On Tue, May 04, 2021 at 04:44:31PM +0200, Tobias Waldekranz wrote:

On Tue, Apr 27, 2021 at 13:17, Vladimir Oltean [off-list ref] wrote:

quoted

On Mon, Apr 26, 2021 at 07:04:08PM +0200, Tobias Waldekranz wrote:

quoted

Allow DSA drivers to support forward offloading from a bridge by:

- Passing calls to .ndo_dfwd_{add,del}_station to the drivers.

- Recording the subordinate device of offloaded skbs in the control
  buffer so that the tagger can take the appropriate action.

Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
---
 include/net/dsa.h |  7 +++++++
 net/dsa/slave.c   | 36 ++++++++++++++++++++++++++++++++++--
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 1f9ba9889034..77d4df819299 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h

@@ -119,6 +119,7 @@ struct dsa_netdevice_ops {
 
 struct dsa_skb_cb {
 	struct sk_buff *clone;
+	struct net_device *sb_dev;
 };
 
 struct __dsa_skb_cb {

@@ -828,6 +829,12 @@ struct dsa_switch_ops {
 					  const struct switchdev_obj_ring_role_mrp *mrp);
 	int	(*port_mrp_del_ring_role)(struct dsa_switch *ds, int port,
 					  const struct switchdev_obj_ring_role_mrp *mrp);
+
+	/* L2 forward offloading */
+	void *	(*dfwd_add_station)(struct dsa_switch *ds, int port,
+				    struct net_device *sb_dev);
+	void	(*dfwd_del_station)(struct dsa_switch *ds, int port,
+				    struct net_device *sb_dev);
 };
 
 #define DSA_DEVLINK_PARAM_DRIVER(_id, _name, _type, _cmodes)		\

diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 77b33bd161b8..3689ffa2dbb8 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c

@@ -657,6 +657,13 @@ static netdev_tx_t dsa_slave_xmit(struct sk_buff *skb, struct net_device *dev)
 	return dsa_enqueue_skb(nskb, dev);
 }
 
+static u16 dsa_slave_select_queue(struct net_device *dev, struct sk_buff *skb,
+				  struct net_device *sb_dev)
+{
+	DSA_SKB_CB(skb)->sb_dev = sb_dev;
+	return netdev_pick_tx(dev, skb, sb_dev);
+}
+

DSA_SKB_CB is going away:
https://patchwork.kernel.org/project/netdevbpf/patch/20210427042203.26258-5-yangbo.lu@nxp.com/

Let's either negotiate with Yangbo on keeping it, or make
.ndo_select_queue a bypass towards the tagger, where it can use its own
SKB_CB structure and be more flexible in general (I think I'm leaning
towards the latter).

Thus far, Yangbo is a tough negotiator, giving me the silent treatment:

https://lore.kernel.org/netdev/87y2d2noe5.fsf@waldekranz.com/ (local)

:)

That memset is giving me a hard time. I have just disabled it on my
branch at the moment. Any ideas on how to get rid of it without breaking
timestamping?

:)

Is there any guarantee written somewhere that the ownership of skb->cb
belongs to the NIC driver at the time of the ndo_select_queue call?

If there is, then the trivial solution is to just move the memset in
ndo_select_queue.

If there isn't, then we've got bigger issues (such as, for example, the
qdisc layer being able to overwrite your DSA_SKB_CB(skb)->sb_dev).