[PATCH v2] vsock/virtio: rework MSG_ZEROCOPY flag handling

[Arseniy Krasnov]

Logically it was based on TCP implementation, so make further support
easier, rewrite it in the TCP way.

Signed-off-by: Arseniy Krasnov <avkrasnov@xxxxxxxxx>
---
 Changelog v1->v2:
 * Rebase on last 'net-next'. Don't need 'skb_zcopy_set()' now - it was
   already added.

 net/vmw_vsock/virtio_transport_common.c | 48 ++++++++++++-------------
 1 file changed, 23 insertions(+), 25 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 09475007165b..787524b8cb44 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -328,38 +328,36 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 	if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
 		return pkt_len;
 
-	if (info->msg) {
-		/* If zerocopy is not enabled by 'setsockopt()', we behave as
-		 * there is no MSG_ZEROCOPY flag set.
+	if (info->msg && (info->msg->msg_flags & MSG_ZEROCOPY)) {
+		/* If 'info->msg' is not NULL, this is only VIRTIO_VSOCK_OP_RW.
+		 * 'MSG_ZEROCOPY' flag handling here is based on the same flag
+		 * handling from 'tcp_sendmsg_locked()'.
 		 */
-		if (!sock_flag(sk_vsock(vsk), SOCK_ZEROCOPY))
-			info->msg->msg_flags &= ~MSG_ZEROCOPY;
+		if (info->msg->msg_ubuf) {
+			uarg = info->msg->msg_ubuf;
+			can_zcopy = virtio_transport_can_zcopy(t_ops, info, pkt_len);
+		} else if (sock_flag(sk_vsock(vsk), SOCK_ZEROCOPY)) {
+			uarg = msg_zerocopy_realloc(sk_vsock(vsk), pkt_len,
+						    NULL, false);
+			if (!uarg) {
+				virtio_transport_put_credit(vvs, pkt_len);
+				return -ENOMEM;
+			}
 
-		if (info->msg->msg_flags & MSG_ZEROCOPY)
 			can_zcopy = virtio_transport_can_zcopy(t_ops, info, pkt_len);
 
+			if (!can_zcopy)
+				uarg_to_msgzc(uarg)->zerocopy = 0;
+
+			have_uref = true;
+		}
+
+		/* 'can_zcopy' means that this transmission will be
+		 * in zerocopy way (e.g. using 'frags' array).
+		 */
 		if (can_zcopy)
 			max_skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE,
 					    (MAX_SKB_FRAGS * PAGE_SIZE));
-
-		if (info->msg->msg_flags & MSG_ZEROCOPY &&
-		    info->op == VIRTIO_VSOCK_OP_RW) {
-			uarg = info->msg->msg_ubuf;
-
-			if (!uarg) {
-				uarg = msg_zerocopy_realloc(sk_vsock(vsk),
-							    pkt_len, NULL, false);
-				if (!uarg) {
-					virtio_transport_put_credit(vvs, pkt_len);
-					return -ENOMEM;
-				}
-
-				if (!can_zcopy)
-					uarg_to_msgzc(uarg)->zerocopy = 0;
-
-				have_uref = true;
-			}
-		}
 	}
 
 	rest_len = pkt_len;
-- 
2.25.1