[RFC PATCH v3 00/13] virtio/vsock: introduce SOCK_SEQPACKET support

Arseny Krasnov
2021-01-25T11:21:13Z

This patchset impelements support of SOCK_SEQPACKET for virtio
transport.
As SOCK_SEQPACKET guarantees to save record boundaries, so to
do it, new packet operation was added: it marks start of record (with
record length in header), such packet doesn't carry any data. To send
record, packet with start marker is sent first, then all data is sent
as usual 'RW' packets. On receiver's side, length of record is known
from packet with start record marker. Now as packets of one socket
are not reordered neither on vsock nor on vhost transport layers, such
marker 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 (13):
af_vsock: prepare for SOCK_SEQPACKET support
af_vsock: prepare 'vsock_connectible_recvmsg()'
af_vsock: implement SEQPACKET rx loop
af_vsock: implement send logic for SOCK_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

drivers/vhost/vsock.c | 7 +-
include/linux/virtio_vsock.h | 12 +
include/net/af_vsock.h | 6 +
include/uapi/linux/virtio_vsock.h | 9 +
net/vmw_vsock/af_vsock.c | 543 ++++++++++++++++------
net/vmw_vsock/virtio_transport.c | 4 +
net/vmw_vsock/virtio_transport_common.c | 295 ++++++++++--
tools/testing/vsock/util.c | 32 +-
tools/testing/vsock/util.h | 3 +
tools/testing/vsock/vsock_test.c | 126 +++++
10 files changed, 862 insertions(+), 175 deletions(-)

TODO:
- Support for record integrity control. As transport could drop some
packets, something like "record-id" and record end marker need to
be implemented. Idea is that SEQ_BEGIN packet carries both record
length and record id, end marker(let it be SEQ_END) carries only
record id. To be sure that no one packet was lost, receiver checks
length of data between SEQ_BEGIN and SEQ_END(it must be same with
value in SEQ_BEGIN) and record ids of SEQ_BEGIN and SEQ_END(this
means that both markers were not dropped. I think that easiest way
to implement record id for SEQ_BEGIN is to reuse another field of
packet header(SEQ_BEGIN already uses 'flags' as record length).For
SEQ_END record id could be stored in 'flags'.
Another way to implement it, is to move metadata of both SEQ_END
and SEQ_BEGIN to payload. But this approach has problem, because
if we move something to payload, such payload is accounted by
credit logic, which fragments payload, while payload with record
length and id couldn't be fragmented. One way to overcome it is to
ignore credit update for SEQ_BEGIN/SEQ_END packet.Another solution
is to update 'stream_has_space()' function: current implementation
return non-zero when at least 1 byte is allowed to use,but updated
version will have extra argument, which is needed length. For 'RW'
packet this argument is 1, for SEQ_BEGIN it is sizeof(record len +
record id) and for SEQ_END it is sizeof(record id).

- 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).

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.

Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>

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2.25.1