[PATCH v2] can: bcm: add recvmsg flags for own, local and remote traffic

From: Nicolas Maier
Date: Sun Jan 14 2024 - 09:08:26 EST

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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@xxxxxxxxx>
---

v2:
* add 'traffic_flags' parameter to bcm_rx_update_and_send and
bcm_rx_cmp_to_index, to put the flags in the can frame after its data
has been copied

Documentation/networking/can.rst | 34 +++++++++--------
net/can/bcm.c | 65 ++++++++++++++++++++++++++------
2 files changed, 72 insertions(+), 27 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..8c0468823911 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;
@@ -465,13 +489,17 @@ 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 +536,8 @@ 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 +550,7 @@ 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 +558,7 @@ 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 +566,7 @@ 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 +673,7 @@ 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 +703,24 @@ 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 +737,8 @@ 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 +1715,9 @@ 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

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