Re: [RFC PATCH v7 00/22] virtio/vsock: introduce SOCK_SEQPACKET support

[Stefano Garzarella]

Hi Arseny,

On Tue, Mar 23, 2021 at 04:07:13PM +0300, Arseny Krasnov wrote:
> 	This patchset implements support of SOCK_SEQPACKET for virtio
> transport.
> 	As SOCK_SEQPACKET guarantees to save record boundaries, so to
> do it, two new packet operations were added: first for start of record
> and second to mark end of record(SEQ_BEGIN and SEQ_END later). Also,
> both operations carries metadata - to maintain boundaries and payload
> integrity. Metadata is introduced by adding special header with two
> fields - message id and message length:
>
> 	struct virtio_vsock_seq_hdr {
> 		__le32  msg_id;
> 		__le32  msg_len;
> 	} __attribute__((packed));
>
> 	This header is transmitted as payload of SEQ_BEGIN and SEQ_END
> packets(buffer of second virtio descriptor in chain) in the same way as
> data transmitted in RW packets. Payload was chosen as buffer for this
> header to avoid touching first virtio buffer which carries header of
> packet, because someone could check that size of this buffer is equal
> to size of packet header. To send record, packet with start marker is
> sent first(it's header carries length of record and id),then all data
> is sent as usual 'RW' packets and finally SEQ_END is sent(it carries
> id of message, which is equal to id of SEQ_BEGIN), also after sending
> SEQ_END id is incremented. On receiver's side,size of record is known
> from packet with start record marker. To check that no packets were
> dropped by transport, 'msg_id's of two sequential SEQ_BEGIN and SEQ_END
> are checked to be equal and length of data between two markers is
> compared to then length in SEQ_BEGIN header.
> 	Now as  packets of one socket are not reordered neither on
> vsock nor on vhost transport layers, such markers allows to restore
> original record on receiver's side. If user's buffer is smaller that
> record length, when all out of size data is dropped.
> 	Maximum length of datagram is not limited as in stream socket,
> because same credit logic is used. Difference with stream socket is
> that user is not woken up until whole record is received or error
> occurred. Implementation also supports 'MSG_EOR' and 'MSG_TRUNC' flags.
> 	Tests also implemented.
>
> 	Thanks to stsp2@xxxxxxxxx for encouragements and initial design
> recommendations.
>
> Arseny Krasnov (22):
>  af_vsock: update functions for connectible socket
>  af_vsock: separate wait data loop
>  af_vsock: separate receive data loop
>  af_vsock: implement SEQPACKET receive loop
>  af_vsock: separate wait space loop
>  af_vsock: implement send logic for SEQPACKET
>  af_vsock: rest of SEQPACKET support
>  af_vsock: update comments for stream sockets
>  virtio/vsock: set packet's type in virtio_transport_send_pkt_info()
>  virtio/vsock: simplify credit update function API
>  virtio/vsock: dequeue callback for SOCK_SEQPACKET
>  virtio/vsock: fetch length for SEQPACKET record
>  virtio/vsock: add SEQPACKET receive logic
>  virtio/vsock: rest of SOCK_SEQPACKET support
>  virtio/vsock: SEQPACKET support feature bit
>  virtio/vsock: setup SEQPACKET ops for transport
>  vhost/vsock: setup SEQPACKET ops for transport
>  vsock/loopback: setup SEQPACKET ops for transport
>  vhost/vsock: SEQPACKET feature bit support
>  virtio/vsock: SEQPACKET feature bit support
>  vsock_test: add SOCK_SEQPACKET tests
>  virtio/vsock: update trace event for SEQPACKET
>
> drivers/vhost/vsock.c                        |  21 +-
> include/linux/virtio_vsock.h                 |  21 +
> include/net/af_vsock.h                       |   9 +
> .../events/vsock_virtio_transport_common.h   |  48 +-
> include/uapi/linux/virtio_vsock.h            |  19 +
> net/vmw_vsock/af_vsock.c                     | 581 +++++++++++------
> net/vmw_vsock/virtio_transport.c             |  17 +
> net/vmw_vsock/virtio_transport_common.c      | 379 +++++++++--
> net/vmw_vsock/vsock_loopback.c               |  12 +
> tools/testing/vsock/util.c                   |  32 +-
> tools/testing/vsock/util.h                   |   3 +
> tools/testing/vsock/vsock_test.c             | 126 ++++
> 12 files changed, 1015 insertions(+), 253 deletions(-)
>
> v6 -> v7:
> General changelog:
> - virtio transport callback for message length now removed
>   from transport. Length of record is returned by dequeue
>   callback.
>
> - function which tries to get message length now returns 0
>   when rx queue is empty. Also length of current message in
>   progress is set to 0, when message processed or error
>   happens.
>
> - patches for virtio feature bit moved after patches with
>   transport ops.
>
> Per patch changelog:
>  see every patch after '---' line.

I reviewed the series and I left some comments, I think we are at a good 
point, but we should have the specification accepted before merging this 
series to avoid having to change the implementation later.

What do you think?

Thanks,
Stefano