can: bcm: add recvmsg flags for own, local and remote traffic

CAN RAW sockets allow userspace to tell if a received CAN frame comes
from the same socket, another socket on the same host, or another host.
See commit 1e55659ce6 ("can-raw: add msg_flags to distinguish local
traffic"). However, this feature is missing in CAN BCM sockets.

Add the same feature to CAN BCM sockets. When reading a received frame
(opcode RX_CHANGED) using recvmsg, two flags in msg->msg_flags may be
set following the previous convention (from CAN RAW), to distinguish
between 'own', 'local' and 'remote' CAN traffic.

Update the documentation to reflect this change.

Signed-off-by: Nicolas Maier <nicolas.maier.dev@gmail.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20240120081018.2319-1-socketcan@hartkopp.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Documentation/networking/can.rst

@@ -444,6 +444,24 @@ definitions are specified for CAN specific MTUs in include/linux/can.h:
   #define CANFD_MTU (sizeof(struct canfd_frame)) == 72  => CAN FD frame
 
 
+Returned Message Flags
+----------------------
+
+When using the system call recvmsg(2) on a RAW or a BCM socket, the
+msg->msg_flags field may contain the 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
+	:ref:`socketcan-local-loopback1` and :ref:`socketcan-local-loopback2`.
+	(Note: In order to receive such messages on a RAW socket,
+	CAN_RAW_RECV_OWN_MSGS must be set.)
+
+
 .. _socketcan-raw-sockets:
 
 RAW Protocol Sockets with can_filters (SOCK_RAW)
@@ -693,22 +711,6 @@ where the CAN_INV_FILTER flag is set in order to notch single CAN IDs or
 CAN ID ranges from the incoming traffic.
 
 
-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
-	:ref:`socketcan-local-loopback1` and :ref:`socketcan-local-loopback2`.
-	In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
-
-
 Broadcast Manager Protocol Sockets (SOCK_DGRAM)
 -----------------------------------------------
 

net/can/bcm.c

@@ -72,9 +72,11 @@
 #define BCM_TIMER_SEC_MAX (400 * 24 * 60 * 60)
 
 /* use of last_frames[index].flags */
+#define RX_LOCAL   0x10 /* frame was created on the local host */
+#define RX_OWN     0x20 /* frame was sent via the socket it was received on */
 #define RX_RECV    0x40 /* received data for this element */
 #define RX_THR     0x80 /* element not been sent due to throttle feature */
-#define BCM_CAN_FLAGS_MASK 0x3F /* to clean private flags after usage */
+#define BCM_CAN_FLAGS_MASK 0x0F /* to clean private flags after usage */
 
 /* get best masking value for can_rx_register() for a given single can_id */
 #define REGMASK(id) ((id & CAN_EFF_FLAG) ? \
@@ -138,6 +140,16 @@ static LIST_HEAD(bcm_notifier_list);
 static DEFINE_SPINLOCK(bcm_notifier_lock);
 static struct bcm_sock *bcm_busy_notifier;
 
+/* Return pointer to store the extra msg flags for bcm_recvmsg().
+ * We use the space of one unsigned int beyond the 'struct sockaddr_can'
+ * in skb->cb.
+ */
+static inline unsigned int *bcm_flags(struct sk_buff *skb)
+{
+	/* return pointer after struct sockaddr_can */
+	return (unsigned int *)(&((struct sockaddr_can *)skb->cb)[1]);
+}
+
 static inline struct bcm_sock *bcm_sk(const struct sock *sk)
 {
 	return (struct bcm_sock *)sk;
@@ -325,6 +337,7 @@ static void bcm_send_to_user(struct bcm_op *op, struct bcm_msg_head *head,
 	struct sock *sk = op->sk;
 	unsigned int datalen = head->nframes * op->cfsiz;
 	int err;
+	unsigned int *pflags;
 
 	skb = alloc_skb(sizeof(*head) + datalen, gfp_any());
 	if (!skb)
@@ -332,6 +345,14 @@ static void bcm_send_to_user(struct bcm_op *op, struct bcm_msg_head *head,
 
 	skb_put_data(skb, head, sizeof(*head));
 
+	/* ensure space for sockaddr_can and msg flags */
+	sock_skb_cb_check_size(sizeof(struct sockaddr_can) +
+			       sizeof(unsigned int));
+
+	/* initialize msg flags */
+	pflags = bcm_flags(skb);
+	*pflags = 0;
+
 	if (head->nframes) {
 		/* CAN frames starting here */
 		firstframe = (struct canfd_frame *)skb_tail_pointer(skb);
@@ -344,8 +365,14 @@ static void bcm_send_to_user(struct bcm_op *op, struct bcm_msg_head *head,
 		 * relevant for updates that are generated by the
 		 * BCM, where nframes is 1
 		 */
-		if (head->nframes == 1)
+		if (head->nframes == 1) {
+			if (firstframe->flags & RX_LOCAL)
+				*pflags |= MSG_DONTROUTE;
+			if (firstframe->flags & RX_OWN)
+				*pflags |= MSG_CONFIRM;
+
 			firstframe->flags &= BCM_CAN_FLAGS_MASK;
+		}
 	}
 
 	if (has_timestamp) {
@@ -360,7 +387,6 @@ static void bcm_send_to_user(struct bcm_op *op, struct bcm_msg_head *head,
 	 *  containing the interface index.
 	 */
 
