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

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