Linux Ethernet Bridging - May 2021 - [Bridge] [RFC net-next 2/9] net: bridge: Disambiguate offload_fwd_mark

Before this change, four related - but distinct - concepts where named
offload_fwd_mark:

- skb->offload_fwd_mark: Set by the switchdev driver if the underlying
  hardware has already forwarded this frame to the other ports in the
  same hardware domain.

- nbp->offload_fwd_mark: An idetifier used to group ports that share
  the same hardware forwarding domain.

- br->offload_fwd_mark: Counter used to make sure that unique IDs are
  used in cases where a bridge contains ports from multiple hardware
  domains.

- skb->cb->offload_fwd_mark: The hardware domain on which the frame
  ingressed and was forwarded.

Introduce the term "hardware forwarding domain" ("hwdom") in
the
bridge to denote a set of ports with the following property:

    If an skb with skb->offload_fwd_mark set, is received on a port
    belonging to hwdom N, that frame has already been forwarded to all
    other ports in hwdom N.

By decoupling the name from "offload_fwd_mark", we can extend the
term's definition in the future - e.g. to add constraints that
describe expected egress behavior - without overloading the meaning of
"offload_fwd_mark".

- nbp->offload_fwd_mark thus becomes nbp->hwdom.

- br->offload_fwd_mark becomes br->last_hwdom.

- skb->cb->offload_fwd_mark becomes skb->cb->src_hwdom. There is a
  slight change here: Whereas previously this was only set for
  offloaded packets, we now always track the incoming hwdom. As all
  uses where already gated behind checks of skb->offload_fwd_mark,
  this will not introduce any functional change, but it paves the way
  for future changes where the ingressing hwdom must be known both for
  offloaded and non-offloaded frames.

Signed-off-by: Tobias Waldekranz <tobias at waldekranz.com>
---
 net/bridge/br_if.c        |  2 +-
 net/bridge/br_private.h   | 10 +++++-----
 net/bridge/br_switchdev.c | 16 ++++++++--------
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
index f7d2f472ae24..73fa703f8df5 100644
--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -643,7 +643,7 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
 	if (err)
 		goto err5;
 
-	err = nbp_switchdev_mark_set(p);
+	err = nbp_switchdev_hwdom_set(p);
 	if (err)
 		goto err6;
 
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 7ce8a77cc6b6..53248715f631 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -327,7 +327,7 @@ struct net_bridge_port {
 	struct netpoll			*np;
 #endif
 #ifdef CONFIG_NET_SWITCHDEV
-	int				offload_fwd_mark;
+	int				hwdom;
 #endif
 	u16				group_fwd_mask;
 	u16				backup_redirected_cnt;
@@ -472,7 +472,7 @@ struct net_bridge {
 	u32				auto_cnt;
 
 #ifdef CONFIG_NET_SWITCHDEV
-	int offload_fwd_mark;
+	int last_hwdom;
 #endif
 	struct hlist_head		fdb_list;
 
@@ -502,7 +502,7 @@ struct br_input_skb_cb {
 #endif
 
 #ifdef CONFIG_NET_SWITCHDEV
-	int offload_fwd_mark;
+	int src_hwdom;
 #endif
 };
 
@@ -1593,7 +1593,7 @@ static inline void br_sysfs_delbr(struct net_device *dev)
{ return; }
 
 /* br_switchdev.c */
 #ifdef CONFIG_NET_SWITCHDEV
-int nbp_switchdev_mark_set(struct net_bridge_port *p);
+int nbp_switchdev_hwdom_set(struct net_bridge_port *p);
 void nbp_switchdev_frame_mark(const struct net_bridge_port *p,
 			      struct sk_buff *skb);
 bool nbp_switchdev_allowed_egress(const struct net_bridge_port *p,
@@ -1613,7 +1613,7 @@ static inline void br_switchdev_frame_unmark(struct
sk_buff *skb)
 	skb->offload_fwd_mark = 0;
 }
 #else
-static inline int nbp_switchdev_mark_set(struct net_bridge_port *p)
+static inline int nbp_switchdev_hwdom_set(struct net_bridge_port *p)
 {
 	return 0;
 }
diff --git a/net/bridge/br_switchdev.c b/net/bridge/br_switchdev.c
index a5e601e41cb9..bc085077ae71 100644
--- a/net/bridge/br_switchdev.c
+++ b/net/bridge/br_switchdev.c
@@ -8,20 +8,20 @@
 
