can: remove CAN FD compatibility for CAN 2.0 sockets

In commit e2d265d3b587 (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>

diff --git a/Documentation/networking/can.txt b/Documentation/networking/can.txt
index f3089d4235153b6fa03aaf5c8d09c81043bba996..0cbe6ec22d6ff1d6a3c739f05ae61f4dc24781ec 100644 (file)
--- a/Documentation/networking/can.txt
+++ b/Documentation/networking/can.txt
@@ -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

diff --git a/net/can/raw.c b/net/can/raw.c
index 8be757cca2ec444171982cb8c33ef58ab27310be..081e81fd017fa53f7a6ed3afd341601b43377531 100644 (file)
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -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) {