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

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