Re: [Qemu-devel] -net interface association behavior change in current -git.

[Rob Landley <rob@landley.net>]

On 05/13/2011 01:54 AM, Markus Armbruster wrote:
> Rob Landley <rob@landley.net> writes:
> 
>> On 05/12/2011 09:10 AM, Markus Armbruster wrote:
>>> Rob Landley <rob@landley.net> writes:
>>>
>>>> In 1.14.0, if I did this:
>>>>
>>>>   qemu -net nic,blah -net user -net nic,blah -net tun,blah
>>>>
>>>> Then the first nic would be -net user, and the second nic would be -net
>>>> tun.    In current -git, -net user attaches to the second interface and
>>>> -net tun attaches to the first, I.E. the order is reversed.
>>>>
>>>> Either way the first -nic becomes eth0 in Linux and the second becomes
>>>> eth1 (I can manually assign mac addresses in order to confirm which is
>>>> which), but eth0 used to be the -net user interface and now eth1 is the
>>>> -net user interface.
>>>>
>>>> I bisected this to commit 60c07d933c66c4b30a83b but I don't know why it
>>>> changed the behavior, and I can't find _documentation_ on having
>>>> multiple interfaces transports hooked up to the same qemu instance
>>>> anyway.  (It used to work, but possibly that was an accident?)
>>>>
>>>> Any ideas?
>>>
>>> Does it happen with -device and -netdev as well?
>>>
>>> See docs/qdev-device-use.txt for how to go from -net to -device.
>>
>> Read read read...
>>
>> That seems to be micromanaging PCI bus slot assignment, which isn't
>> changed by this patch.  The cards don't move around, nor does the
>> association between cards and Linux eth0/eth1.  What changes is which
>> virtual LAN each virtual ethernet card is plugged into.  (The virtual
>> cat5 cable coming out of the card moves to a different switch.)
> 
> I didn't mean to tell you "try using -device to juggle PCI addresses".
> I meant to steer you away from QEMU VLANs, to find out whether they're a
> factor in your problem.  Possible, because non-VLAN uses a few different
> code paths in QEMU.  Sorry if I was too terse.
> 
> In general, my advice is stay away from QEMU VLANs.

Ok, now I'm confused.

Before this, I wasn't using them.  Now I am.  What's the reason for
avoiding them?  (Also, I didn't see a way in -device to specify a
network transport, just cards and their properties.  Quite possibly I
missed it...)

>> (The fix was to tag everything with vlan arguments and manually manage
>> the association.)
> 
> Glad you got your problem solved.

Solved, yes.  Understood... less so than I thought, apparently?

Rob