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, 35 insertions, 0 deletions

diff --git a/include/linux/can/skb.h b/include/linux/can/skb.h
new file mode 100644
index 000000000000..4b0f24d3a878
--- /dev/null
+++ b/include/linux/can/skb.h
@@ -0,0 +1,35 @@
+/*
+ * linux/can/skb.h
+ *
+ * Definitions for the CAN network socket buffer
+ *
+ * Copyright (C) 2012 Oliver Hartkopp <socketcan@hartkopp.net>
+ *
+ */
+
+#ifndef CAN_SKB_H
+#define CAN_SKB_H
+
+#include <linux/types.h>
+#include <linux/can.h>
+
+/*
+ * 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.
+ * N.B. that this information must not be modified in cloned CAN sk_buffs.
+ * To modify the CAN frame content or the struct can_skb_priv content
+ * skb_copy() needs to be used instead of skb_clone().
+ */
+
+/**
+ * struct can_skb_priv - private additional data inside CAN sk_buffs
+ * @ifindex:    ifindex of the first interface the CAN frame appeared on
+ * @cf:         align to the following CAN frame at skb->data
+ */
+struct can_skb_priv {
+        int ifindex;
+        struct can_frame cf[0];
+};
+
+#endif /* CAN_SKB_H */