Hello Marc, On 2021-07-29 12:55, Marc Kleine-Budde wrote: > On 29.07.2021 12:03:56, thomas@xxxxxxxxxxxxx wrote: >> Shouldn't the error only be returned if the >> canfd_frame I pass has more than 8 bytes when the interface is not in >> FD-mode? > > A CAN-2.0 frame with 8 bytes is something different than a CAN-FD frame > with 8 bytes. The kernel uses the length of the frame to decide if it is > a CAN-2.0 or CAN-FD frame. If your CAN controller has switched CAN-FD > off, it cannot send CAN-FD frames, thus you get an error. > > Does that make sense? Sure! I see how a CAN-2.0 frame with 8 bytes differs from a CAN-FD frame with 8-bytes, but when I receive into a canfd_frame I can't differentiate like that anymore. In userspace an 8B CAN-2.0 frame and an 8B CAN-FD frame look just the same, no matter the interface running with FD on or off. ... which is wrong as I just noticed. Paying attention to the actual bytes read by the socket I can see the 16 vs. 72B that make up a can_frame vs. a canfd_frame respectively. Even when always writing into a canfd_frame. The same differentiation I must make when sending... Thanks for the quick reply! Best regards Thomas Wagner
