linux-kernel - Re: [RFC PATCH v1 2/4] virtio/vsock: support MSG_PEEK for SOCK

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Date:   Mon, 26 Jun 2023 18:28:31 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseniy Krasnov <AVKrasnov@...rdevices.ru>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Bobby Eshleman <bobby.eshleman@...edance.com>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...rdevices.ru, oxffffaa@...il.com
Subject: Re: [RFC PATCH v1 2/4] virtio/vsock: support MSG_PEEK for
 SOCK_SEQPACKET

On Sun, Jun 18, 2023 at 09:24:49AM +0300, Arseniy Krasnov wrote:
>This adds support of MSG_PEEK flag for SOCK_SEQPACKET type of socket.
>Difference with SOCK_STREAM is that this callback returns either length
>of the message or error.
>
>Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
>---
> net/vmw_vsock/virtio_transport_common.c | 63 +++++++++++++++++++++++--
> 1 file changed, 60 insertions(+), 3 deletions(-)
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index 2ee40574c339..352d042b130b 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -460,6 +460,63 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> 	return err;
> }
>
>+static ssize_t
>+virtio_transport_seqpacket_do_peek(struct vsock_sock *vsk,
>+				   struct msghdr *msg)
>+{
>+	struct virtio_vsock_sock *vvs = vsk->trans;
>+	struct sk_buff *skb;
>+	size_t total, len;
>+
>+	spin_lock_bh(&vvs->rx_lock);
>+
>+	if (!vvs->msg_count) {
>+		spin_unlock_bh(&vvs->rx_lock);
>+		return 0;
>+	}
>+
>+	total = 0;
>+	len = msg_data_left(msg);
>+
>+	skb_queue_walk(&vvs->rx_queue, skb) {
>+		struct virtio_vsock_hdr *hdr;
>+
>+		if (total < len) {
>+			size_t bytes;
>+			int err;
>+
>+			bytes = len - total;
>+			if (bytes > skb->len)
>+				bytes = skb->len;
>+
>+			spin_unlock_bh(&vvs->rx_lock);
>+
>+			/* sk_lock is held by caller so no one else can dequeue.
>+			 * Unlock rx_lock since memcpy_to_msg() may sleep.
>+			 */
>+			err = memcpy_to_msg(msg, skb->data, bytes);
>+			if (err)
>+				return err;
>+
>+			spin_lock_bh(&vvs->rx_lock);
>+		}
>+
>+		total += skb->len;
>+		hdr = virtio_vsock_hdr(skb);
>+
>+		if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOM) {
>+			if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOR)
>+				msg->msg_flags |= MSG_EOR;
>+
>+			break;
>+		}
>+	}
>+
>+	spin_unlock_bh(&vvs->rx_lock);
>+
>+	return total;

Should we return the minimum between total and len?

Thanks,
Stefano

>+}
>+
> static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
> 						 struct msghdr *msg,
> 						 int flags)
>@@ -554,9 +611,9 @@ virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
> 				   int flags)
> {
> 	if (flags & MSG_PEEK)
>-		return -EOPNOTSUPP;
>-
>-	return virtio_transport_seqpacket_do_dequeue(vsk, msg, flags);
>+		return virtio_transport_seqpacket_do_peek(vsk, msg);
>+	else
>+		return virtio_transport_seqpacket_do_dequeue(vsk, msg, flags);
> }
> EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_dequeue);
>
>-- 
>2.25.1
>