Re: More flags for logging

[Marc Kleine-Budde <mkl@pengutronix.de>]

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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.

> 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

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
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