Re: [RFC PATCH v8 11/19] virtio/vsock: dequeue callback for SOCK_SEQPACKET

[Arseny Krasnov <arseny.krasnov@kaspersky.com>]

I'll fix some issues of this patch found by kernel test robot

On 13.04.2021 15:44, Arseny Krasnov wrote:
> This adds transport callback and it's logic for SEQPACKET dequeue.
> Callback fetches RW packets from rx queue of socket until whole record
> is copied(if user's buffer is full, user is not woken up). This is done
> to not stall sender, because if we wake up user and it leaves syscall,
> nobody will send credit update for rest of record, and sender will wait
> for next enter of read syscall at receiver's side. So if user buffer is
> full, we just send credit update and drop data.
>
> Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
> ---
> v7 -> v8:
>  - Things like SEQ_BEGIN, SEQ_END, 'msg_len' and 'msg_id' now removed.
>    This callback fetches and copies RW packets to user's buffer, until
>    last packet of message found(this packet is marked in 'flags' field
>    of header).
>
>  include/linux/virtio_vsock.h            |  5 ++
>  net/vmw_vsock/virtio_transport_common.c | 73 +++++++++++++++++++++++++
>  2 files changed, 78 insertions(+)
>
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index dc636b727179..02acf6e9ae04 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -80,6 +80,11 @@ virtio_transport_dgram_dequeue(struct vsock_sock *vsk,
>  			       struct msghdr *msg,
>  			       size_t len, int flags);
>  
> +ssize_t
> +virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
> +				   struct msghdr *msg,
> +				   int flags,
> +				   bool *msg_ready);
>  s64 virtio_transport_stream_has_data(struct vsock_sock *vsk);
>  s64 virtio_transport_stream_has_space(struct vsock_sock *vsk);
>  
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index 833104b71a1c..8492b8bd5df5 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -393,6 +393,67 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
>  	return err;
>  }
>  
> +static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
> +						 struct msghdr *msg,
> +						 int flags,
> +						 bool *msg_ready)
> +{
> +	struct virtio_vsock_sock *vvs = vsk->trans;
> +	struct virtio_vsock_pkt *pkt;
> +	int err = 0;
> +	size_t user_buf_len = msg->msg_iter.count;
> +
> +	*msg_ready = false;
> +	spin_lock_bh(&vvs->rx_lock);
> +
> +	while (!*msg_ready && !list_empty(&vvs->rx_queue) && err >= 0) {
> +		pkt = list_first_entry(&vvs->rx_queue, struct virtio_vsock_pkt, list);
> +
> +		if (le16_to_cpu(pkt->hdr.op) == VIRTIO_VSOCK_OP_RW) {
> +			size_t bytes_to_copy;
> +			size_t pkt_len;
> +
> +			pkt_len = (size_t)le32_to_cpu(pkt->hdr.len);
> +			bytes_to_copy = min(user_buf_len, pkt_len);
> +
> +			/* sk_lock is held by caller so no one else can dequeue.
> +			 * Unlock rx_lock since memcpy_to_msg() may sleep.
> +			 */
> +			spin_unlock_bh(&vvs->rx_lock);
> +
> +			if (memcpy_to_msg(msg, pkt->buf, bytes_to_copy)) {
> +				err = -EINVAL;
> +				break;
> +			}
> +
> +			spin_lock_bh(&vvs->rx_lock);
> +
> +			/* If user sets 'MSG_TRUNC' we return real length
> +			 * of message.
> +			 */
> +			if (flags & MSG_TRUNC)
> +				err += pkt_len;
> +			else
> +				err += bytes_to_copy;
> +
> +			user_buf_len -= bytes_to_copy;
> +
> +			if (pkt->hdr.flags & VIRTIO_VSOCK_SEQ_EOR)
> +				*msg_ready = true;
> +		}
> +
> +		virtio_transport_dec_rx_pkt(vvs, pkt);
> +		list_del(&pkt->list);
> +		virtio_transport_free_pkt(pkt);
> +	}
> +
> +	spin_unlock_bh(&vvs->rx_lock);
> +
> +	virtio_transport_send_credit_update(vsk);
> +
> +	return err;
> +}
> +
>  ssize_t
>  virtio_transport_stream_dequeue(struct vsock_sock *vsk,
>  				struct msghdr *msg,
> @@ -405,6 +466,18 @@ virtio_transport_stream_dequeue(struct vsock_sock *vsk,
>  }
>  EXPORT_SYMBOL_GPL(virtio_transport_stream_dequeue);
>  
> +ssize_t
> +virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
> +				   struct msghdr *msg,
> +				   int flags, bool *msg_ready)
> +{
> +	if (flags & MSG_PEEK)
> +		return -EOPNOTSUPP;
> +
> +	return virtio_transport_seqpacket_do_dequeue(vsk, msg, flags, msg_ready);
> +}
> +EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_dequeue);
> +
>  int
>  virtio_transport_dgram_dequeue(struct vsock_sock *vsk,
>  			       struct msghdr *msg,