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can: remove CAN FD compatibility for CAN 2.0 sockets 

In commit e2d265d3b5 (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: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This commit is contained in:
Oliver Hartkopp 2014-03-01 15:31:53 +01:00 committed by Marc Kleine-Budde
parent 4b5b82274a
commit 821047c405
2 changed files with 5 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
Documentation/networking/can.txt
View File

@ -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

26
net/can/raw.c
View File

@ -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))
return;
}
/* 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) {