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Date: Sun, 7 Jan 2024 07:44:27 +0100
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From: Nicolas Maier <nicolas.maier.dev@gmail.com>
Subject: [PATCH] can: bcm: add recvmsg flags for own, local and remote traffic
To: socketcan@hartkopp.net, mkl@pengutronix.de, linux-can@vger.kernel.org
Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
 pabeni@redhat.com, corbet@lwn.net, netdev@vger.kernel.org,
 linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
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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 1e55659ce6dd ("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>
---
 Documentation/networking/can.rst | 34 ++++++++++++++------------
 net/can/bcm.c                    | 42 +++++++++++++++++++++++++++++---
 2 files changed, 56 insertions(+), 20 deletions(-)

diff --git a/Documentation/networking/can.rst b/Documentation/networking/can.rst
index d7e1ada905b2..62519d38c58b 100644
--- a/Documentation/networking/can.rst
+++ b/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)
 -----------------------------------------------
 
diff --git a/net/can/bcm.c b/net/can/bcm.c
index 9168114fc87f..32345e155006 100644
--- a/net/can/bcm.c
+++ b/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 +140,19 @@ 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)
+{
+	sock_skb_cb_check_size(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 bcm_sock *bcm_sk(const struct sock *sk)
 {
 	return (struct bcm_sock *)sk;
@@ -325,6 +340,7 @@ 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)
@@ -344,8 +360,16 @@ 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) {
+			pflags = bcm_flags(skb);
+			*pflags = 0;
+			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) {
@@ -444,7 +468,7 @@ 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;
@@ -642,7 +666,7 @@ static enum hrtimer_restart bcm_rx_thr_handler(struct hrtimer *hrtimer)
 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;
+	struct canfd_frame *rxframe = (struct canfd_frame *)skb->data;
 	unsigned int i;
 
 	if (op->can_id != rxframe->can_id)
@@ -657,6 +681,13 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
 			return;
 	}
 
+	/* add flags to distinguish between own/local/remote CAN traffic */
+	if (skb->sk) {
+		rxframe->flags |= RX_LOCAL;
+		if (skb->sk == op->sk)
+			rxframe->flags |= RX_OWN;
+	}
+
 	/* disable timeout */
 	hrtimer_cancel(&op->timer);
 
@@ -1675,6 +1706,9 @@ 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;
-- 
2.34.1