Cloud Hypervisor v0.7.0 Released!

Posted April 30, 2020 by Cloud Hypervisor Team ‐ 3 min read

This release has been tracked through the 0.7.0 project.

Highlights for cloud-hypervisor version 0.7.0 include:

Block, Network, Persistent Memory (PMEM), VirtioFS and Vsock hotplug

Further to our effort to support modifying a running guest we now support hotplug and unplug of the following virtio backed devices: block, network, pmem, virtio-fs and vsock. This functionality is available on the (default) PCI based tranport and is exposed through the HTTP API. The ch-remote utility provides a CLI for adding or removing these device types after the VM has booted. User can use the id parameter on the devices to choose names for devices to ease their removal.

Alternative libc Support

Cloud Hypervisor can now be compiled with the musl C library and this release contains a static binary compiled using that toolchain.

Multithreaded Multi Queued vhost-user Backends

The vhost-user backends for network and block support that are shipped by Cloud Hypervisor have been enhanced to support multiple threads and queues to improve throughput. These backends are used automatically if vhost_user=true is passed when the devices are created.

Initial RamFS Support

By passing the --initramfs command line option the user can specify a file to be loaded into the guest memory to be used as the kernel initial filesystem. This is usually used to allow the loading of drivers needed to be able to access the real root filesystem but it can also be used standalone for a very minimal image.

Alternative Memory Hotplug: virtio-mem

As well as supporting ACPI based hotplug Cloud Hypervisor now supports using the virtio-mem hotplug alternative. This can be controlled by the hotplug_method parameter on the --memory command line option. It currently requires kernel patches to be able to support it.

Seccomp Sandboxing

Cloud Hypervisor now has support for restricting the system calls that the process can use via the seccomp security API. This on by default and is controlled by the --seccomp command line option.

Updated Distribution Support

With the release of Ubuntu 20.04 we have added that to the list of supported distributions and is part of our regular testing programme.

Command Line and API Changes

This is non exhaustive list of HTTP API and command line changes

  • New id fields added for devices to allow them to be named to ease removal. If no name is specified the VMM chooses one.
  • Use --memory’s shared and hugepages controls for determining backing memory instead of providing a path.
  • The --vsock parameter only takes one device as the Linux kernel only supports a single Vsock device. The REST API has removed the vector for this option and replaced it with a single optional field.
  • There is enhanced validation of the command line and API provided configurations to ensure that the provided options are compatible e.g. that shared memory is in use if any attempt is made to used a vhost-user backed device.
  • ch-remote has added add-disk, add-fs, add-net, add-pmem and add-vsock subcommands. For removal remove-device is used. The REST API has appropriate new HTTP endpoints too.
  • Specifying a size with --pmem is no longer required and instead the size will be obtained from the file. A discard_writes option has also been added to provide the equivalent of a read-only file.
  • The parameters to --block-backend have been changed to more closely align with those used by --disk.


Many thanks to everyone who has contributed to our 0.7.0 release including some new faces.


See the GitHub Release for the release assets.