Re: [virtio-dev] [RFC] vsock: add vsock device

[Stefan Hajnoczi <stefanha@redhat.com>]

On Wed, Jun 03, 2015 at 10:56:52AM +0100, Stefan Hajnoczi wrote:
> On Tue, Jun 02, 2015 at 04:29:06PM +0200, Michael S. Tsirkin wrote:
> > On Tue, Jun 02, 2015 at 03:17:39PM +0100, Stefan Hajnoczi wrote:
> > > On Mon, Jun 01, 2015 at 05:39:15PM +0200, Michael S. Tsirkin wrote:
> > > > On Thu, May 21, 2015 at 05:40:41PM +0100, Stefan Hajnoczi wrote:
> > > Perhaps we should drop the buffer space mechanism for dgram flows and
> > > make the counters per-flow for streams.  That way the denial-of-service
> > > issue is avoided.  Does that sound good?
> > 
> > As I mentioned separately, I'm not sure what does buffer space mechanism
> > mean for dgram flows, since a flow must track msg boundaries which
> > has memory overhead (for stream flows, small messages can be packed
> > into a single buffer if necessary).
> 
> The receiver has a finite buffer size.  If the receiving userspace
> application doesn't read from the buffer fast enough it can become full.
> I guess the idea of buffer space management for dgram was to avoid
> dropping packets by letting the sender know they must wait.

Hmm...the problem is that a dgram sender cannot track tx_cnt and
subtract peer_fwd_cnt since peer_fwd_cnt includes the number of bytes
received from all senders to this dgram socket.

If we drop buffer space management for dgram flows then it's equivalent
to UDP.  That should be fine.

Stefan

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