Hi Ayoub,
On 04.05.21 11:49, Ayoub Kaanich wrote:
There seems to be a mis-conception about how WireShark/Libpcap handle SocketCAN:
There is no ethertype involved, the data of the frame will directly start with the CAN ID.
The socket CAN in PCAP format pre-date CAN-FD (Developed in 2011), so at the time, there was only "CAN" (Introduced in Oct, 2009).
See https://github.com/the-tcpdump-group/libpcap/commit/86ed15cc8b4bd7dc1458559108e66a07ec6721ec
The introduction of CAN-FD later on did not change that.
Ah, now I got the problem.
I was heavily involved in introducing CAN FD into Wireshark here:
https://github.com/wireshark/wireshark/commit/7fad354a3e379382368cd1ef67b841315c29e050#diff-f0fd5f515da65110cd5c1231b43180693e1d46779765d65c997e32da11ae70d1
But this obviously had NO impact on libpcap :-/
Libpcap library maps both LINUX_SLL_P_CAN and LINUX_SLL_P_CANFD (they are treated identically the same way) to DLT_CAN_SOCKETCAN and copy bytes as is (the only change is changing the endianness if ID if needed).
So this would mean, we need a separate handler for LINUX_SLL_P_CANFD ??
Best regards,
Oliver
The MTU solution still not does provide a fix for the case of a normal CAN message being transported over a CAN-FD bus.
In this case, application cannot tell if frame was physically transported as CAN or CAN-FD.
See https://noelscher.com/blog/posts/compatibility-of-can-and-can-fd/
Best Regards.
Ayoub Kaanich.
-----Original Message-----
From: mailto:socketcan@xxxxxxxxxxxx
Sent: Tuesday, May 4, 2021 10:49 AM
To: mailto:mkl@xxxxxxxxxxxxxx; mailto:linux-can@xxxxxxxxxxxxxxx
Cc: mailto:kayoub5@xxxxxxxx
Subject: Re: More flags for logging
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/pa
cket-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
