Re: [RFC PATCH v3 0/6] virtio/vsock: introduce MSG_EOR flag for SEQPACKET

[Arseny Krasnov <arseny.krasnov@kaspersky.com>]

Hello, please ping :)


On 16.08.2021 11:50, Arseny Krasnov wrote:
> 	This patchset implements support of MSG_EOR bit for SEQPACKET
> AF_VSOCK sockets over virtio transport.
> 	First we need to define 'messages' and 'records' like this:
> Message is result of sending calls: 'write()', 'send()', 'sendmsg()'
> etc. It has fixed maximum length, and it bounds are visible using
> return from receive calls: 'read()', 'recv()', 'recvmsg()' etc.
> Current implementation based on message definition above.
> 	Record has unlimited length, it consists of multiple message,
> and bounds of record are visible via MSG_EOR flag returned from
> 'recvmsg()' call. Sender passes MSG_EOR to sending system call and
> receiver will see MSG_EOR when corresponding message will be processed.
> 	Idea of patchset comes from POSIX: it says that SEQPACKET
> supports record boundaries which are visible for receiver using
> MSG_EOR bit. So, it looks like MSG_EOR is enough thing for SEQPACKET
> and we don't need to maintain boundaries of corresponding send -
> receive system calls. But, for 'sendXXX()' and 'recXXX()' POSIX says,
> that all these calls operates with messages, e.g. 'sendXXX()' sends
> message, while 'recXXX()' reads messages and for SEQPACKET, 'recXXX()'
> must read one entire message from socket, dropping all out of size
> bytes. Thus, both message boundaries and MSG_EOR bit must be supported
> to follow POSIX rules.
> 	To support MSG_EOR new bit was added along with existing
> 'VIRTIO_VSOCK_SEQ_EOR': 'VIRTIO_VSOCK_SEQ_EOM'(end-of-message) - now it
> works in the same way as 'VIRTIO_VSOCK_SEQ_EOR'. But 'VIRTIO_VSOCK_SEQ_EOR'
> is used to mark 'MSG_EOR' bit passed from userspace.
> 	This patchset includes simple test for MSG_EOR.
>
>  Arseny Krasnov(6):
>   virtio/vsock: rename 'EOR' to 'EOM' bit.
>   virtio/vsock: add 'VIRTIO_VSOCK_SEQ_EOR' bit.
>   vhost/vsock: support MSG_EOR bit processing
>   virtio/vsock: support MSG_EOR bit processing
>   af_vsock: rename variables in receive loop
>   vsock_test: update message bounds test for MSG_EOR
>
>  drivers/vhost/vsock.c                   | 22 +++++++++++++---------
>  include/uapi/linux/virtio_vsock.h       |  3 ++-
>  net/vmw_vsock/af_vsock.c                | 10 +++++-----
>  net/vmw_vsock/virtio_transport_common.c | 23 +++++++++++++++--------
>  tools/testing/vsock/vsock_test.c        |  8 +++++++-
>  5 files changed, 42 insertions(+), 24 deletions(-)
>
>  v2 -> v3:
>  - 'virtio/vsock: rename 'EOR' to 'EOM' bit.' - commit message updated.
>  - 'VIRTIO_VSOCK_SEQ_EOR' bit add moved to separate patch.
>  - 'vhost/vsock: support MSG_EOR bit processing' - commit message
>    updated.
>  - 'vhost/vsock: support MSG_EOR bit processing' - removed unneeded
>    'le32_to_cpu()', because input argument was already in CPU
>    endianness.
>
>  v1 -> v2:
>  - 'VIRTIO_VSOCK_SEQ_EOR' is renamed to 'VIRTIO_VSOCK_SEQ_EOM', to
>    support backward compatibility.
>  - use bitmask of flags to restore in vhost.c, instead of separated
>    bool variable for each flag.
>  - test for EAGAIN removed, as logically it is not part of this
>    patchset(will be sent separately).
>  - cover letter updated(added part with POSIX description).
>
> Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
>