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