On 12.03.2021 18:20, Stefano Garzarella wrote:

On Sun, Mar 07, 2021 at 09:02:31PM +0300, Arseny Krasnov wrote:

quoted

This adds transport callback which tries to fetch record begin marker
from socket's rx queue. It is called from af_vsock.c before reading data
packets of record.

Signed-off-by: Arseny Krasnov <redacted>
---
include/linux/virtio_vsock.h            |  1 +
net/vmw_vsock/virtio_transport_common.c | 53 +++++++++++++++++++++++++
2 files changed, 54 insertions(+)

diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index 466a5832d2f5..d7edcfeb4cd2 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h

@@ -88,6 +88,7 @@ virtio_transport_dgram_dequeue(struct vsock_sock *vsk,

			       struct msghdr *msg,
			       size_t len, int flags);

+size_t virtio_transport_seqpacket_seq_get_len(struct vsock_sock *vsk);
int
virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
				   struct msghdr *msg,

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 5f1e283e43f3..6fc78fec41c0 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c

@@ -399,6 +399,59 @@ static inline void virtio_transport_remove_pkt(struct virtio_vsock_pkt *pkt)

	virtio_transport_free_pkt(pkt);
}

+static size_t virtio_transport_drop_until_seq_begin(struct virtio_vsock_sock *vvs)
+{
+	struct virtio_vsock_pkt *pkt, *n;
+	size_t bytes_dropped = 0;
+
+	list_for_each_entry_safe(pkt, n, &vvs->rx_queue, list) {
+		if (le16_to_cpu(pkt->hdr.op) == VIRTIO_VSOCK_OP_SEQ_BEGIN)
+			break;
+
+		bytes_dropped += le32_to_cpu(pkt->hdr.len);
+		virtio_transport_dec_rx_pkt(vvs, pkt);
+		virtio_transport_remove_pkt(pkt);
+	}
+
+	return bytes_dropped;
+}
+
+size_t virtio_transport_seqpacket_seq_get_len(struct vsock_sock *vsk)
+{
+	struct virtio_vsock_seq_hdr *seq_hdr;
+	struct virtio_vsock_sock *vvs;
+	struct virtio_vsock_pkt *pkt;
+	size_t bytes_dropped;
+
+	vvs = vsk->trans;
+
+	spin_lock_bh(&vvs->rx_lock);
+
+	/* Fetch all orphaned 'RW' packets and send credit update. */
+	bytes_dropped = virtio_transport_drop_until_seq_begin(vvs);
+
+	if (list_empty(&vvs->rx_queue))
+		goto out;

What do we return to in this case?

IIUC we return the len of the previous packet, should we set 
vvs->seqpacket_state.user_read_seq_len to 0?

Yes, i think that's true

quoted

+
+	pkt = list_first_entry(&vvs->rx_queue, struct virtio_vsock_pkt, list);
+
+	vvs->seqpacket_state.user_read_copied = 0;
+
+	seq_hdr = (struct virtio_vsock_seq_hdr *)pkt->buf;
+	vvs->seqpacket_state.user_read_seq_len = 
le32_to_cpu(seq_hdr->msg_len);
+	vvs->seqpacket_state.curr_rx_msg_id = le32_to_cpu(seq_hdr->msg_id);
+	virtio_transport_dec_rx_pkt(vvs, pkt);
+	virtio_transport_remove_pkt(pkt);
+out:
+	spin_unlock_bh(&vvs->rx_lock);
+
+	if (bytes_dropped)
+		virtio_transport_send_credit_update(vsk);
+
+	return vvs->seqpacket_state.user_read_seq_len;
+}
+EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_seq_get_len);
+
static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
						 struct msghdr *msg,
						 bool *msg_ready)
-- 
2.25.1