On Fri, Oct 15, 2010 at 10:37 AM, Kurt Van Dijck <[email protected]> wrote:
> CAN has no addressing scheme. It is currently impossible
> for userspace to tell is a received CAN frame comes from
> another process on the local host, or from a remote CAN
> device.
> This patch add support for userspace applications to distinguish
> between 'own', 'local' and 'remote' CAN traffic.
> Distinction is made by returning some flags in msg->msg_flags
> in the call to recvmsg.
> MSG_CONFIRM flag means 'own', as in 'transmission confirmation'
> MSG_DONTROUTE flag means 'local', not routed.
> Obviously, msgs with MSG_CONFIRM will have MSG_DONTROUTE set too.
>
> Please note that on SocketCAN mailing list, different opinions
> exist on the exact meaning of MSG_DONTROUTE. Better (=more
> intuitive) alternatives are appreciated.
>
> Signed-off-by: Kurt Van Dijck <[email protected]>
> ---
> net/can/raw.c | 33 ++++++++++++++++++++++++++++++---
> 1 files changed, 30 insertions(+), 3 deletions(-)
>
> diff --git a/net/can/raw.c b/net/can/raw.c
> index 7d77e67..f98709e 100644
> --- a/net/can/raw.c
> +++ b/net/can/raw.c
> @@ -90,23 +90,39 @@ struct raw_sock {
> can_err_mask_t err_mask;
> };
>
> +/*
> + * return some space to store extra msg flags in.
> + * We use 1 int beyond the 'struct sockaddr_can' in skb->cb
> + * to store those.
> + * These flags will be use in raw_recvmsg()
> + */
> +static inline int *raw_flags(struct sk_buff *skb)
> +{
> + BUILD_BUG_ON(sizeof(skb->cb)
> + <= (sizeof(struct sockaddr_can) + sizeof(int)));
> + /* return pointer after struct sockaddr_can */
> + return (int *)(&((struct sockaddr_can *)skb->cb)[1]);
Since msg_flags is unsigned, it would be nice if this function returns unsigned.
> +}
> +
> static inline struct raw_sock *raw_sk(const struct sock *sk)
> {
> return (struct raw_sock *)sk;
> }
>
> -static void raw_rcv(struct sk_buff *skb, void *data)
> +static void raw_rcv(struct sk_buff *oskb, void *data)
> {
> struct sock *sk = (struct sock *)data;
> struct raw_sock *ro = raw_sk(sk);
> struct sockaddr_can *addr;
> + struct sk_buff *skb;
> + int *pflags;
>
> /* check the received tx sock reference */
> - if (!ro->recv_own_msgs && skb->sk == sk)
> + if (!ro->recv_own_msgs && oskb->sk == sk)
> return;
>
> /* clone the given skb to be able to enqueue it into the rcv queue */
> - skb = skb_clone(skb, GFP_ATOMIC);
> + skb = skb_clone(oskb, GFP_ATOMIC);
> if (!skb)
> return;
>
> @@ -123,6 +139,14 @@ static void raw_rcv(struct sk_buff *skb, void *data)
> addr->can_family = AF_CAN;
> addr->can_ifindex = skb->dev->ifindex;
>
> + /* prepare the flags for raw_recvmsg() */
> + pflags = raw_flags(skb);
> + *pflags = 0;
> + if (oskb->sk)
> + *pflags |= MSG_DONTROUTE;
> + if (oskb->sk == sk)
> + *pflags |= MSG_CONFIRM;
> +
> if (sock_queue_rcv_skb(sk, skb) < 0)
> kfree_skb(skb);
> }
> @@ -707,6 +731,9 @@ static int raw_recvmsg(struct kiocb *iocb, struct socket
> *sock,
> memcpy(msg->msg_name, skb->cb, msg->msg_namelen);
> }
>
> + /* assign the flags that have been recorded in in raw_rcv() */
small typo: double in
> + msg->msg_flags |= *(raw_flags(skb));
> +
> skb_free_datagram(sk, skb);
>
> return size;
thanks,
Daniel.
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