Re: [Xen-devel] reboot driver domain, vifX.Y = NO-CARRIER?

[Jason Cooper <xen@xxxxxxxxxxxxxx>]

Hi Wei Liu,

On Tue, May 01, 2018 at 12:50:13PM +0100, Wei Liu wrote:
> On Mon, Apr 30, 2018 at 04:16:09PM +0000, Jason Cooper wrote:
> > On Mon, Apr 30, 2018 at 04:22:30PM +0100, Ian Jackson wrote:
...
> > > I think the right answer is that this is simply a bug in the
> > > frontends.  frontends should cope if the backend path pointer in the
> > > frontend directory is updated, and should start reading the new
> > > backend instead.
> > 
> > Ok, so I'm new to the guts of Xen.  The bug, at a high level, is that
> > "When a driver domain is rebooted (domid changed), previously connected
> > client domUs can't gain network connectivity to/through the driver
> > domain via 'xl network-attach client_domu mac=... bridge=...
> > backend=drv_dom'"
> 
> This seems to be different from what I originally understood. I thought
> you were just expecting the frontend to reconnect automatically.

When I call 'xl network-attach ... backend=drv_dom', yes.

> At the risk of asking the obvious question: drv_dom is the name not
> numeric domid, right?

Correct.

> > This is due to the fact that the frontend net driver doesn't / can't
> > follow the backend driver to the new domid in xenstore.
> > 
> 
> This is strange. A new udev event should be initiated in DomU. It will
> then scans xenstore for a _new_ network device. There should be a new
> device from DomU's PoV, which means it doesn't need to know what backend
> domid is. This should be already handled by core xenbus driver.

So, when I do 'xl network-detach ...; xl reboot drv_dom; xl
network-attach ...', that should be the equivalent of pulling out the
network card for the DomU?  I was envisioning it to be more akin to
unplugging the network cable and then plugging it back in.

My rootfs is >90% busybox atm, so I'm using mdev.  To my knowledge, I've
setup the mdev hotplug scripts correctly and set mdev as the binary for
the kernel to call on hotplug events.  So it *should* be removing and
adding the device if called.

ftr, the full DomUs, Gentoo and Debian both exhibit this problem as
clients to drv_dom, and I've not messed with their network / hotplug
setups.  Other than standard network configuration.

thx,

Jason.

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