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

Stefano Garzarella
2021-03-25T10:53:14Z

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@yandex.ru 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