[RFC net-next PATCH V3 1/2] net: Functions to report space available in device TX queues

[Jesper Dangaard Brouer <brouer@redhat.com>]

From: Tom Herbert <therbert@google.com>

This patch adds netdev_tx_avail_queue and netdev_avail_queue which are
used to report number of bytes available in transmit queues per BQL. The
functions call dql_avail which returns BQL limit minus number of
inflight bytes. These functions can be called without txlock, for
instance to ascertain how much data should be dequeued from a qdisc in
a batch. When called without the tx_lock, the result is technically a
hint, subsequently when the tx_lock is done for a transmit it is
possible the availability has changed (for example a transmit
completion may have freed up more space in the queue or changed the
limit).

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>

---
 - Fixed spelling in comments

 include/linux/netdevice.h |   28 ++++++++++++++++++++++++++--
 1 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 28d4378..b12b919 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2551,6 +2551,30 @@ static inline void netdev_completed_queue(struct net_device *dev,
 	netdev_tx_completed_queue(netdev_get_tx_queue(dev, 0), pkts, bytes);
 }
 
+static inline int netdev_tx_avail_queue(struct netdev_queue *dev_queue)
+{
+#ifdef CONFIG_BQL
+	return dql_avail(&dev_queue->dql);
+#else
+	return DQL_MAX_LIMIT;
+#endif
+}
+
+/**
+ *	netdev_avail_queue - report how much space is available for xmit
+ *	@dev: network device
+ *
+ *	Report the amount of space available in the TX queue in terms of
+ *	number of bytes. This returns the number of bytes available per
+ *	DQL. This function may be called without taking the txlock on
+ *	the device, however in that case the result should be taken as
+ *	a (strong) hint.
+ */
+static inline int netdev_avail_queue(struct net_device *dev)
+{
+	return netdev_tx_avail_queue(netdev_get_tx_queue(dev, 0));
+}
+
 static inline void netdev_tx_reset_queue(struct netdev_queue *q)
 {
 #ifdef CONFIG_BQL
@@ -2566,9 +2590,9 @@ static inline void netdev_tx_reset_queue(struct netdev_queue *q)
  * 	Reset the bytes and packet count of a network device and clear the
  * 	software flow control OFF bit for this network device
  */
-static inline void netdev_reset_queue(struct net_device *dev_queue)
+static inline void netdev_reset_queue(struct net_device *dev)
 {
-	netdev_tx_reset_queue(netdev_get_tx_queue(dev_queue, 0));
+	netdev_tx_reset_queue(netdev_get_tx_queue(dev, 0));
 }
 
 /**