Re: Usb to can driver

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

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On 04/24/2013 07:40 PM, Oliver Hartkopp wrote:
>>> assumptions that are made:
>>> * The sizes of the struct can_frame members are id:u32 dlc:u8 data:u64 .
>>> * It is also assumed that existing defines like CAN_EFF_FLAG in can.h
>>> and can/error.h don't change, as they are used by the device to
>>> construct the can_id field.
>>
>> You cannot rely in your firmware, that the struct can_frame and
>> CAN_*_FLAG doesn't change. Please define your own struct.
>>
> 
> 
> Hm - i really appreciate the memcopy-only approach which can cope with the
> host byte order directly. This is a real improvement on the host side.
> 
> The struct can_frame and the error message content is official Kernel API and
> therefore can be assumed to be fix.

Yes but no. The struct can_frame to the _userspace_ is official Kernel
API/ABI, but within the kernel the is no stable API (see
stable_api_nonsense.txt). But if we go this way we should make compile
time checks, so that the compilation breaks if the struct can_frame changes.

> Btw. extensions like the introduction of the struct canfd_frame can always
> take place. But this comes along with really new functionality then.

> I would like to continue with the memcopy approach - but we probably need some
> frame type identifier to be able to handle different host CAN frames, like
> struct can_frame and struct canfd_frame, ...

Marc
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