[PATCH v8 3/7] can: set CANFD_FDF flag in all CAN FD frame structures

[Oliver Hartkopp <socketcan@hartkopp.net>]

To simplify the testing in user space all struct canfd_frame's provided by
the CAN subsystem of the Linux kernel now have the CANFD_FDF flag set in
canfd_frame::flags.

NB: Handcrafted ETH_P_CANFD frames introduced via PF_PACKET socket might
not set this bit correctly. During the check for sufficient headroom in
PF_PACKET sk_buffs the uninitialized CAN sk_buff data structures are filled.
In the case of a CAN FD frame the CANFD_FDF flag is set accordingly.

As the CAN frame content is already zero initialized in alloc_canfd_skb()
the obsolete initialization of cf->flags in the CTU CAN FD driver has been
removed as it would overwrite the already set CANFD_FDF flag.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 drivers/net/can/ctucanfd/ctucanfd_base.c |  1 -
 drivers/net/can/dev/skb.c                | 11 +++++++++++
 include/uapi/linux/can.h                 |  4 ++--
 net/can/af_can.c                         |  5 +++++
 4 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/net/can/ctucanfd/ctucanfd_base.c b/drivers/net/can/ctucanfd/ctucanfd_base.c
index 3c18d028bd8c..c4026712ab7d 100644
--- a/drivers/net/can/ctucanfd/ctucanfd_base.c
+++ b/drivers/net/can/ctucanfd/ctucanfd_base.c
@@ -655,11 +655,10 @@ static void ctucan_read_rx_frame(struct ctucan_priv *priv, struct canfd_frame *c
 		cf->can_id = (idw & CAN_EFF_MASK) | CAN_EFF_FLAG;
 	else
 		cf->can_id = (idw >> 18) & CAN_SFF_MASK;
 
 	/* BRS, ESI, RTR Flags */
-	cf->flags = 0;
 	if (FIELD_GET(REG_FRAME_FORMAT_W_FDF, ffw)) {
 		if (FIELD_GET(REG_FRAME_FORMAT_W_BRS, ffw))
 			cf->flags |= CANFD_BRS;
 		if (FIELD_GET(REG_FRAME_FORMAT_W_ESI_RSV, ffw))
 			cf->flags |= CANFD_ESI;
diff --git a/drivers/net/can/dev/skb.c b/drivers/net/can/dev/skb.c
index b896e1ce3b47..adb413bdd734 100644
--- a/drivers/net/can/dev/skb.c
+++ b/drivers/net/can/dev/skb.c
@@ -242,10 +242,13 @@ struct sk_buff *alloc_canfd_skb(struct net_device *dev,
 	can_skb_prv(skb)->ifindex = dev->ifindex;
 	can_skb_prv(skb)->skbcnt = 0;
 
 	*cfd = skb_put_zero(skb, sizeof(struct canfd_frame));
 
+	/* set CAN FD flag by default */
+	(*cfd)->flags = CANFD_FDF;
+
 	return skb;
 }
 EXPORT_SYMBOL_GPL(alloc_canfd_skb);
 
 struct sk_buff *alloc_can_err_skb(struct net_device *dev, struct can_frame **cf)
@@ -285,10 +288,18 @@ static bool can_skb_headroom_valid(struct net_device *dev, struct sk_buff *skb)
 			skb->pkt_type = PACKET_HOST;
 
 		skb_reset_mac_header(skb);
 		skb_reset_network_header(skb);
 		skb_reset_transport_header(skb);
+
+		/* set CANFD_FDF flag for CAN FD frames */
+		if (can_is_canfd_skb(skb)) {
+			struct canfd_frame *cfd;
+
+			cfd = (struct canfd_frame *)skb->data;
+			cfd->flags |= CANFD_FDF;
+		}
 	}
 
 	return true;
 }
 
diff --git a/include/uapi/linux/can.h b/include/uapi/linux/can.h
index 90801ada2bbe..7b23eeeb3273 100644
--- a/include/uapi/linux/can.h
+++ b/include/uapi/linux/can.h
@@ -139,12 +139,12 @@ struct can_frame {
  * The struct can_frame and struct canfd_frame intentionally share the same
  * layout to be able to write CAN frame content into a CAN FD frame structure.
  * When this is done the former differentiation via CAN_MTU / CANFD_MTU gets
  * lost. CANFD_FDF allows programmers to mark CAN FD frames in the case of
  * using struct canfd_frame for mixed CAN / CAN FD content (dual use).
- * N.B. the Kernel APIs do NOT provide mixed CAN / CAN FD content inside of
- * struct canfd_frame therefore the CANFD_FDF flag is disregarded by Linux.
+ * Since the introduction of CAN XL the CANFD_FDF flag is set in all CAN FD
+ * frame structures provided by the CAN subsystem of the Linux kernel.
  */
 #define CANFD_BRS 0x01 /* bit rate switch (second bitrate for payload data) */
 #define CANFD_ESI 0x02 /* error state indicator of the transmitting node */
 #define CANFD_FDF 0x04 /* mark CAN FD for dual use of struct canfd_frame */
 
diff --git a/net/can/af_can.c b/net/can/af_can.c
index afa6c2151bc4..072a6a5c9dd1 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -203,11 +203,16 @@ int can_send(struct sk_buff *skb, int loop)
 	int err = -EINVAL;
 
 	if (can_is_can_skb(skb)) {
 		skb->protocol = htons(ETH_P_CAN);
 	} else if (can_is_canfd_skb(skb)) {
+		struct canfd_frame *cfd = (struct canfd_frame *)skb->data;
+
 		skb->protocol = htons(ETH_P_CANFD);
+
+		/* set CAN FD flag for CAN FD frames by default */
+		cfd->flags |= CANFD_FDF;
 	} else {
 		goto inval_skb;
 	}
 
 	/* Make sure the CAN frame can pass the selected CAN netdevice. */
-- 
2.30.2