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

[George Dunlap <dunlapg@xxxxxxxxx>]

On Mon, Apr 30, 2018 at 7:17 PM, Jason Cooper <xen@xxxxxxxxxxxxxx> wrote:
> Hi George,
>
> On Mon, Apr 30, 2018 at 05:38:55PM +0100, George Dunlap wrote:
>> On Mon, Apr 30, 2018 at 5:16 PM, Jason Cooper <xen@xxxxxxxxxxxxxx> wrote:
>> > Hi Ian,
>> >
>> > On Mon, Apr 30, 2018 at 04:22:30PM +0100, Ian Jackson wrote:
>> >> Wei Liu writes ("Re: [Xen-devel] reboot driver domain, vifX.Y = 
>> >> NO-CARRIER?"):
>> >> > To implement reuse_domid in a sane way, either the toolstack needs to
>> >> > manage all domids and always sets domid when creating domain or the
>> >> > hypervisor needs to cooperate -- to have interface to reserve /
>> >> > pre-allocate domids.
>> >>
>> >> I think this is entirely the wrong approach.
>> >
>> > Whew.  Glad I didn't start hacking yet...
>> >
>> >> 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'"
>>
>> Hang on -- just to clarify, something like the following doesn't work
>> (or wouldn't, you suspect, work)?
>>
>> * Start driver domain
>> * Start domU A with no network
>
> My setup is different here.  I include the vif = [... backend=...]
> declaration in my domain config.
>
>> * xl network-attach A backend=drv_dom
>
> So I don't do this step manually.

Right, but you do the detach manually (as well as the subsequent
attach after the driver domain

>
>> * [do some stuff]
>> * xl network-detach A [network devid]
>> * Restart driver domain
>> * xl network-attach A backend=drv_dom
[snip]
> Sorry, I get NO-CARRIER in the just rebooted driver domain.  And the
> interface is still UP in domU A.

Wait, that sounds like a different problem than the one we thought you
were talking about.  You're saying that the driver domain is losing
connection to the *physical* network after reboot?  That sounds more
like an issue with PCI passthrough than with the PV networking
protocol.

So what happens if you do the following:

* Boot your driver domain (but don't connect any guests)
* From your driver domain, ping an off-host IP
* Reboot the driver domain
* Try pinging an off-host IP again

It sounds like maybe the second ping will fail?

 -George

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