xn ethernet issues as DOMU under NetBSD DOM0

[Wei Liu]

I've only gotten two emails on this, so forgive me if this has been
discussed.

On Sat, May 07, 2016 at 04:11:52PM +0000, Stephen Jones wrote:
> From: kmacybsd at gmail.com [mailto:kmacybsd at gmail.com] On Behalf Of K. Macy
> >That would explain it. If the Linux backend supports TSO, then netfront will of course advertise TSO. And >presumably there's no way to query the netback, since Xen is linux-centric. Assuming you haven't already I would >disable TSO.
> 
> > Or have you already tried that?
> 
> This morning I've tried building a kernel without the TCP_OFFLOAD option.  When booting the new system, I see this in dmesg:
> 
> xn0:  <Virtual Network Interface> at device/vif/0 on xenbusb_front0
> xn0:  Ethernet address:  00:16:3e:00:00:30
> xn0:  backend features:  feature-sg feature-gso-tcp4
> xn_txeof:  WARNING:  response is -1!
> 

This means the backend returns -1 for the tx request, but -1 is just
a general error code so it doesn't reveal much.

It would be interesting to see if there is anything shown on the backend
side -- if netbsd's netback logs something.

> Ifconfig -v xn0 looks like:
> 
> xn0:  flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
> 	options=403<RXCSUM,TXCSUM,LRO>
> 
> Pings work, ftp works (I was able to get the src.txz file off of ftp.freebsd.org to build the kernel)
> ssh does not work (handshaking fails) but I can login via telnet.  However, just about anything
> that requires lots of output gets a bit clobbered.
> 
> Are there any other kernel/sysctl parameters I should be disabling?
> 
> It is almost working, but I need help to know if this is a netfront or a netback issue.  If it is a NetBSD issue
> I'll move the discussion over to port-xen at netbsd.org

I think what you can do is to try the same kernel with a Linux backend.
That would be a good way of telling which side is at fault.

Wei.