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

Stefano Garzarella
2021-03-25T10:08:24Z

On Tue, Mar 23, 2021 at 04:12:55PM +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@kaspersky.com>
>---
> 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;
>+

Okay, I see now, I think you can move this patch before the previous one
or merge them in a single patch, it is better to review and to bisect.

As mentioned, I think we can return msg_len if
virtio_transport_seqpacket_do_dequeue() does not fail, otherwise the
error.

I mean something like this:

static ssize_t virtio_transport_seqpacket_do_dequeue(...)
{
size_t msg_len;
ssize_t ret;

msg_len = virtio_transport_seqpacket_seq_get_len(vsk);
if (msg_len == 0)
return -EAGAIN;

ret = virtio_transport_seqpacket_do_dequeue(vsk, msg, msg_ready);
if (ret < 0)
return ret;

return msg_len;
}

> return virtio_transport_seqpacket_do_dequeue(vsk, msg, msg_ready);
> }
> EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_dequeue);
>-- 2.25.1