[libvirt] how to use macvtap in kvm guest

[Laine Stump]

Please do not top post in replies - make your replies to questions 
inline, it makes following the conversation *much* easier.

On 12/09/2011 02:00 AM, Amit Tewari wrote:
>
> Hi,
>
> No guest can not  get ip.
>
> When I do ifup eth0 it give error device not found.
>
> Hostos=rhel 6.x86_64
>
> Guest os= rhel 6.x86_64
>
> Libvirt =0.8.7
>
> Macvtap driver is loaded.
>
> Qemu-kvm= 0.12.1.2
>
> i think this error is creating problem
>
> macvtap0:no ipv6 routers present
>
> ------------------------------------------------------------------------
>
> *From:*xhu [mailto:xhu at redhat.com]
> *Sent:* Friday, December 09, 2011 10:53 AM
> *To:* Amit Tewari
> *Cc:* libvir-list at redhat.com
> *Subject:* Re: [libvirt] how to use macvtap in kvm guest
>
> On 12/09/2011 12:28 PM, Amit Tewari wrote:
>
> Hi
>
> I am creating macvtap0 interface on my eth1 interface.
>
> ip link show macvtap0
>
> 133: macvtap0 at eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc 
> mq state UNKNOWN qlen 500
>
>     link/ether 3e:63:18:f3:49:63 brd ff:ff:ff:ff:ff:ff
>

Are you saying that you're manually creating a macvtap0 device outside 
of libvirt? Or are you just showing us the macvtap device that libvirt 
is creating?


> guest interface file-
>
> <interface type='direct'>
>
> <mac address='3e:63:18:f3:49:63'/>
>
> <source dev='eth0' mode='bridge'/>
>
> <model type='virtio'/>
>
> <address type='pci' domain='0x0000' bus='0x00' slot='0x02' 
> function='0x0'/>
>
> </interface>
>
> Now when I do-
>
> Virsh define guest works fine
>
> But when I do virsh start guest
>
> can guest gain ip?
>
> Dmesg shows error
>


dmesg on the host, correct?


> macvtap0:no ipv6 routers present
>
> libvirtd[24907]: segfault at 0 ip 0000003e22280062 sp 00007fd3057f8cb8 
> error 4 in libc-2.12.so[3e22200000+187000]
>

Does this segfault happen every time? If you have a RHEL subscription, 
you should open a ticket with Red Hat support.

Have you rebooted the host since you first encountered this error - I 
have seen cases where old stale macvtap devices stuck around, preventing 
the creation of a new device with the same name.

If it's feasible to upgrade, you may want to do so - RHEL 6.2 (with 
libvirt-0.9.4) was released on Wednesday.

> and even if guest starts its eth interface is not created
>
> could you provide your host os, guest os, libvirt, qemu-kvm version?
>

Also useful for debugging - the last qemu command listed in 
/var/log/libvirt/qemu/$guestname.log

Additionally, the output of "virsh dumpxml $guestname" (in particular 
the <interface> section) while the guest is running (this will be 
different from the "inactive" version you've provided above).

> it is fine as i tried, no segment fault message and the guest can get ip.
>
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