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Re: [libvirt-users] Network interface name of guest via python API



On 19.03.2018 19:07, Laine Stump wrote:
> On 03/19/2018 11:46 AM, Dennis Jacobfeuerborn wrote:
>> Hi,
>> I'm trying to get some basic data from running guests on a libvirt HV
>> but one thing I'm missing is the name of the network interfaces of the
>> guests. I can get the MAC address from the XML but there seems to be no
>> function to actually get the name of the interface.
>>
>> The only function that comes close is this one:
>> https://libvirt.org/html/libvirt-libvirt-domain.html#virDomainInterfaceAddresses
>>
>> This function requires a parameter that I don't really have enough
>> information about.
> 
> Which parameter is that? flags? That seems fairly thoroughly explained
> in the documentation you pointed at.

I'm actually talking about the "source" parameter.

>> What is the best way to enumerate a guests interfaces including the name?
> 
> Assuming you mean the name of the interface *as it appears to the
> guest*... Since the host can't directly know the names of devices on the
> guest, the only way you can learn this is with cooperation from the OS
> running on the guest. One way of getting that cooperation is to make
> sure the guest is running the qemu guest agent (and that libvirt's
> domain config has the proper serial channel configured), then
> virDomainInterfaceAddresses() with the
> VIR_DOMAIN_INTERFACE_ADDRESSES_SRC_AGENT flag will return entries that
> contain the interface name as it appears to the guest (the other modes
> of virDomainInterfaceAddresses will show the names of the tap devices on
> the *host*, not of the interfaces in the guest).
> 
> You can check if your guests are running the qemu guest agent (and try
> out the virDomainInterfaceAddresses() API at the same time) with this
> shell command (run as root on the host):
> 
>    virsh domifaddr $guestname --source agent
> 
> Here is info in the libvirt wiki about installing / configuring the qemu
> guest agent:
> 
>   https://wiki.libvirt.org/page/Qemu_guest_agent
> 
> (I just checked on a Fedora 27 guest that I previously defined with
> virt-manager to use spice for video, I found that virt-manager had
> automatically added the necessary serial channel device
> ("org.qemu.guest_agent.0"), and that the Linux kernel in the guest
> automatically noticed that and setup a guest agent in the guest. It may
> (will) take more work to get the guest agent working for other guest
> OSes, e.g. Windows.)
> 

Assuming that the guest agent is running is not really an option as I
don't really have control over how the guests are installed.
What I'm really interested in is a way to uniquely identify a network
interface.
Let's say I want gather statistics for an interface using
virDomainInterfaceStats() for a guest with multiple interfaces how do I
ensure that I always get the proper stats for the individual interfaces?
If there was an ID for each interface that would be easy but that
doesn't seem to exist and now that I realize that the name apparently is
created on startup of the guest that name might not be a stable
identifier either.
I guess I can (ab)use the MAC address but is this really guaranteed to
exist for each Interface? What about SDN-like setups that don't use
Layer-2 networking at all and set the MAC to something like
"00:00:00:00:00:00"?

Regards,
  Dennis


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