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, 6 insertions, 2 deletions

diff --git a/net/can/raw.c b/net/can/raw.c
index 5b0e3e330d97..5d860e8dcc52 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -50,6 +50,7 @@
 #include <linux/skbuff.h>
 #include <linux/can.h>
 #include <linux/can/core.h>
+#include <linux/can/skb.h>
 #include <linux/can/raw.h>
 #include <net/sock.h>
 #include <net/net_namespace.h>
@@ -699,11 +700,14 @@ static int raw_sendmsg(struct kiocb *iocb, struct socket *sock,
         if (!dev)
                 return -ENXIO;
 
-        skb = sock_alloc_send_skb(sk, size, msg->msg_flags & MSG_DONTWAIT,
-                                  &err);
+        skb = sock_alloc_send_skb(sk, size + sizeof(struct can_skb_priv),
+                                  msg->msg_flags & MSG_DONTWAIT, &err);
         if (!skb)
                 goto put_dev;
 
+        skb_reserve(skb, sizeof(struct can_skb_priv));
+        ((struct can_skb_priv *)(skb->head))->ifindex = dev->ifindex;
+
         err = memcpy_fromiovec(skb_put(skb, size), msg->msg_iov, size);
         if (err < 0)
                 goto free_skb;