Hi, One solution is to mark a flag bit as 1/0 depending whether the frame was received using LINUX_SLL_P_CAN or LINUX_SLL_P_CANFD. This may solve 90% of the cases, but I don't think it's the solution we want to go with, since it does not cover classical CAN over CAN-FD transmission. See https://www.can-cia.org/fileadmin/resources/documents/proceedings/2015_esparza.pdf https://can-newsletter.org/uploads/media/raw/35a48f1d88ddf2a198638c0a5be51761.pdf I believe it would be better to have an FDF bit in the SocketCAN flags, that maps to (for example) MCP251XFD_OBJ_FLAGS_FDF Best Regards. -----Original Message----- From: Oliver Hartkopp <socketcan@xxxxxxxxxxxx> Sent: Tuesday, May 4, 2021 12:14 PM To: Ayoub Kaanich <ayoub.kaanich@xxxxxxxxxxxxxxxxxxxxxxx>; mkl@xxxxxxxxxxxxxx; linux-can@xxxxxxxxxxxxxxx Subject: Re: More flags for logging CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe. 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/86ed15cc8b4bd7dc14 > 58559108e66a07ec6721ec 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/p >>> a 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 >> >
