vhost-user back ends
vhost-user back ends are way to service the request of VirtIO devices outside of QEMU itself. To do this there are a number of things required.
These are simple stub devices that ensure the VirtIO device is visible
to the guest. The code is mostly boilerplate although each device has
chardev option which specifies the ID of the
device that connects via a socket to the vhost-user daemon.
This is a separate process that is connected to by QEMU via a socket following the Vhost-user Protocol. There are a number of daemons that can be built when enabled by the project although any daemon that meets the specification for a given device can be used.
First start you daemon.
$ virtio-foo --socket-path=/var/run/foo.sock $OTHER_ARGS
The you start your QEMU instance specifying the device, chardev and memory objects.
$ qemu-system-x86_64 \ -m 4096 \ -chardev socket,id=ba1,path=/var/run/foo.sock \ -device vhost-user-foo,chardev=ba1,$OTHER_ARGS \ -object memory-backend-memfd,id=mem,size=4G,share=on \ -numa node,memdev=mem \ ...