Avi Kivity wrote:
quoted text
> On 10/01/2009 08:06 PM, Jim Paris wrote:
>> That's what I do.  Just as a warning, if you're using the libvirt
>> packages from Debian unstable, make sure you also install
>> linux-libc-dev from unstable before building qemu-kvm.
>>
>> Otherwise, virtio networking will fail.  The reason is that qemu-kvm
>> will be built against the Lenny linux-libc-dev which does not have
>> IFF_VNET_HDR, while the libvirt was built against a newer
>> linux-libc-dev that did define IFF_VNET_HDR.  If they don't agree then
>> things break.
>
> Isn't that a libvirt bug?  libvirt shouldn't assume qemu supports  
> IFF_VNET_HDR just because it sees it.

Probably, but I think it has no way of knowing, because qemu doesn't
report whether it supports it.

  http://libvirt.org/git/?p=libvirt.git;a=commit;h=b4f62abbf1191c8fbab3306b4bf2f2567e18067f

"However, we need to be careful to only set the flag when a) QEMU has
support for this ABI and b) the value of the flag is queryable using
the TUNGETIFF ioctl.

It's nearly five months since kvm-74 - the first KVM release with this
feature - was released. Up until now, we've not added libvirt support
because there is no clean way to detect support for this in QEMU at
runtime. A brief attempt to add a "info capabilities" monitor command
to QEMU floundered. Perfect is the enemy of good enough. Probing the
KVM version will suffice for now."

-jim

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