Re: [Qemu-devel] Question about VM inner route entry's lost when vhost-user reconnect

[Stefan Hajnoczi]

On Tue, Mar 12, 2019 at 02:01:04AM +0000, Lilijun (Jerry, Cloud Networking) 
wrote:
> 
> 
> > -----Original Message-----
> > From: Stefan Hajnoczi [mailto:address@hidden
> > Sent: Monday, March 11, 2019 5:47 PM
> > To: Lilijun (Jerry, Cloud Networking) <address@hidden>
> > Cc: address@hidden; wangxin (U)
> > <address@hidden>; wangyunjian
> > <address@hidden>
> > Subject: Re: [Qemu-devel] Question about VM inner route entry's lost when
> > vhost-user reconnect
> > 
> > On Fri, Mar 08, 2019 at 02:31:12AM +0000, Lilijun (Jerry, Cloud Networking)
> > wrote:
> > > This problem is related with backend vhost-user socket abnormal cases, we
> > shouldn't ask customers to configure it manually for backend's issues or
> > depends on guest OS's network configuration.
> > 
> > In Step 1 you said:
> > 
> > > > >      1) In the VM, I add one route entry manually on the vNIC eth0
> > > > > using the
> > > > linux tool route.
> > 
> > You configured the route manually inside the guest.  Seems like a guest
> > problem to me.
> > 
> > If this was a physical machine that lost connectivity due to a link event, 
> > what
> > would happen?
> 
> Yes, the configuration can be recovered manually by customers.
> 
> But in the virtualization machines, this configuration's lost is a result of 
> backend process's software unexpected bugs or version update. So I think we 
> need hide this change to customers.

My question is:

Do manually added routes disappear on a physical machine when the link
goes down?

If yes, then the VM is acting correctly and this issue can be solved by
configuring the guest appropriately.  (Hiding the link down event might
seem nice in this particular situation but other users might need the
event.  Usually it's best to follow how physical machines behave and
rely on existing solutions instead of implementing different behavior
for VMs because that leads to new problems that are hard to foresee.)

If no, then why is the guest treating the virtio-net link down
differently?  Could be a bug.

Stefan

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