlikely(rc != NETDEV_TX_OK)) {
+                        if (rc & ~NETDEV_TX_MASK)
+                                goto out_kfree_gso_skb;
                         nskb->next = skb->next;
                         skb->next = nskb;
                         return rc;
@@ -1814,11 +1816,12 @@ gso:
                         return NETDEV_TX_BUSY;
         } while (skb->next);
 
-        skb->destructor = DEV_GSO_CB(skb)->destructor;
-
+out_kfree_gso_skb:
+        if (likely(skb->next == NULL))
+                skb->destructor = DEV_GSO_CB(skb)->destructor;
 out_kfree_skb:
         kfree_skb(skb);
-        return NETDEV_TX_OK;
+        return rc;
 }
 
 static u32 skb_tx_hashrnd;
@@ -1906,6 +1909,23 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
         return rc;
 }
 
+static inline bool dev_xmit_complete(int rc)
+{
+        /* successful transmission */
+        if (rc == NETDEV_TX_OK)
+                return true;
+
+        /* error while transmitting, driver consumed skb */
+        if (rc < 0)
+                return true;
+
+        /* error while queueing to a different device, driver consumed skb */
+        if (rc & NET_XMIT_MASK)
+                return true;
+
+        return false;
+}
+
 /**
  *      dev_queue_xmit - transmit a buffer
  *      @skb: buffer to transmit
@@ -2003,8 +2023,8 @@ gso:
                         HARD_TX_LOCK(dev, txq, cpu);
 
                         if (!netif_tx_queue_stopped(txq)) {
-                                rc = NET_XMIT_SUCCESS;
-                                if (!dev_hard_start_xmit(skb, dev, txq)) {
+                                rc = dev_hard_start_xmit(skb, dev, txq);
+                                if (dev_xmit_complete(rc)) {
                                         HARD_TX_UNLOCK(dev, txq);
                                         goto out;
                                 }
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 4ae6aa562f2b..b13821ad2fb6 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -120,8 +120,15 @@ int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
 
         HARD_TX_LOCK(dev, txq, smp_processor_id());
         if (!netif_tx_queue_stopped(txq) &&
-            !netif_tx_queue_frozen(txq))
+            !netif_tx_queue_frozen(txq)) {
                 ret = dev_hard_start_xmit(skb, dev, txq);
+
+                /* an error implies that the skb was consumed */
+                if (ret < 0)
+                        ret = NETDEV_TX_OK;
+                /* all NET_XMIT codes map to NETDEV_TX_OK */
+                ret &= ~NET_XMIT_MASK;
+        }
         HARD_TX_UNLOCK(dev, txq);
 
         spin_lock(root_lock);