On Tue, Nov 19, 2013 at 11:17:40AM +0100, Antonios Motakis wrote: > There have been discussions before on these lists on the topic of > connecting a QEMU guest running a virtio_net driver, with an external > userspace ethernet switch (Snabbswitch in particular). The essential > requirement in this is to put the virtio backend in the external > userspace process. > > The preferred direction should be similar to vhost, with the main > difference of the control mechanism being a unix domain socket instead > of an ioctl interface, and of course placing the backend in an > userspace process instead the kernel. > > Since we are pursuing this direction,we would like to share a more > detailed description of the architecture we are working on. Any > feedback is most welcome. It is available here: > http://www.virtualopensystems.com/media/snabbswitch/rfc_snabbswitch_qemu.pdf
It sounds like you are proposing an interprocess virtio device interface. QEMU's virtio-pci emulation calls into a new vapp virtio device inside QEMU, which then forwards virtio device calls to the vapp process. This is pretty different from vhost. vhost only puts rx/tx handling in the kernel. Other functionality is handled by plain old QEMU virtio device emulation (e.g. virtio-net ctrl virtqueue). In the past device plugin interfaces have been rejected by the community because they can lead to lower code quality (out-of-tree devices) and an avenue to bypass the software license. So what's the alternative? Reuse as much of the vhost approach as possible and define a userspace network I/O interface instead of a device plugin interface. Stefan
