[RFC PATCH v7 12/22] virtio/vsock: fetch length for SEQPACKET record

[Arseny Krasnov]

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 <arseny.krasnov@xxxxxxxxxxxxx>
---
 v6 -> v7:
 1) Now 'virtio_transport_seqpacket_seq_get_len()' returns 0, if rx
    queue of socket is empty. Else it returns length of current message
    to handle.
 2) If dequeue callback is called, but there is no detected length of
    message to dequeue, EAGAIN is returned, and outer loop restarts
    receiving.

 net/vmw_vsock/virtio_transport_common.c | 61 +++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index a8f4326e45e8..41f05034593e 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -399,6 +399,62 @@ 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;
+}
+
+static 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 = 0;
+
+	vvs = vsk->trans;
+
+	spin_lock_bh(&vvs->rx_lock);
+
+	/* Have some record to process, return it's length. */
+	if (vvs->seq_state.user_read_seq_len)
+		goto out;
+
+	/* 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;
+
+	pkt = list_first_entry(&vvs->rx_queue, struct virtio_vsock_pkt, list);
+
+	vvs->seq_state.user_read_copied = 0;
+
+	seq_hdr = (struct virtio_vsock_seq_hdr *)pkt->buf;
+	vvs->seq_state.user_read_seq_len = le32_to_cpu(seq_hdr->msg_len);
+	vvs->seq_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->seq_state.user_read_seq_len;
+}
+
 static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
 						 struct msghdr *msg,
 						 bool *msg_ready)
@@ -522,6 +578,11 @@ virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
 	if (flags & MSG_PEEK)
 		return -EOPNOTSUPP;
 
+	*msg_len = virtio_transport_seqpacket_seq_get_len(vsk);
+
+	if (*msg_len == 0)
+		return -EAGAIN;
+
 	return virtio_transport_seqpacket_do_dequeue(vsk, msg, msg_ready);
 }
 EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_dequeue);
-- 
2.25.1