[RFC PATCH v3 08/17] vsock: check for MSG_ZEROCOPY support

[Arseniy Krasnov]

This feature totally depends on transport, so if transport doesn't
support it, return error.

Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
---
 include/net/af_vsock.h   | 7 +++++++
 net/vmw_vsock/af_vsock.c | 6 ++++++
 2 files changed, 13 insertions(+)

diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
index 0e7504a42925..ec09edc5f3a0 100644
--- a/include/net/af_vsock.h
+++ b/include/net/af_vsock.h
@@ -177,6 +177,9 @@ struct vsock_transport {
 
 	/* Read a single skb */
 	int (*read_skb)(struct vsock_sock *, skb_read_actor_t);
+
+	/* Zero-copy. */
+	bool (*msgzerocopy_allow)(void);
 };
 
 /**** CORE ****/
@@ -243,4 +246,8 @@ static inline void __init vsock_bpf_build_proto(void)
 {}
 #endif
 
+static inline bool vsock_msgzerocopy_allow(const struct vsock_transport *t)
+{
+	return t->msgzerocopy_allow && t->msgzerocopy_allow();
+}
 #endif /* __AF_VSOCK_H__ */
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index b2da791d920b..dbfe82ee7769 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1824,6 +1824,12 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
 		goto out;
 	}
 
+	if (msg->msg_flags & MSG_ZEROCOPY &&
+	    !vsock_msgzerocopy_allow(transport)) {
+		err = -EOPNOTSUPP;
+		goto out;
+	}
+
 	/* Wait for room in the produce queue to enqueue our user's data. */
 	timeout = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
 
-- 
2.25.1