Re: -nic model=rocker causes qemu to abort

[Thomas Huth <thuth@redhat.com>]

On 25/05/2020 21.46, Michael Tokarev wrote:
> 25.05.2020 21:45, Thomas Huth wrote:
>> On 29/04/2020 18.43, Michael Tokarev wrote:
>>> Hi!
>>>
>>> Just a fun case of (invalid) usage of qemu-system command line.
>>> Someone tried -nic model=rocker, and qemu does this:
>>>
>>>  Unexpected error in object_property_find() at /build/qemu/git/qom/object.c:1029:
>>>  qemu-system-x86_64: Property '.mac' not found
>>>  Aborted
>>>
>>> This happens after this commit:
>>>
>>> commit 52310c3fa7dc854dd2376ae8a518141abcdb78f3
>>> Author: Paolo Bonzini <pbonzini@redhat.com>
>>> Date:   Fri Mar 2 10:30:50 2018 +0100
>>>
>>>     net: allow using any PCI NICs in -net or -nic
>>>
>>> Previously rocker rightly wasn't usable as a nic model,
>>> and after this commit it is now possible.
>>>
>>> While I agree this is invalid usage, perhaps qemu should not
>>> abort like this?  Maybe it should check the required property
>>> too, before allowing this device to be a nic model?
>>
>> QEMU theoretically should never abort() - abort() means there is
>> something wrong in the code ... so we should definitely fix this by
>> other means. Some questions:
>>
>> 1) How is that rocker device normally used? Similar to a normal network
>> card? Or completely different?
> 
> Nope, this is not a network card, it is a network SWITCH, used as a
> regular PCI device, not network-specific. Hence the problem at hand, -
> before the patch this device weren't "nic-able", so to say, because
> while it is network-related PCI device, it is not a NIC.
> 
> I guess while building a list of "nic-able" cards, we should skip some
> "nic-alike" devices and use some more specific criteria. Not everything
> which is network-related is a regular NIC.

Ok, thanks for the explanation! So looking at the properties of the
rocker and real NIC devices again, I think the solution might be simple:
For -nic/-net, we should only consider devices that have a "netdev"
property. I'll try to write a patch when I've got some spare minutes...

 Thomas