[PATCH net-next v2] net: dqs: introduce IFF_NO_BQL private flag for non-BQL drivers

[Jason Xing <kerneljasonxing@gmail.com>]

From: Jason Xing <kernelxing@tencent.com>

Since commit 74293ea1c4db6 ("net: sysfs: Do not create sysfs for non
BQL device") limits the non-BQL driver not creating byte_queue_limits
directory, I found there is one exception, namely, virtio-net driver,
which should also be limited in netdev_uses_bql(). Let me give it a
try first.

I decided to introduce a NO_BQL bit because:
1) it can help us limit virtio-net driver for now.
2) if we found another non-BQL driver, we can take it into account.
3) we can replace all the driver meeting those two statements in
netdev_uses_bql() in future.

For now, I would like to make the first step to use this new bit for dqs
use instead of replacing/applying all the non-BQL drivers in one go.

As Jakub said, "netdev_uses_bql() is best effort", I think, we can add
new non-BQL drivers as soon as we find one.

After this patch, there is no byte_queue_limits directory in virtio-net
driver.

Signed-off-by: Jason Xing <kernelxing@tencent.com>
---
v2
Link: https://lore.kernel.org/all/20240609131732.73156-1-kerneljasonxing@gmail.com/
1. chose to add the new bit into enum netdev_priv_flags() instead of
breaking the room of device feature.
---
 drivers/net/virtio_net.c  | 2 +-
 include/linux/netdevice.h | 4 ++++
 net/core/net-sysfs.c      | 2 +-
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 61a57d134544..728f4b9844cc 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -5631,7 +5631,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 	/* Set up network device as normal. */
 	dev->priv_flags |= IFF_UNICAST_FLT | IFF_LIVE_ADDR_CHANGE |
-			   IFF_TX_SKB_NO_LINEAR;
+			   IFF_TX_SKB_NO_LINEAR | IFF_NO_BQL;
 	dev->netdev_ops = &virtnet_netdev;
 	dev->stat_ops = &virtnet_stat_ops;
 	dev->features = NETIF_F_HIGHDMA;
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d20c6c99eb88..6d379858d11f 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1649,6 +1649,9 @@ struct net_device_ops {
  * @IFF_SEE_ALL_HWTSTAMP_REQUESTS: device wants to see calls to
  *	ndo_hwtstamp_set() for all timestamp requests regardless of source,
  *	even if those aren't HWTSTAMP_SOURCE_NETDEV.
+ * @IFF_NO_BQL: driver doesn't use BQL for flow control for now. It's used
+ *	to check if we should create byte_queue_limits directory in dqs
+ *	(see netdev_uses_bql())
  */
 enum netdev_priv_flags {
 	IFF_802_1Q_VLAN			= 1<<0,
@@ -1685,6 +1688,7 @@ enum netdev_priv_flags {
 	IFF_TX_SKB_NO_LINEAR		= BIT_ULL(31),
 	IFF_CHANGE_PROTO_DOWN		= BIT_ULL(32),
 	IFF_SEE_ALL_HWTSTAMP_REQUESTS	= BIT_ULL(33),
+	IFF_NO_BQL			= BIT_ULL(34),
 };
 
 #define IFF_802_1Q_VLAN			IFF_802_1Q_VLAN
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 4c27a360c294..7d99fbbad6af 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1765,7 +1765,7 @@ static const struct kobj_type netdev_queue_ktype = {
 static bool netdev_uses_bql(const struct net_device *dev)
 {
 	if (dev->features & NETIF_F_LLTX ||
-	    dev->priv_flags & IFF_NO_QUEUE)
+	    dev->priv_flags & (IFF_NO_QUEUE | IFF_NO_BQL))
 		return false;
 
 	return IS_ENABLED(CONFIG_BQL);
-- 
2.37.3