netdevice: document NETDEV_TX_BUSY deprecation.
This paraphrases DaveM (and steals some of his words) explaining why
a device shouldn't return NETDEV_TX_BUSY, even though it looks so inviting
to driver authors.
See http://www.spinics.net/lists/netdev/msg322350.html
Inspired-by: David Miller <davem@davemloft.net>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 846a1f5..a710d22 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -795,7 +795,10 @@
* netdev_tx_t (*ndo_start_xmit)(struct sk_buff *skb,
* struct net_device *dev);
* Called when a packet needs to be transmitted.
- * Must return NETDEV_TX_OK , NETDEV_TX_BUSY.
+ * Returns NETDEV_TX_OK. Can return NETDEV_TX_BUSY, but you should stop
+ * the queue before that can happen; it's for obsolete devices and weird
+ * corner cases, but the stack really does a non-trivial amount
+ * of useless work if you return NETDEV_TX_BUSY.
* (can also return NETDEV_TX_LOCKED iff NETIF_F_LLTX)
* Required can not be NULL.
*