can: add private data space for CAN sk_buffs

The struct can_skb_priv is used to transport additional information along
with the stored struct can(fd)_frame that can not be contained in existing
struct sk_buff elements.

can_skb_priv is located in the skb headroom, which does not touch the existing
CAN sk_buff usage with skb->data and skb->len, so that even out-of-tree
CAN drivers can be used without changes.

Btw. out-of-tree CAN drivers without can_skb_priv in the sk_buff headroom
would not support features based on can_skb_priv.

The can_skb_priv->ifindex contains the first interface where the CAN frame
appeared on the local host. Unfortunately skb->skb_iif can not be used as this
value is overwritten in every netif_receive_skb() call.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
index 6abc6e59778e..59ada082a994 100644
--- a/drivers/net/can/dev.c
+++ b/drivers/net/can/dev.c
@@ -24,6 +24,7 @@
 #include <linux/if_arp.h>
 #include <linux/can.h>
 #include <linux/can/dev.h>
+#include <linux/can/skb.h>
 #include <linux/can/netlink.h>
 #include <linux/can/led.h>
 #include <net/rtnetlink.h>
@@ -502,13 +503,18 @@ struct sk_buff *alloc_can_skb(struct net_device *dev, struct can_frame **cf)
 {
         struct sk_buff *skb;
 
-        skb = netdev_alloc_skb(dev, sizeof(struct can_frame));
+        skb = netdev_alloc_skb(dev, sizeof(struct can_skb_priv) +
+                               sizeof(struct can_frame));
         if (unlikely(!skb))
                 return NULL;
 
         skb->protocol = htons(ETH_P_CAN);
         skb->pkt_type = PACKET_BROADCAST;
         skb->ip_summed = CHECKSUM_UNNECESSARY;
+
+        skb_reserve(skb, sizeof(struct can_skb_priv));
+        ((struct can_skb_priv *)(skb->head))->ifindex = dev->ifindex;
+
         *cf = (struct can_frame *)skb_put(skb, sizeof(struct can_frame));
         memset(*cf, 0, sizeof(struct can_frame));