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

[Michael S. Tsirkin]

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).

   - virtio spec patch

>  v3 -> v4:
>  - callbacks for loopback transport
>  - SEQPACKET specific metadata moved from packet header to payload
>    and called 'virtio_vsock_seq_hdr'
>  - record integrity check:
>    1) SEQ_END operation was added, which marks end of record.
>    2) Both SEQ_BEGIN and SEQ_END carries counter which is incremented
>       on every marker send.
>  - af_vsock.c: socket operations for STREAM and SEQPACKET call same
>    functions instead of having own "gates" differs only by names:
>    'vsock_seqpacket/stream_getsockopt()' now replaced with
>    'vsock_connectible_getsockopt()'.
>  - af_vsock.c: 'seqpacket_dequeue' callback returns error and flag that
>    record ready. There is no need to return number of copied bytes,
>    because case when record received successfully is checked at virtio
>    transport layer, when SEQ_END is processed. Also user doesn't need
>    number of copied bytes, because 'recv()' from SEQPACKET could return
>    error, length of users's buffer or length of whole record(both are
>    known in af_vsock.c).
>  - af_vsock.c: both wait loops in af_vsock.c(for data and space) moved
>    to separate functions because now both called from several places.
>  - af_vsock.c: 'vsock_assign_transport()' checks that 'new_transport'
>    pointer is not NULL and returns 'ESOCKTNOSUPPORT' instead of 'ENODEV'
>    if failed to use transport.
>  - tools/testing/vsock/vsock_test.c: rename tests
> 
>  v2 -> v3:
>  - patches reorganized: split for prepare and implementation patches
>  - local variables are declared in "Reverse Christmas tree" manner
>  - virtio_transport_common.c: valid leXX_to_cpu() for vsock header
>    fields access
>  - af_vsock.c: 'vsock_connectible_*sockopt()' added as shared code
>    between stream and seqpacket sockets.
>  - af_vsock.c: loops in '__vsock_*_recvmsg()' refactored.
>  - af_vsock.c: 'vsock_wait_data()' refactored.
> 
>  v1 -> v2:
>  - patches reordered: af_vsock.c related changes now before virtio vsock
>  - patches reorganized: more small patches, where +/- are not mixed
>  - tests for SOCK_SEQPACKET added
>  - all commit messages updated
>  - af_vsock.c: 'vsock_pre_recv_check()' inlined to
>    'vsock_connectible_recvmsg()'
>  - af_vsock.c: 'vsock_assign_transport()' returns ENODEV if transport
>    was not found
>  - virtio_transport_common.c: transport callback for seqpacket dequeue
>  - virtio_transport_common.c: simplified
>    'virtio_transport_recv_connected()'
>  - virtio_transport_common.c: send reset on socket and packet type
> 			      mismatch.
> 
> -- 
> 2.25.1