Commit 1e55659c authored by Oliver Hartkopp's avatar Oliver Hartkopp Committed by David S. Miller
Browse files

can-raw: add msg_flags to distinguish local traffic 



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. The distinction is made by returning
flags in msg->msg_flags in the call to recvmsg().

The added documentation explains the introduced flags.

Signed-off-by: default avatarKurt Van Dijck <kurt.van.dijck@eia.be>
Signed-off-by: default avatarOliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 32a875ad

Documentation/networking/can.txt

+12 −0
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ This file contains 
      4.1.2 RAW socket option CAN_RAW_ERR_FILTER

      4.1.3 RAW socket option CAN_RAW_LOOPBACK

      4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS

      4.1.5 RAW socket returned message flags

    4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)

    4.3 connected transport protocols (SOCK_SEQPACKET)

    4.4 unconnected transport protocols (SOCK_DGRAM)
@@ -471,6 +472,17 @@ solution for a couple of reasons: 
    setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,

               &recv_own_msgs, sizeof(recv_own_msgs));



  4.1.5 RAW socket returned message flags



  When using recvmsg() call, the msg->msg_flags may contain following flags:



    MSG_DONTROUTE: set when the received frame was created on the local host.



    MSG_CONFIRM: set when the frame was sent via the socket it is received on.

      This flag can be interpreted as a 'transmission confirmation' when the

      CAN driver supports the echo of frames on driver level, see 3.2 and 6.2.

      In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.



  4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)

  4.3 connected transport protocols (SOCK_SEQPACKET)

  4.4 unconnected transport protocols (SOCK_DGRAM)

net/can/raw.c

+30 −3
Original line number Diff line number Diff line
@@ -90,23 +90,39 @@ struct raw_sock { 
	can_err_mask_t err_mask;

};



/*

 * Return pointer to store the extra msg flags for raw_recvmsg().

 * We use the space of one unsigned int beyond the 'struct sockaddr_can'

 * in skb->cb.

 */

static inline unsigned int *raw_flags(struct sk_buff *skb)

{

	BUILD_BUG_ON(sizeof(skb->cb) <= (sizeof(struct sockaddr_can) +

					 sizeof(unsigned int)));



	/* return pointer after struct sockaddr_can */

	return (unsigned int *)(&((struct sockaddr_can *)skb->cb)[1]);

}



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;

	unsigned 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;



	/* add CAN specific message 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 raw_rcv() */

	msg->msg_flags |= *(raw_flags(skb));



	skb_free_datagram(sk, skb);



	return size;

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