Re: [PATCH] kvm: qemu: Handle tap fds with IFF_VNET_HDR

[Anthony Liguori <anthony@codemonkey.ws>]

Avi Kivity wrote:
> Anthony Liguori wrote:
>   
>> Mark McLoughlin wrote:
>>     
>>> Allow users to pass an IFF_VNET_HDR tap fd via "-net tap,fd=X"
>>> by querying the fd with the recently added TUNGETIFF ioctl() to
>>> see if IFF_VNET_HDR has been enabled.
>>>
>>> Note: users wishing to pass an IFF_VNET_HDR tap fd to qemu
>>> should check both that a) this version of qemu can handle
>>> such an fd and b) that the TUNGETIFF ioctl() is available in
>>> the running kernel.
>>>
>>> We add a comment to the "qemu -help" output to indicate to
>>> users that this version of qemu supports IFF_VNET_HDR.
>>>   
>>>       
>> The -help output is not a supported interface.  An info command in the
>> monitor would be a better way to detect this.
>>
>>     
>
> You need to know this before you create a virtual machine.  I suggested
> a 'qemu -capabilities' thing to describe what this qemu can do.
>   

$ echo -e 'info version\nquit' | qemu-system-x86_64 -S -hda /dev/null 
-monitor stdio -vnc none

Okay, a little hacky, but so are a lot of things that libvirt is doing :-)

A proper -version flag that also has a bitmap of 'features' may be 
reasonable too.

Regards,

Anthony Liguori