linux-kernel - Re: [RFC PATCH v6 12/22] virtio/vsock: fetch length for SEQPACKET record

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Date:   Fri, 12 Mar 2021 16:20:49 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseny Krasnov <arseny.krasnov@...persky.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jorgen Hansen <jhansen@...are.com>,
        Andra Paraschiv <andraprs@...zon.com>,
        Norbert Slusarek <nslusarek@....net>,
        Colin Ian King <colin.king@...onical.com>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        stsp2@...dex.ru, oxffffaa@...il.com
Subject: Re: [RFC PATCH v6 12/22] virtio/vsock: fetch length for SEQPACKET
 record

On Sun, Mar 07, 2021 at 09:02:31PM +0300, Arseny Krasnov wrote:
>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@...persky.com>
>---
> 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?

>+
>+	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
>