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

[Stefano Garzarella <sgarzare@redhat.com>]

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.

Anyway, I reviewed this series and I left some comments.
I think we are in a good shape :-)

Thanks,
Stefano