Subject: Re: [RFC PATCH v5 11/19] virtio/vsock: dequeue callback for SOCK_SEQPACKET

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 23 Feb 2021 09:17:01 -0500

On Thu, Feb 18, 2021 at 08:39:37AM +0300, 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. If during copy SEQ_BEGIN
> was found(and not all data was copied), copying is restarted by reset
> user's iov iterator(previous unfinished data is dropped).
> 
> Signed-off-by: Arseny Krasnov <[email-masked]>
> ---
>  include/linux/virtio_vsock.h            |  10 +++
>  include/uapi/linux/virtio_vsock.h       |  16 ++++
>  net/vmw_vsock/virtio_transport_common.c | 114 ++++++++++++++++++++++++
>  3 files changed, 140 insertions(+)
> 
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index dc636b727179..003d06ae4a85 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -36,6 +36,11 @@ struct virtio_vsock_sock {
>  	u32 rx_bytes;
>  	u32 buf_alloc;
>  	struct list_head rx_queue;
> +
> +	/* For SOCK_SEQPACKET */
> +	u32 user_read_seq_len;
> +	u32 user_read_copied;
> +	u32 curr_rx_msg_cnt;

wrap these in a struct to make it's clearer they
are related?

>  };
>  
>  struct virtio_vsock_pkt {
> @@ -80,6 +85,11 @@ virtio_transport_dgram_dequeue(struct vsock_sock *vsk,
>  			       struct msghdr *msg,
>  			       size_t len, int flags);
>  
> +int
> +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/include/uapi/linux/virtio_vsock.h b/include/uapi/linux/virtio_vsock.h
> index 1d57ed3d84d2..cf9c165e5cca 100644
> --- a/include/uapi/linux/virtio_vsock.h
> +++ b/include/uapi/linux/virtio_vsock.h
> @@ -63,8 +63,14 @@ struct virtio_vsock_hdr {
>  	__le32	fwd_cnt;
>  } __attribute__((packed));
>  
> +struct virtio_vsock_seq_hdr {
> +	__le32  msg_cnt;
> +	__le32  msg_len;
> +} __attribute__((packed));
> +
>  enum virtio_vsock_type {
>  	VIRTIO_VSOCK_TYPE_STREAM = 1,
> +	VIRTIO_VSOCK_TYPE_SEQPACKET = 2,
>  };
>  
>  enum virtio_vsock_op {
> @@ -83,6 +89,11 @@ enum virtio_vsock_op {
>  	VIRTIO_VSOCK_OP_CREDIT_UPDATE = 6,
>  	/* Request the peer to send the credit info to us */
>  	VIRTIO_VSOCK_OP_CREDIT_REQUEST = 7,
> +
> +	/* Record begin for SOCK_SEQPACKET */
> +	VIRTIO_VSOCK_OP_SEQ_BEGIN = 8,
> +	/* Record end for SOCK_SEQPACKET */
> +	VIRTIO_VSOCK_OP_SEQ_END = 9,
>  };
>  
>  /* VIRTIO_VSOCK_OP_SHUTDOWN flags values */
> @@ -91,4 +102,9 @@ enum virtio_vsock_shutdown {
>  	VIRTIO_VSOCK_SHUTDOWN_SEND = 2,
>  };
>  
> +/* VIRTIO_VSOCK_OP_RW flags values */
> +enum virtio_vsock_rw {
> +	VIRTIO_VSOCK_RW_EOR = 1,
> +};
> +
>  #endif /* _UAPI_LINUX_VIRTIO_VSOCK_H */

Probably a good idea to also have a feature bit gating
this functionality.

-- 
MST