Re: [Qemu-devel] [PATCH] add mac address collision checking for device_add & pci_add

[Stefan Hajnoczi]

On Mon, Nov 12, 2012 at 12:49 PM, Lin Ma <address@hidden> wrote:
>>>> Paolo Bonzini <address@hidden> 11/12/12 7:27 PM >>>
>
> Il 12/11/2012 12:18, Daniel P. Berrange ha scritto:
>>> > QEMU doesn't check if there are mac collisions when adding nics.
>>> > It causes mac address collisions in guest if adding the nics which
>>> > include existing physical address.
>>> > This patch fixes the issue.
>> I understand the issue, but are there not use cases where it is
>> reasonable to have multiple NICs with the same MAC address ? To
>> me this kind of policy enforcement belongs at a higher level in
>> the mgmt stack.
>
>>>>I agree.
>
> Yes, Users won't intentionally add multiple NICs with the same MAC address.
> But what if there is typos in command-line or upper layer applications pass
> a conflicting mac option to qemu?
> We can't fully trust other applications to do this. So qemu shouldn't depend
> on other applications for the verifying mac.
> No matter upper layer applications verify mac or not, qemu should check the
> mac itself again to ensure the correctness.

It's perfectly okay to use the same MAC address on multiple cards from
a hardware emulation perspective (which is the scope of QEMU).

Higher level tools can perform this check if they want this policy.

Stefan