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 <>
Signed-off-by: default avatarOliver Hartkopp <>
Signed-off-by: default avatarDavid S. Miller <>
parent 32a875ad
......@@ -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:
&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)
......@@ -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)
/* 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)
......@@ -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)
......@@ -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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