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

[Arseny Krasnov]

On 25.03.2021 13:52, Stefano Garzarella wrote:
> 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.
I'll prepare new version of specification patch
>
> What do you think?
Agree, Thank You
>
> Thanks,
> Stefano
>
>