[PATCH] can: raw: add missing error queue support

[Vincent Mailhol]

Error queue are not yet implemented in CAN-raw sockets.

The problem: a userland call to recvmsg(soc, msg, MSG_ERRQUEUE) on a
CAN-raw socket would unqueue messages from the normal queue without
any kind of error or warning. As such, it prevented CAN drivers from
using the functionalities that relies on the error queue such as
skb_tx_timestamp().

SCM_CAN_RAW_ERRQUEUE is defined as the type for the CAN raw error
queue. SCM stands for "Socket control messages". The name is inspired
from SCM_J1939_ERRQUEUE of include/uapi/linux/can/j1939.h.

Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
---
 include/uapi/linux/can/raw.h | 3 +++
 net/can/raw.c                | 4 ++++
 2 files changed, 7 insertions(+)

diff --git a/include/uapi/linux/can/raw.h b/include/uapi/linux/can/raw.h
index 6a11d308eb5c..3386aa81fdf2 100644
--- a/include/uapi/linux/can/raw.h
+++ b/include/uapi/linux/can/raw.h
@@ -49,6 +49,9 @@
 #include <linux/can.h>
 
 #define SOL_CAN_RAW (SOL_CAN_BASE + CAN_RAW)
+enum {
+	SCM_CAN_RAW_ERRQUEUE = 1,
+};
 
 /* for socket options affecting the socket (not the global system) */
 
diff --git a/net/can/raw.c b/net/can/raw.c
index 94a9405658dc..98abab119136 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -804,6 +804,10 @@ static int raw_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 	noblock =  flags & MSG_DONTWAIT;
 	flags   &= ~MSG_DONTWAIT;
 
+	if (flags & MSG_ERRQUEUE)
+		return sock_recv_errqueue(sk, msg, size,
+					  SOL_CAN_RAW, SCM_CAN_RAW_ERRQUEUE);
+
 	skb = skb_recv_datagram(sk, flags, noblock, &err);
 	if (!skb)
 		return err;
-- 
2.26.2