The different CAN frame types are defined by Linux SLL_P types in the
sll_protocol field and the length of the frame.
LINUX_SLL_P_CANXL:
The frame length for CAN XL can be 12 + 1 to 12 + 2048 (13 .. 2060) byte.
Additionally the CANXL_XLF flag has to be set.
LINUX_SLL_P_CAN and LINUX_SLL_P_CANFD:
The frame length for CAN CC is 16 byte and for CAN FD it is 72 byte.
Additionally the CANXL_XLF flag is cleared in CAN CC/FD frames.
Simplify the CAN packet type detection by checking exactly the above
rules without checking the CANFD_FDF flag which is not guarantied
over all Linux kernel versions.
Signed-off-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
---
epan/dissectors/packet-socketcan.c | 56 +++++-------------------------
1 file changed, 8 insertions(+), 48 deletions(-)
diff --git a/epan/dissectors/packet-socketcan.c b/epan/dissectors/packet-socketcan.c
index e441c44ade..e9fcdb2dd8 100644
--- a/epan/dissectors/packet-socketcan.c
+++ b/epan/dissectors/packet-socketcan.c
@@ -110,10 +110,11 @@ static heur_dtbl_entry_t *heur_dtbl_entry;
#define CANFD_FLAG_OFFSET 5
#define CANFD_BRS 0x01 /* bit rate switch (second bitrate for payload data) */
#define CANFD_ESI 0x02 /* error state indicator of the transmitting node */
+#define CANXL_FLAGS_OFFSET CAN_LEN_OFFSET
#define CANXL_LEN_OFFSET 6
#define CANXL_DATA_OFFSET 12
static dissector_table_t can_id_dissector_table = NULL;
static dissector_table_t can_extended_id_dissector_table = NULL;
@@ -589,69 +590,28 @@ dissect_socketcan_common(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, gu
static int * const canxl_flag_fields[] = {
&hf_canxl_secflag,
NULL,
};
- /*
- * If we weren't told the type of this frame, check
- * whether the CANFD_FDF flag is set in the FD flags
- * field of the header; if so, it's a CAN FD frame.
- * otherwise, it's a CAN frame.
- *
- * However, trust the CANFD_FDF flag only if the only
- * bits set in the FD flags field are the known bits,
- * and the two bytes following that field are both
- * zero. This is because some older LINKTYPE_CAN_SOCKETCAN
- * frames had uninitialized junk in the FD flags field,
- * so we treat a frame with what appears to be uninitialized
- * junk as being CAN rather than CAN FD, under the assumption
- * that the CANFD_FDF bit is set because the field is
- * uninitialized, not because it was explicitly set because
- * it's a CAN FD frame. At least some newer code that sets
- * that flag also makes sure that the fields in question are
- * initialized, so we assume that if they're not initialized
- * the code is older code that didn't support CAN FD.
- */
+ /* determine CAN packet type */
if (can_packet_type == PACKET_TYPE_UNKNOWN) {
- guint8 frame_length;
- guint8 fd_flags;
+ guint8 canxl_flags;
/*
* Check whether the frame has the CANXL_XLF flag set in what
* is in the location of the frame length field of a CAN classic
* or CAN FD frame; if so, then it's a CAN XL frame (and that
* field is the flags field of that frame).
*/
- frame_length = tvb_get_guint8(tvb, CAN_LEN_OFFSET);
- if (frame_length & CANXL_XLF) {
+ canxl_flags = tvb_get_guint8(tvb, CANXL_FLAGS_OFFSET);
+ if ((tvb_reported_length(tvb) > 12) && (canxl_flags & CANXL_XLF)) {
can_packet_type = PACKET_TYPE_CAN_XL;
} else {
- /*
- * This is a CAN classic or CAN FD frame.
- * Check whether the flags field has the CANFD_FDF
- * flag set, has no unknown flag bits set, and has
- * no bits set in the two reserved fields. If so,
- * it's a CAN FD frame; otherwise, it's either a
- * CAN classic frame, or a frame where the CANFD_FDF
- * flag is set but where that might just be because
- * that field contains uninitialized junk rather
- * than because it's a CAN FD frame, so we treat it
- * as a CAN classic frame.
- */
- fd_flags = tvb_get_guint8(tvb, CANFD_FLAG_OFFSET);
-
- if ((fd_flags & CANFD_FDF) &&
- ((fd_flags & ~(CANFD_BRS | CANFD_ESI | CANFD_FDF)) == 0) &&
- tvb_get_guint8(tvb, CANFD_FLAG_OFFSET + 1) == 0 &&
- tvb_get_guint8(tvb, CANFD_FLAG_OFFSET + 2) == 0) {
+ if (tvb_reported_length(tvb) == 72)
can_packet_type = PACKET_TYPE_CAN_FD;
- } else {
- if (tvb_reported_length(tvb) == 72)
- can_packet_type = PACKET_TYPE_CAN_FD;
- else
- can_packet_type = PACKET_TYPE_CAN;
- }
+ else if (tvb_reported_length(tvb) == 16)
+ can_packet_type = PACKET_TYPE_CAN;
}
}
can_info.bus_id = get_bus_id(pinfo);
--
2.43.0
