1 files changed, 32 insertions, 11 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;