[libvirt] [PATCH RFC] Add support for QEMU vhost-user feature

[Daniel P. Berrange]

On Thu, Jun 05, 2014 at 05:09:02PM +0300, Laine Stump wrote:
> Daniel pointed out that qemu actually accepts any generic character
> device to connect to, and it makes sense to support this by using
> virDomainChrSourceDefPtr. However, the parse function for
> virDomainChrSourceDef requires that the type of character device be
> already parsed and set in the object, implying that it needs to be in
> the config somewhere outside of the <source> element itself.
> 
> Related to that, I'm wondering if maybe instead of setting the type of
> <interface> to the very specific "vhostuser", maybe it could be set to
> the type of character device ("socket", "tcp", etc), and the fact that
> vhostuser is used could be specified in exactly the same way that
> vhost-net is turned on for tap devices - with <driver name="vhost"/>. So
> for example, you would have this:
> 
> 
>   <interface type='unix'> <!-- for a unix domain socket -->
>     <model type='virtio'/>
>     <driver name='vhost'/>
>     <source path='xyzzy' mode='server'/>
>     ...
>   </interface>

The problem with this is that some of the chardev 'type' options
clash with some of the interface 'type' options, so I think we
must keep them separated. I do agree that 'vhostuser' is a somewhat
QEMU specific name - at least with 'tap' this was a common terminology
across multiple OS and projects. This is really a variant on 'tap'
which is avoiding use of kernel devices. To perhaps we should call
this new mode 'usertap' ? Or another idea would be to call it 'tapstream'
eg

   <interface type='usertap'>
     <model type='virtio'/>
     <driver name='vhost'/>
     <source type='unix'>
        ...chardev source schema...
     </source>
   </interface>



Regards,
Daniel
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