 #include "br_private.h"
 
-static int br_switchdev_mark_get(struct net_bridge *br, struct net_device *dev)
+static int br_switchdev_hwdom_get(struct net_bridge *br, struct net_device
*dev)
 {
 	struct net_bridge_port *p;
 
 	/* dev is yet to be added to the port list. */
 	list_for_each_entry(p, &br->port_list, list) {
 		if (netdev_port_same_parent_id(dev, p->dev))
-			return p->offload_fwd_mark;
+			return p->hwdom;
 	}
 
-	return ++br->offload_fwd_mark;
+	return ++br->last_hwdom;
 }
 
-int nbp_switchdev_mark_set(struct net_bridge_port *p)
+int nbp_switchdev_hwdom_set(struct net_bridge_port *p)
 {
 	struct netdev_phys_item_id ppid = { };
 	int err;
@@ -35,7 +35,7 @@ int nbp_switchdev_mark_set(struct net_bridge_port *p)
 		return err;
 	}
 
-	p->offload_fwd_mark = br_switchdev_mark_get(p->br, p->dev);
+	p->hwdom = br_switchdev_hwdom_get(p->br, p->dev);
 
 	return 0;
 }
@@ -43,15 +43,15 @@ int nbp_switchdev_mark_set(struct net_bridge_port *p)
 void nbp_switchdev_frame_mark(const struct net_bridge_port *p,
 			      struct sk_buff *skb)
 {
-	if (skb->offload_fwd_mark &&
!WARN_ON_ONCE(!p->offload_fwd_mark))
-		BR_INPUT_SKB_CB(skb)->offload_fwd_mark = p->offload_fwd_mark;
+	if (p->hwdom)
+		BR_INPUT_SKB_CB(skb)->src_hwdom = p->hwdom;
 }
 
 bool nbp_switchdev_allowed_egress(const struct net_bridge_port *p,
 				  const struct sk_buff *skb)
 {
 	return !skb->offload_fwd_mark ||
-	       BR_INPUT_SKB_CB(skb)->offload_fwd_mark != p->offload_fwd_mark;
+	       BR_INPUT_SKB_CB(skb)->src_hwdom != p->hwdom;
 }
 
 /* Flags that can be offloaded to hardware */
-- 
2.25.1

On Mon, Apr 26, 2021 at 07:04:04PM +0200, Tobias Waldekranz
wrote:
> - skb->cb->offload_fwd_mark becomes skb->cb->src_hwdom. There
is a
>   slight change here: Whereas previously this was only set for
>   offloaded packets, we now always track the incoming hwdom. As all
>   uses where already gated behind checks of skb->offload_fwd_mark,
>   this will not introduce any functional change, but it paves the way
>   for future changes where the ingressing hwdom must be known both for
>   offloaded and non-offloaded frames.
[...]
> @@ -43,15 +43,15 @@ int nbp_switchdev_mark_set(struct net_bridge_port *p)
>  void nbp_switchdev_frame_mark(const struct net_bridge_port *p,
>  			      struct sk_buff *skb)
>  {
> -	if (skb->offload_fwd_mark &&
!WARN_ON_ONCE(!p->offload_fwd_mark))
> -		BR_INPUT_SKB_CB(skb)->offload_fwd_mark = p->offload_fwd_mark;
> +	if (p->hwdom)
> +		BR_INPUT_SKB_CB(skb)->src_hwdom = p->hwdom;
>  }
I assume you are referring to this change? "src_hwdom" sounds weird if
it's expected to be valid for non-offloaded frames.

Can you elaborate about "future changes where the ingressing hwdom must
be known both for offloaded and non-offloaded frames"?

Probably best to split this change to a different patch given the rest
of the changes are mechanical.
>  
>  bool nbp_switchdev_allowed_egress(const struct net_bridge_port *p,
>  				  const struct sk_buff *skb)
>  {
>  	return !skb->offload_fwd_mark ||
> -	       BR_INPUT_SKB_CB(skb)->offload_fwd_mark !=
p->offload_fwd_mark;
> +	       BR_INPUT_SKB_CB(skb)->src_hwdom != p->hwdom;
>  }
>  
>  /* Flags that can be offloaded to hardware */
> -- 
> 2.25.1
>