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

[Jason Wang <jasowang@redhat.com>]

在 2021/6/10 上午11:43, Jiang Wang . 写道:
> On Wed, Jun 9, 2021 at 6:51 PM Jason Wang <jasowang@redhat.com> 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@huawei.com/
[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(-)
>>>