Features/VirtioVsock

virtio-vsock is a host/guest communications device. It allows applications in the guest and host to communicate. This can be used to implement hypervisor services and guest agents (like qemu-guest-agent or SPICE vdagent).

• POSIX Sockets API so existing networking applications require minimal modification (unlike virtio-serial char devices)
• Listen sockets can accept connections from multiple clients (unlike virtio-serial char devices)
• No address configuration required inside the guest
• No Ethernet or TCP/IP for a reduced attack surface for hypervisor services
• Can be used with VMs that have no network interfaces

Sockets are created with the AF_VSOCK address family. The SOCK_STREAM socket type is currently implemented for in-order, guaranteed stream semantics.

Code

• Virtio specification: HTML or virtio.git
• Linux kernel: Available since Linux 4.8, or see stefanha's linux.git
• QEMU: Available in QEMU 2.8, or see stefanha's qemu.git
• netcat-like utility: nc-vsock

Packages

• Fedora 24 copr repo

Quickstart

QEMU:

 $ git clone git://git.qemu-project.org/qemu.git
 $ cd qemu
 $ ./configure --target-list=x86_64-softmmu
 $ make

Linux:

 $ git clone https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
 $ cd linux
 $ cp /boot/config-$(uname -r) .config
 $ make menuconfig # select CONFIG_VHOST_VSOCK=m and CONFIG_VIRTIO_VSOCKETS=m
 $ make install modules_install

To use vhost_vsock.ko you must boot into the new host kernel and modprobe vhost_vsock.

The guest should also use the kernel so that modprobe virtio_transport can load the vsock guest driver.

For details on host and guest boot, see go.sh. Use nc-vsock 2 1234 inside the guest to connect to vsock port 1234 on the host. Use nc-vsock -l 1234 on the host to listen on that port.

Testing

The vhost-vsock-test qtest replays packets from a JSON file and verifies that the expected reply is received.

The JSON test file format is described in a README.

 $ cd qemu
 $ make -j4
 $ make tests/vhost-vsock-test
 $ sudo QTEST_QEMU_BINARY=x86_64-softmmu/qemu-system-x86_64 QTEST_QEMU_IMG=qemu-img MALLOC_PERTURB_=${MALLOC_PERTURB_:-$((RANDOM % 255 + 1))} gtester -k --verbose -m=quick tests/vhost-vsock-test -o /dev/stderr

Create and edit test cases in tests/vhost-vsock-test-data/*.json.

Links

• KVM Forum 2015 presentation: virtio-vsock: Zero-configuration host/guest communication (pdf)
• Connectathon 2016 presentation: NFS over virtio-vsock: Host/guest file sharing for virtual machines (pdf)