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Date:   Mon, 8 Feb 2021 09:32:59 +0300
From:   Arseny Krasnov <arseny.krasnov@...persky.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jorgen Hansen <jhansen@...are.com>,
        Andra Paraschiv <andraprs@...zon.com>,
        Colin Ian King <colin.king@...onical.com>,
        Alexander Popov <alex.popov@...ux.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stsp2@...dex.ru" <stsp2@...dex.ru>,
        "oxffffaa@...il.com" <oxffffaa@...il.com>
Subject: Re: [RFC PATCH v4 00/17] virtio/vsock: introduce SOCK_SEQPACKET
 support


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).
>    - virtio spec patch
Ok
>
>>  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
>

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