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>

1 files changed, 5 insertions, 21 deletions

diff --git a/net/can/raw.c b/net/can/raw.c
index 8be757cca2ec..081e81fd017f 100644
--- 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) {