Re: [External] Re: vsock virtio: questions about supporting DGRAM type

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Mar 11, 2021 at 08:57:08PM -0800, Jiang Wang . wrote:
> Hi Michael,
> 
> Sorry for the late reply. I just saw your email yesterday somehow.
> 
> I read the email thread you mentioned, and I think the issue with
> dgram is that it may drop packets because the sender cannot track the
> tx_cnt with subtracting it from peer_fwd_cnt.
> 
> I agree with Stefan that the dgram is a best-effort service and may
> drop packets. For the sender, I just add a maximum buffer size to
> limit the memory usage. On the receiving side, I reuse the existing
> virtio_transport_inc_rx_pkt() that Stefano added a year ago to limit
> the memory usage. This will avoid denial of service attack to the
> other end (host or guest VM).
> 
> For the application of dgram, we will use it for some remote logging
> application. The application running in the VM will write some logs to
> a server running on the host. This is  one way communication and the
> log is not critical.
> 
> Regards,
> 
> Jiang

To make things short, please submit to the virtio TC a spec patch
documenting how is dgram supposed to work and we'll discuss.  The
existing mechanism was designed with a stream socket in mind.  dgram is
best-effort but some fairness could be a quality of implementation
issue.  I appreciate that your specific application might not care about
such concerns but we do need to worry about building a widely reuseable
interface as opposed to a very narrow one.

-- 
MST

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