can: dev: extend struct can_skb_priv to hold CAN frame length

In order to implement byte queue limits (bql) in CAN drivers, the length of the
CAN frame needs to be passed into the networking stack after queueing and after
transmission completion.

To avoid to calculate this length twice, extend the struct can_skb_priv to hold
the length of the CAN frame and extend __can_get_echo_skb() to return that
value.
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/r/20210111141930.693847-12-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/dev/rx-offload.c

@@ -271,7 +271,7 @@ unsigned int can_rx_offload_get_echo_skb(struct can_rx_offload *offload,
 	u8 len;
 	int err;
 
-	skb = __can_get_echo_skb(dev, idx, &len);
+	skb = __can_get_echo_skb(dev, idx, &len, NULL);
 	if (!skb)
 		return 0;
 

drivers/net/can/dev/skb.c

@@ -76,7 +76,8 @@ int can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,
 EXPORT_SYMBOL_GPL(can_put_echo_skb);
 
 struct sk_buff *
-__can_get_echo_skb(struct net_device *dev, unsigned int idx, u8 *len_ptr)
+__can_get_echo_skb(struct net_device *dev, unsigned int idx, u8 *len_ptr,
+		   unsigned int *frame_len_ptr)
 {
 	struct can_priv *priv = netdev_priv(dev);
 
@@ -91,6 +92,7 @@ __can_get_echo_skb(struct net_device *dev, unsigned int idx, u8 *len_ptr)
 		 * length is supported on both CAN and CANFD frames.
 		 */
 		struct sk_buff *skb = priv->echo_skb[idx];
+		struct can_skb_priv *can_skb_priv = can_skb_prv(skb);
 		struct canfd_frame *cf = (struct canfd_frame *)skb->data;
 
 		/* get the real payload length for netdev statistics */
@@ -99,6 +101,9 @@ __can_get_echo_skb(struct net_device *dev, unsigned int idx, u8 *len_ptr)
 		else
 			*len_ptr = cf->len;
 
+		if (frame_len_ptr)
+			*frame_len_ptr = can_skb_priv->frame_len;
+
 		priv->echo_skb[idx] = NULL;
 
 		return skb;
@@ -118,7 +123,7 @@ unsigned int can_get_echo_skb(struct net_device *dev, unsigned int idx)
 	struct sk_buff *skb;
 	u8 len;
 
-	skb = __can_get_echo_skb(dev, idx, &len);
+	skb = __can_get_echo_skb(dev, idx, &len, NULL);
 	if (!skb)
 		return 0;
 

include/linux/can/skb.h

@@ -20,7 +20,7 @@ void can_flush_echo_skb(struct net_device *dev);
 int can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,
 		     unsigned int idx);
 struct sk_buff *__can_get_echo_skb(struct net_device *dev, unsigned int idx,
-				   u8 *len_ptr);
+				   u8 *len_ptr, unsigned int *frame_len_ptr);
 unsigned int can_get_echo_skb(struct net_device *dev, unsigned int idx);
 void can_free_echo_skb(struct net_device *dev, unsigned int idx);
 struct sk_buff *alloc_can_skb(struct net_device *dev, struct can_frame **cf);
@@ -42,11 +42,13 @@ struct sk_buff *alloc_can_err_skb(struct net_device *dev,
  * struct can_skb_priv - private additional data inside CAN sk_buffs
  * @ifindex:	ifindex of the first interface the CAN frame appeared on
  * @skbcnt:	atomic counter to have an unique id together with skb pointer
+ * @frame_len:	length of CAN frame in data link layer
  * @cf:		align to the following CAN frame at skb->data
  */
 struct can_skb_priv {
 	int ifindex;
 	int skbcnt;
+	unsigned int frame_len;
 	struct can_frame cf[];
 };