Commit 821047c4 authored by Oliver Hartkopp's avatar Oliver Hartkopp Committed by Marc Kleine-Budde
Browse files

can: remove CAN FD compatibility for CAN 2.0 sockets 



In commit e2d265d3 (canfd: add support for CAN FD in CAN_RAW sockets)
CAN FD frames with a payload length up to 8 byte are passed to legacy
sockets where the CAN FD support was not enabled by the application.

After some discussions with developers at a fair this well meant feature
leads to confusion as no clean switch for CAN / CAN FD is provided to the
application programmer. Additionally a compatibility like this for legacy
CAN_RAW sockets requires some compatibility handling for the sending, e.g.
make CAN2.0 frames a CAN FD frame with BRS at transmission time (?!?).

This will become a mess when people start to develop applications with
real CAN FD hardware. This patch reverts the bad compatibility code
together with the documentation describing the removed feature.

Acked-by: default avatarStephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: default avatarOliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: default avatarMarc Kleine-Budde <mkl@pengutronix.de>
parent 4b5b8227

Documentation/networking/can.txt

+0 −6
Original line number Diff line number Diff line
@@ -554,12 +554,6 @@ solution for a couple of reasons: 
  not specified in the struct can_frame and therefore it is only valid in

  CANFD_MTU sized CAN FD frames.



  As long as the payload length is <=8 the received CAN frames from CAN FD

  capable CAN devices can be received and read by legacy sockets too. When

  user-generated CAN FD frames have a payload length <=8 these can be send

  by legacy CAN network interfaces too. Sending CAN FD frames with payload

  length > 8 to a legacy CAN network interface returns an -EMSGSIZE error.



  Implementation hint for new CAN applications:



  To build a CAN FD aware application use struct canfd_frame as basic CAN

net/can/raw.c

+5 −21
Original line number Diff line number Diff line
@@ -121,13 +121,9 @@ static void raw_rcv(struct sk_buff *oskb, void *data) 
	if (!ro->recv_own_msgs && oskb->sk == sk)

		return;



	/* do not pass frames with DLC > 8 to a legacy socket */

	if (!ro->fd_frames) {

		struct canfd_frame *cfd = (struct canfd_frame *)oskb->data;



		if (unlikely(cfd->len > CAN_MAX_DLEN))

	/* do not pass non-CAN2.0 frames to a legacy socket */

	if (!ro->fd_frames && oskb->len != CAN_MTU)

		return;

	}



	/* clone the given skb to be able to enqueue it into the rcv queue */

	skb = skb_clone(oskb, GFP_ATOMIC);
@@ -738,9 +734,7 @@ static int raw_recvmsg(struct kiocb *iocb, struct socket *sock, 
		       struct msghdr *msg, size_t size, int flags)

{

	struct sock *sk = sock->sk;

	struct raw_sock *ro = raw_sk(sk);

	struct sk_buff *skb;

	int rxmtu;

	int err = 0;

	int noblock;
@@ -751,20 +745,10 @@ static int raw_recvmsg(struct kiocb *iocb, struct socket *sock, 
	if (!skb)

		return err;



	/*

	 * when serving a legacy socket the DLC <= 8 is already checked inside

	 * raw_rcv(). Now check if we need to pass a canfd_frame to a legacy

	 * socket and cut the possible CANFD_MTU/CAN_MTU length to CAN_MTU

	 */

	if (!ro->fd_frames)

		rxmtu = CAN_MTU;

	else

		rxmtu = skb->len;



	if (size < rxmtu)

	if (size < skb->len)

		msg->msg_flags |= MSG_TRUNC;

	else

		size = rxmtu;

		size = skb->len;



	err = memcpy_toiovec(msg->msg_iov, skb->data, size);

	if (err < 0) {

CRA Git | Maintained and supported by SUSTech CRA and CCSE