Re: [RFC v1 0/6] virtio/vsock: introduce SOCK_DGRAM support

[Jason Wang]

在 2021/6/10 上午11:43, Jiang Wang . 写道:
> On Wed, Jun 9, 2021 at 6:51 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > 在 2021/6/10 上午7:24, Jiang Wang 写道:
> > > This patchset implements support of SOCK_DGRAM for virtio
> > > transport.
> > >
> > > Datagram sockets are connectionless and unreliable. To avoid unfair contention
> > > with stream and other sockets, add two more virtqueues and
> > > a new feature bit to indicate if those two new queues exist or not.
> > >
> > > Dgram does not use the existing credit update mechanism for
> > > stream sockets. When sending from the guest/driver, sending packets
> > > synchronously, so the sender will get an error when the virtqueue is full.
> > > When sending from the host/device, send packets asynchronously
> > > because the descriptor memory belongs to the corresponding QEMU
> > > process.
> >
> > What's the use case for the datagram vsock?
> One use case is for non critical info logging from the guest
> to the host, such as the performance data of some applications.


Anything that prevents you from using the stream socket?


> It can also be used to replace UDP communications between
> the guest and the host.


Any advantage for VSOCK in this case? Is it for performance (I guess not 
since I don't exepct vsock will be faster).

An obvious drawback is that it breaks the migration. Using UDP you can 
have a very rich features support from the kernel where vsock can't.


> > > The virtio spec patch is here:
> > > https://www.spinics.net/lists/linux-virtualization/msg50027.html
> >
> > Have a quick glance, I suggest to split mergeable rx buffer into an
> > separate patch.
> Sure.
>
> > But I think it's time to revisit the idea of unifying the virtio-net and
> > virtio-vsock. Otherwise we're duplicating features and bugs.
> For mergeable rxbuf related code, I think a set of common helper
> functions can be used by both virtio-net and virtio-vsock. For other
> parts, that may not be very beneficial. I will think about more.
>
> If there is a previous email discussion about this topic, could you send me
> some links? I did a quick web search but did not find any related
> info. Thanks.


We had a lot:

[1] 
https://patchwork.kernel.org/project/kvm/patch/5BDFF537.3050806@xxxxxxxxxx/
[2] 
https://lists.linuxfoundation.org/pipermail/virtualization/2018-November/039798.html
[3] https://www.lkml.org/lkml/2020/1/16/2043

Thanks

> > Thanks
> >
> >
> > > For those who prefer git repo, here is the link for the linux kernel：
> > > https://github.com/Jiang1155/linux/tree/vsock-dgram-v1
> > >
> > > qemu patch link:
> > > https://github.com/Jiang1155/qemu/tree/vsock-dgram-v1
> > >
> > >
> > > To do:
> > > 1. use skb when receiving packets
> > > 2. support multiple transport
> > > 3. support mergeable rx buffer
> > >
> > >
> > > Jiang Wang (6):
> > >     virtio/vsock: add VIRTIO_VSOCK_F_DGRAM feature bit
> > >     virtio/vsock: add support for virtio datagram
> > >     vhost/vsock: add support for vhost dgram.
> > >     vsock_test: add tests for vsock dgram
> > >     vhost/vsock: add kconfig for vhost dgram support
> > >     virtio/vsock: add sysfs for rx buf len for dgram
> > >
> > >    drivers/vhost/Kconfig                              |   8 +
> > >    drivers/vhost/vsock.c                              | 207 ++++++++--
> > >    include/linux/virtio_vsock.h                       |   9 +
> > >    include/net/af_vsock.h                             |   1 +
> > >    .../trace/events/vsock_virtio_transport_common.h   |   5 +-
> > >    include/uapi/linux/virtio_vsock.h                  |   4 +
> > >    net/vmw_vsock/af_vsock.c                           |  12 +
> > >    net/vmw_vsock/virtio_transport.c                   | 433 ++++++++++++++++++---
> > >    net/vmw_vsock/virtio_transport_common.c            | 184 ++++++++-
> > >    tools/testing/vsock/util.c                         | 105 +++++
> > >    tools/testing/vsock/util.h                         |   4 +
> > >    tools/testing/vsock/vsock_test.c                   | 195 ++++++++++
> > >    12 files changed, 1070 insertions(+), 97 deletions(-)