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Re: [libvirt] [question]Is there a good way to get the mac of guest interface after I attached it to a guest



On 01/24/2014 03:55 PM, Martin Kletzander wrote:
On Fri, Jan 24, 2014 at 10:37:20AM +0800, Sheldon wrote:
Now I working on a new KVM management tool base on html5 and libvirt

we will support a REST API for detach and attach guest interface.

we want to use mac as the identifier of the network interface.

That meas we should get the mac after the user create a interface.
also other people may be doing the exact same thing at the exact same
time to create a interface.


Here are the demo codes:

dom = self._get_vm(vm)
xml = """
<interface type='network'>
<source network='default'/>
</interface>
"""
dom.attachDeviceFlags(xml, libvirt.VIR_DOMAIN_AFFECT_CURRENT)
# now I want to get the mac, how to get it?

You have to parse the XML back and find it.

I have check libvirt use this code to generate a mac address.
does libvirt can gurantee that the MAC address generated is unique?

No, as mentioned in the second subthread, the XML you provided is
incomplete and can cause address clashing.

So te best answer to your question in $SUBJ would be "generate it
yourself and add it to the XML before attaching".


now I define a  mac address  generator in our management tool.
it will generate a mac and assign it xml before create the interface.

+        def randomMAC():
+            mac = [0x52, 0x54, 0x00,
+                   random.randint(0x00, 0x7f),
+                   random.randint(0x00, 0xff),
+                   random.randint(0x00, 0xff)]
+        mac = randomMAC()

+        xml = """
+        <interface type='network'>
+        <source network='default'/>
+        <mac address='%s' >
+        </interface>
+        """ % mac

should I gurantee that the MAC address generated is unique by myself?
check every interface mac of every guest, and make sure no address clashing?


I wonder can libvirt support a API to generate mac address?


Martin

void virMacAddrGenerate(const unsigned char prefix[VIR_MAC_PREFIX_BUFLEN],
virMacAddrPtr addr)
{
addr->addr[0] = prefix[0];
addr->addr[1] = prefix[1];
addr->addr[2] = prefix[2];
addr->addr[3] = virRandomBits(8);
addr->addr[4] = virRandomBits(8);
addr->addr[5] = virRandomBits(8);
}
libvirt also use the KVM prefix as default as it's in the privately
administered range:
52:54:00:XX:XX:XX



--
Thanks and best regards!

Sheldon Feng(冯少合)<shaohef linux vnet ibm com>
IBM Linux Technology Center

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--
Thanks and best regards!

Sheldon Feng(冯少合)<shaohef linux vnet ibm com>
IBM Linux Technology Center


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