-	sock_skb_cb_check_size(sizeof(struct sockaddr_can));
 	addr = (struct sockaddr_can *)skb->cb;
 	memset(addr, 0, sizeof(*addr));
 	addr->can_family  = AF_CAN;
@@ -444,7 +470,7 @@ static void bcm_rx_changed(struct bcm_op *op, struct canfd_frame *data)
 		op->frames_filtered = op->frames_abs = 0;
 
 	/* this element is not throttled anymore */
-	data->flags &= (BCM_CAN_FLAGS_MASK|RX_RECV);
+	data->flags &= ~RX_THR;
 
 	memset(&head, 0, sizeof(head));
 	head.opcode  = RX_CHANGED;
@@ -465,13 +491,17 @@ static void bcm_rx_changed(struct bcm_op *op, struct canfd_frame *data)
  */
 static void bcm_rx_update_and_send(struct bcm_op *op,
 				   struct canfd_frame *lastdata,
-				   const struct canfd_frame *rxdata)
+				   const struct canfd_frame *rxdata,
+				   unsigned char traffic_flags)
 {
 	memcpy(lastdata, rxdata, op->cfsiz);
 
 	/* mark as used and throttled by default */
 	lastdata->flags |= (RX_RECV|RX_THR);
 
+	/* add own/local/remote traffic flags */
+	lastdata->flags |= traffic_flags;
+
 	/* throttling mode inactive ? */
 	if (!op->kt_ival2) {
 		/* send RX_CHANGED to the user immediately */
@@ -508,7 +538,8 @@ static void bcm_rx_update_and_send(struct bcm_op *op,
  *                       received data stored in op->last_frames[]
  */
 static void bcm_rx_cmp_to_index(struct bcm_op *op, unsigned int index,
-				const struct canfd_frame *rxdata)
+				const struct canfd_frame *rxdata,
+				unsigned char traffic_flags)
 {
 	struct canfd_frame *cf = op->frames + op->cfsiz * index;
 	struct canfd_frame *lcf = op->last_frames + op->cfsiz * index;
@@ -521,7 +552,7 @@ static void bcm_rx_cmp_to_index(struct bcm_op *op, unsigned int index,
 
 	if (!(lcf->flags & RX_RECV)) {
 		/* received data for the first time => send update to user */
-		bcm_rx_update_and_send(op, lcf, rxdata);
+		bcm_rx_update_and_send(op, lcf, rxdata, traffic_flags);
 		return;
 	}
 
@@ -529,7 +560,7 @@ static void bcm_rx_cmp_to_index(struct bcm_op *op, unsigned int index,
 	for (i = 0; i < rxdata->len; i += 8) {
 		if ((get_u64(cf, i) & get_u64(rxdata, i)) !=
 		    (get_u64(cf, i) & get_u64(lcf, i))) {
-			bcm_rx_update_and_send(op, lcf, rxdata);
+			bcm_rx_update_and_send(op, lcf, rxdata, traffic_flags);
 			return;
 		}
 	}
@@ -537,7 +568,7 @@ static void bcm_rx_cmp_to_index(struct bcm_op *op, unsigned int index,
 	if (op->flags & RX_CHECK_DLC) {
 		/* do a real check in CAN frame length */
 		if (rxdata->len != lcf->len) {
-			bcm_rx_update_and_send(op, lcf, rxdata);
+			bcm_rx_update_and_send(op, lcf, rxdata, traffic_flags);
 			return;
 		}
 	}
@@ -644,6 +675,7 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
 	struct bcm_op *op = (struct bcm_op *)data;
 	const struct canfd_frame *rxframe = (struct canfd_frame *)skb->data;
 	unsigned int i;
+	unsigned char traffic_flags;
 
 	if (op->can_id != rxframe->can_id)
 		return;
@@ -673,15 +705,24 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
 		return;
 	}
 
+	/* compute flags to distinguish between own/local/remote CAN traffic */
+	traffic_flags = 0;
+	if (skb->sk) {
+		traffic_flags |= RX_LOCAL;
+		if (skb->sk == op->sk)
+			traffic_flags |= RX_OWN;
+	}
+
 	if (op->flags & RX_FILTER_ID) {
 		/* the easiest case */
-		bcm_rx_update_and_send(op, op->last_frames, rxframe);
+		bcm_rx_update_and_send(op, op->last_frames, rxframe,
+				       traffic_flags);
 		goto rx_starttimer;
 	}
 
 	if (op->nframes == 1) {
 		/* simple compare with index 0 */
-		bcm_rx_cmp_to_index(op, 0, rxframe);
+		bcm_rx_cmp_to_index(op, 0, rxframe, traffic_flags);
 		goto rx_starttimer;
 	}
 
@@ -698,7 +739,8 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
 			if ((get_u64(op->frames, 0) & get_u64(rxframe, 0)) ==
 			    (get_u64(op->frames, 0) &
 			     get_u64(op->frames + op->cfsiz * i, 0))) {
-				bcm_rx_cmp_to_index(op, i, rxframe);
+				bcm_rx_cmp_to_index(op, i, rxframe,
+						    traffic_flags);
 				break;
 			}
 		}
@@ -1675,6 +1717,9 @@ static int bcm_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 		memcpy(msg->msg_name, skb->cb, msg->msg_namelen);
 	}
 
+	/* assign the flags that have been recorded in bcm_send_to_user() */
+	msg->msg_flags |= *(bcm_flags(skb));
+
 	skb_free_datagram(sk, skb);
 
 	return size;