netdev - Re: AF_VSOCK loopback

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Date:   Thu, 10 Nov 2016 11:17:55 -0500
From:   Cathy Avery <cavery@...hat.com>
To:     Stefan Hajnoczi <stefanha@...hat.com>,
        Jorgen Hansen <jhansen@...are.com>
Cc:     netdev@...r.kernel.org
Subject: Re: AF_VSOCK loopback

I had trouble with loopback on the esx host. Using the nc-vsock ( 
AF_VSOCK 56 ) the server and the client connected but they both 
terminated without error when I attempted to send characters over. It 
might be due to something other than vsock. I haven't pursued it yet.

On 11/10/2016 09:43 AM, Stefan Hajnoczi wrote:
> Hi Jorgen,
> Cathy Avery found that the AF_VSOCK VMCI transport does loopback inside
> the guest (but not on the host?).  The virtio transport currently does
> no loopback.
>
> The loopback scenario I'm thinking of is where process A listens on port
> 1234 and process B on the same machine connects to port 1234 both with
> the same CID.
>
> I'd like to make the virtio transport compatible with VMCI transport
> semantics so AF_VSOCK behaves the same regardless of the transport.
> This means loopback must be added to virtio-vsock.
>
> The core net/vmware/af_vsock.c code does not implement loopback.  How
> does VMCI do loopback?  Are the loopback packets reflected back from the
> host?  Or does the guest driver notice the loopback and avoid passing
> packets to the host in the first place?
>
> Maybe we can make the loopback code common in af_vsock.c if that avoids
> code duplication.
>
> Thanks,
> Stefan