Re: [RFC PATCH v4 00/17] virtio/vsock: introduce SOCK_SEQPACKET support

[Arseny Krasnov]

On 11.02.2021 17:57, Stefano Garzarella wrote:
> Hi Arseny,
>
> On Mon, Feb 08, 2021 at 09:32:59AM +0300, Arseny Krasnov wrote:
>> On 07.02.2021 19:20, Michael S. Tsirkin wrote:
>>> On Sun, Feb 07, 2021 at 06:12:56PM +0300, Arseny Krasnov wrote:
>>>> 	This patchset impelements 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 count and message length:
>>>>
>>>> 	struct virtio_vsock_seq_hdr {
>>>> 		__le32  msg_cnt;
>>>> 		__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 contains length of record and counter), then
>>>> counter is incremented and all data is sent as usual 'RW' packets and
>>>> finally SEQ_END is sent(it also carries counter of message, which is
>>>> counter of SEQ_BEGIN + 1), also after sedning SEQ_END counter is
>>>> incremented again. On receiver's side, length of record is known from
>>>> packet with start record marker. To check that no packets were dropped
>>>> by transport, counters of two sequential SEQ_BEGIN and SEQ_END are
>>>> checked(counter of SEQ_END must be bigger that counter of SEQ_BEGIN by
>>>> 1) and length of data between two markers is compared to 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.
>>>>
>>>>  Arseny Krasnov (17):
>>>>   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: 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: setup SEQPACKET ops for transport
>>>>   vhost/vsock: setup SEQPACKET ops for transport
>>>>   vsock_test: add SOCK_SEQPACKET tests
>>>>   loopback/vsock: setup SEQPACKET ops for transport
>>>>   virtio/vsock: simplify credit update function API
>>>>
>>>>  drivers/vhost/vsock.c                   |   8 +-
>>>>  include/linux/virtio_vsock.h            |  15 +
>>>>  include/net/af_vsock.h                  |   9 +
>>>>  include/uapi/linux/virtio_vsock.h       |  16 +
>>>>  net/vmw_vsock/af_vsock.c                | 588 +++++++++++++++-------
>>>>  net/vmw_vsock/virtio_transport.c        |   5 +
>>>>  net/vmw_vsock/virtio_transport_common.c | 316 ++++++++++--
>>>>  net/vmw_vsock/vsock_loopback.c          |   5 +
>>>>  tools/testing/vsock/util.c              |  32 +-
>>>>  tools/testing/vsock/util.h              |   3 +
>>>>  tools/testing/vsock/vsock_test.c        | 126 +++++
>>>>  11 files changed, 895 insertions(+), 228 deletions(-)
>>>>
>>>>  TODO:
>>>>  - What to do, when server doesn't support SOCK_SEQPACKET. In current
>>>>    implementation RST is replied in the same way when listening port
>>>>    is not found. I think that current RST is enough,because case when
>>>>    server doesn't support SEQ_PACKET is same when listener missed(e.g.
>>>>    no listener in both cases).
> I think is fine.
>
>>>    - virtio spec patch
>> Ok
> Yes, please prepare a patch to discuss the VIRTIO spec changes.
>
> For example for 'virtio_vsock_seq_hdr', I left a comment about 'msg_cnt' 
> naming that should be better to discuss with virtio guys.

Ok, i'll prepare it in v5. So I have to send it both LKML(as one of patches) and

virtio mailing lists? (e.g. virtio-comment@xxxxxxxxxxxxxxxxxxxx)

>
> Anyway, I reviewed this series and I left some comments.
> I think we are in a good shape :-)
Great, thanks for review. I'll consider all review comments in next version.
>
> Thanks,
> Stefano
>
>