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

[Stefano Garzarella]

On Sun, Jun 14, 2026 at 08:47:56PM +0300, Arseniy Krasnov wrote:
>Logically it was based on TCP implementation, so make further support
>easier, rewrite it in the TCP way.

Hi Arseniy, and thank you so much for the patch!

I’d like to ask you to expand on the message a bit, especially to 
explain why we’re making this change.

In particular, I’d like to better understand whether this is just a 
cosmetic change or if we’re fixing any issues (and if so, which ones), 
so we can determine whether this patch should be backported to the 
stable branches.

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

Ah, okay is net-next material, please use the net-next tag (ie. [PATCH 
net-next v2]).

>
> 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);
>

nit: we can remove this extra blank line.

For the rest I can't see anything wrong, but a bit more context in the 
commit would help me in the review.

Thanks,
Stefano