Re: [RFC] CAN FD support

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

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On 05/03/2012 02:38 PM, Oliver Hartkopp wrote:
[...]

>> I share this.
>> I'd even prefer u16 over u8 even.
>> No legacy issues exist when changing the meaning of can_dlc, since current
>> CAN frames have equal values for DLC & length!
>>
>>> the struct is also used by the app.
> 
> 
> Yes - that's the main problem IMO.
> 
> What about this binary compatible introduction of cf->len ...

...but it's not 100% source compatible, due to a compiler bug in gcc.
You cannot use C99 initializers on anonymous unions in certain gcc versions.

[..]

> --- a/include/linux/can.h
> +++ b/include/linux/can.h
> @@ -57,7 +57,10 @@ typedef __u32 can_err_mask_t;
>   */
>  struct can_frame {
>  	canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
> -	__u8    can_dlc; /* data length code: 0 .. 8 */
> +	union {
> +		__u8    can_dlc; /* data length code: 0 .. 8 */
> +		__u8    len; /* data length: 0 .. 8 */
> +	};
>  	__u8    data[8] __attribute__((aligned(8)));
>  };

Marc

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