On 03.05.21 12:08, Marc Kleine-Budde wrote:
On 03.05.2021 12:02:46, Marc Kleine-Budde wrote:
The SocketCAN API is a great initiative for standardizing the CAN
interface API. This request tries to extend this initiative for more use
cases.
Context:
The SocketCAN was adopted by libpcap and tcpdump as the standard format
for logging CAN Frames in PCAP and PCAP-NG. See:
https://www.tcpdump.org/linktypes/LINKTYPE_CAN_SOCKETCAN.html
https://github.com/wireshark/wireshark/blob/master/epan/dissectors/packet-socketcan.c
https://www.wireshark.org/docs/dfref/c/can.html
Problem:
Applications that perform logging, usually need more details that normal
applications, for the sake of debugging later on. Flags needs to be
reserved/allocated in the SocketCAN API, so that logging applications
can make use of them in the PCAP format. The flags does not need
necessary need to be implemented by SocketCAN, they just need to be
marked as reserved for such use case.
Needed Flags:
FDF Flag
- Since CAN Frames and CAN-FD frames can co-exist in the same bus,
logging application needs to know if a normal CAN Frame was
transmitted on a CAN-FD bus, namely was the FDF bit set or not.
I think someone asked for that some time ago. But that was never
mainlined. I'll look for that old mail.
When you display CAN and CAN FD frames in Wireshark they are displayed
as different "protocols" - as they also have different ethtypes.
So the difference is provided by the 'protocol' field. Or did I miss
something?
Regards,
Oliver
ACK bit in data frame
- Some logging hardware can act as a "spy", meaning that it records CAN
Frames, but does not set the ACK bit
- A way to know for a given frame (FD or not), was the ACK bit set or
not.
- Current API allow detecting missing ACK, but it does not report what
Frame had a missing ACK.
This means the driver has to set a flag if it's configured in
listen-only mode. That should be possible.
I think we can make use of flags in the struct canfd_frame for this:
| struct canfd_frame {
| canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
| __u8 len; /* frame payload length in byte */
| __u8 flags; /* additional flags for CAN FD */
| __u8 __res0; /* reserved / padding */
| __u8 __res1; /* reserved / padding */
| __u8 data[CANFD_MAX_DLEN] __attribute__((aligned(8)));
| };
The struct can_frame doesn't have the flags member yet, but we can add
it there.
regards,
Marc
