[Patch net-next v2 2/3] net_sched: plug in qdisc ops change_tx_queue_len

[Cong Wang <xiyou.wangcong@gmail.com>]

Introduce a new qdisc ops ->change_tx_queue_len() so that
each qdisc could decide how to implement this if it wants.
Previously we simply read dev->tx_queue_len, after pfifo_fast
switches to skb array, we need this API to resize the skb array
when we change dev->tx_queue_len.

To avoid handling race conditions with TX BH, we need to
deactivate all TX queues before change the value and bring them
back after we are done, this also makes implementation easier.

Cc: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 include/net/sch_generic.h |  2 ++
 net/core/dev.c            |  1 +
 net/sched/sch_generic.c   | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index cd1be1f25c36..d13dd129d085 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -200,6 +200,7 @@ struct Qdisc_ops {
 					  struct nlattr *arg,
 					  struct netlink_ext_ack *extack);
 	void			(*attach)(struct Qdisc *sch);
+	int			(*change_tx_queue_len)(struct Qdisc *, unsigned int);
 
 	int			(*dump)(struct Qdisc *, struct sk_buff *);
 	int			(*dump_stats)(struct Qdisc *, struct gnet_dump *);
@@ -488,6 +489,7 @@ void qdisc_class_hash_remove(struct Qdisc_class_hash *,
 void qdisc_class_hash_grow(struct Qdisc *, struct Qdisc_class_hash *);
 void qdisc_class_hash_destroy(struct Qdisc_class_hash *);
 
+int dev_qdisc_change_tx_queue_len(struct net_device *dev);
 void dev_init_scheduler(struct net_device *dev);
 void dev_shutdown(struct net_device *dev);
 void dev_activate(struct net_device *dev);
diff --git a/net/core/dev.c b/net/core/dev.c
index 913655e82859..a9d7d883416d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7059,6 +7059,7 @@ int dev_change_tx_queue_len(struct net_device *dev, unsigned long new_len)
 			dev->tx_queue_len = orig_len;
 			return res;
 		}
+		return dev_qdisc_change_tx_queue_len(dev);
 	}
 
 	return 0;
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 1816bde47256..08f9fa27e06e 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -1178,6 +1178,39 @@ void dev_deactivate(struct net_device *dev)
 }
 EXPORT_SYMBOL(dev_deactivate);
 
+static int qdisc_change_tx_queue_len(struct net_device *dev,
+				     struct netdev_queue *dev_queue)
+{
+	struct Qdisc *qdisc = dev_queue->qdisc_sleeping;
+	const struct Qdisc_ops *ops = qdisc->ops;
+
+	if (ops->change_tx_queue_len)
+		return ops->change_tx_queue_len(qdisc, dev->tx_queue_len);
+	return 0;
+}
+
+int dev_qdisc_change_tx_queue_len(struct net_device *dev)
+{
+	bool up = dev->flags & IFF_UP;
+	unsigned int i;
+	int ret = 0;
+
+	if (up)
+		dev_deactivate(dev);
+
+	for (i = 0; i < dev->num_tx_queues; i++) {
+		ret = qdisc_change_tx_queue_len(dev, &dev->_tx[i]);
+
+		/* TODO: revert changes on a partial failure */
+		if (ret)
+			break;
+	}
+
+	if (up)
+		dev_activate(dev);
+	return ret;
+}
+
 static void dev_init_scheduler_queue(struct net_device *dev,
 				     struct netdev_queue *dev_queue,
 				     void *_qdisc)
-- 
2.13.0