Re: [RFC PATCH v1 2/4] virtio/vsock: support MSG_PEEK for SOCK_SEQPACKET

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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@xxxxxxxxxxxxxx>
---
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


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