can: canxl: add virtual CAN network identifier support

CAN XL data frames contain an 8-bit virtual CAN network identifier (VCID).
A VCID value of zero represents an 'untagged' CAN XL frame.

To receive and send these optional VCIDs via CAN_RAW sockets a new socket
option CAN_RAW_XL_VCID_OPTS is introduced to define/access VCID content:

- tx: set the outgoing VCID value by the kernel (one fixed 8-bit value)
- tx: pass through VCID values from the user space (e.g. for traffic replay)
- rx: apply VCID receive filter (value/mask) to be passed to the user space

With the 'tx pass through' option CAN_RAW_XL_VCID_TX_PASS all valid VCID
values can be sent, e.g. to replay full qualified CAN XL traffic.

The VCID value provided for the CAN_RAW_XL_VCID_TX_SET option will
override the VCID value in the struct canxl_frame.prio defined for
CAN_RAW_XL_VCID_TX_PASS when both flags are set.

With a rx_vcid_mask of zero all possible VCID values (0x00 - 0xFF) are
passed to the user space when the CAN_RAW_XL_VCID_RX_FILTER flag is set.
Without this flag only untagged CAN XL frames (VCID = 0x00) are delivered
to the user space (default).

The 8-bit VCID is stored inside the CAN XL prio element (only in CAN XL
frames!) to not interfere with other CAN content or the CAN filters
provided by the CAN_RAW sockets and kernel infrastruture.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20240212213550.18516-1-socketcan@hartkopp.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

1 files changed, 7 insertions, 2 deletions

diff --git a/include/uapi/linux/can.h b/include/uapi/linux/can.h
index 939db2388208..e78cbd85ce7c 100644
--- a/include/uapi/linux/can.h
+++ b/include/uapi/linux/can.h
@@ -193,9 +193,14 @@ struct canfd_frame {
 #define CANXL_XLF 0x80 /* mandatory CAN XL frame flag (must always be set!) */
 #define CANXL_SEC 0x01 /* Simple Extended Content (security/segmentation) */
 
+/* the 8-bit VCID is optionally placed in the canxl_frame.prio element */
+#define CANXL_VCID_OFFSET 16 /* bit offset of VCID in prio element */
+#define CANXL_VCID_VAL_MASK 0xFFUL /* VCID is an 8-bit value */
+#define CANXL_VCID_MASK (CANXL_VCID_VAL_MASK << CANXL_VCID_OFFSET)
+
 /**
  * struct canxl_frame - CAN with e'X'tended frame 'L'ength frame structure
- * @prio:  11 bit arbitration priority with zero'ed CAN_*_FLAG flags
+ * @prio:  11 bit arbitration priority with zero'ed CAN_*_FLAG flags / VCID
  * @flags: additional flags for CAN XL
  * @sdt:   SDU (service data unit) type
  * @len:   frame payload length in byte (CANXL_MIN_DLEN .. CANXL_MAX_DLEN)
@@ -205,7 +210,7 @@ struct canfd_frame {
  * @prio shares the same position as @can_id from struct can[fd]_frame.
  */
 struct canxl_frame {
-	canid_t prio;  /* 11 bit priority for arbitration (canid_t) */
+	canid_t prio;  /* 11 bit priority for arbitration / 8 bit VCID */
 	__u8    flags; /* additional flags for CAN XL */
 	__u8    sdt;   /* SDU (service data unit) type */
 	__u16   len;   /* frame payload length in byte */