devices: virtio: Initial implementation of virtio-video device

This CL adds a fundamental part of the virtio video device, which will
be shared between the encoder and the decoder.
Both devices uses the virtio-video protocol proposed as RFC v3 [1,2].
The corresponding driver code is at CL:2060327 and its children CLs.

The actual decoding and encoding logic will be implemented in different

[1]: mail:
[2]: PDF:

BUG=b:147465619, b:140082257
TEST=cargo check --features=video-decoder,video-encoder
TEST=ARCVM started with --video-decoder --video-encoder

Cq-Depend: chromium:2203997
Change-Id: I01999eea218ba0f3aaed1558ca2311a57d0c6819
Reviewed-by: Keiichi Watanabe <>
Tested-by: Keiichi Watanabe <>
Tested-by: kokoro <>
Commit-Queue: Keiichi Watanabe <>
22 files changed
tree: 11bc695e179762b6eac26302e6b89db55b251dba
  1. aarch64/
  2. acpi_tables/
  3. arch/
  4. assertions/
  5. async_core/
  6. bin/
  7. bit_field/
  8. cros_async/
  9. crosvm_plugin/
  10. data_model/
  11. devices/
  12. disk/
  13. docker/
  14. docs/
  15. enumn/
  16. fuzz/
  17. gpu_buffer/
  18. gpu_display/
  19. gpu_renderer/
  20. hypervisor/
  21. io_jail/
  22. io_uring/
  23. kernel_cmdline/
  24. kernel_loader/
  25. kokoro/
  26. kvm/
  27. kvm_sys/
  28. linux_input_sys/
  29. msg_socket/
  30. net_sys/
  31. net_util/
  32. p9/
  33. protos/
  34. qcow_utils/
  35. rand_ish/
  36. resources/
  37. seccomp/
  38. src/
  39. sync/
  40. sys_util/
  41. syscall_defines/
  42. tempfile/
  43. tests/
  44. tpm2/
  45. tpm2-sys/
  46. usb_sys/
  47. usb_util/
  48. vfio_sys/
  49. vhost/
  50. virtio_sys/
  51. vm_control/
  52. x86_64/
  53. .dockerignore
  54. .gitignore
  55. .gitmodules
  56. .rustfmt.toml
  58. Cargo.lock
  59. Cargo.toml
  63. OWNERS
  65. rust-toolchain

crosvm - The Chrome OS Virtual Machine Monitor

This component, known as crosvm, runs untrusted operating systems along with virtualized devices. This only runs VMs through the Linux's KVM interface. What makes crosvm unique is a focus on safety within the programming language and a sandbox around the virtual devices to protect the kernel from attack in case of an exploit in the devices.


The channel #crosvm on freenode is used for technical discussion related to crosvm development and integration.

Getting started

Building for CrOS

crosvm on Chromium OS is built with Portage, so it follows the same general workflow as any cros_workon package. The full package name is chromeos-base/crosvm.

See the Chromium OS developer guide for more on how to build and deploy with Portage.

Building with Docker

See the README from the docker subdirectory to learn how to build crosvm in enviroments outside of the Chrome OS chroot.

Building for Linux

NOTE: Building for Linux natively is new and not fully supported.

First, set up depot_tools and use repo to sync down the crosvm source tree. This is a subset of the entire Chromium OS manifest with just enough repos to build crosvm.

mkdir crosvm
cd crosvm
repo init -g crosvm -u --repo-url=
repo sync

A basic crosvm build links against libcap and libfdt. On a Debian-based system, you can install libcap-dev and libfdt-dev.

Handy Debian one-liner for all build and runtime deps, particularly if you're running Crostini:

sudo apt install build-essential libcap-dev libfdt-dev pkg-config python

Known issues:

  • Seccomp policy files have hardcoded absolute paths. You can either fix up the paths locally, or set up an awesome hacky symlink: sudo mkdir /usr/share/policy && sudo ln -s /path/to/crosvm/seccomp/x86_64 /usr/share/policy/crosvm. We'll eventually build the precompiled policies into the crosvm binary.
  • Devices can‘t be jailed if /var/empty doesn’t exist. sudo mkdir -p /var/empty to work around this for now.

And that's it! You should be able to cargo build/run/test.


To see the usage information for your version of crosvm, run crosvm or crosvm run --help.

Boot a Kernel

To run a very basic VM with just a kernel and default devices:

$ crosvm run "${KERNEL_PATH}"

The uncompressed kernel image, also known as vmlinux, can be found in your kernel build directory in the case of x86 at arch/x86/boot/compressed/vmlinux.


In most cases, you will want to give the VM a virtual block device to use as a root file system:

$ crosvm run -r "${ROOT_IMAGE}" "${KERNEL_PATH}"

The root image must be a path to a disk image formatted in a way that the kernel can read. Typically this is a squashfs image made with mksquashfs or an ext4 image made with mkfs.ext4. By using the -r argument, the kernel is automatically told to use that image as the root, and therefore can only be given once. More disks can be given with -d or --rwdisk if a writable disk is desired.

To run crosvm with a writable rootfs:

WARNING: Writable disks are at risk of corruption by a malicious or malfunctioning guest OS.

crosvm run --rwdisk "${ROOT_IMAGE}" -p "root=/dev/vda" vmlinux

NOTE: If more disks arguments are added prior to the desired rootfs image, the root=/dev/vda must be adjusted to the appropriate letter.

Control Socket

If the control socket was enabled with -s, the main process can be controlled while crosvm is running. To tell crosvm to stop and exit, for example:

NOTE: If the socket path given is for a directory, a socket name underneath that path will be generated based on crosvm's PID.

$ crosvm run -s /run/crosvm.sock ${USUAL_CROSVM_ARGS}
    <in another shell>
$ crosvm stop /run/crosvm.sock

WARNING: The guest OS will not be notified or gracefully shutdown.

This will cause the original crosvm process to exit in an orderly fashion, allowing it to clean up any OS resources that might have stuck around if crosvm were terminated early.

Multiprocess Mode

By default crosvm runs in multiprocess mode. Each device that supports running inside of a sandbox will run in a jailed child process of crosvm. The appropriate minijail seccomp policy files must be present either in /usr/share/policy/crosvm or in the path specified by the --seccomp-policy-dir argument. The sandbox can be disabled for testing with the --disable-sandbox option.

Virtio Wayland

Virtio Wayland support requires special support on the part of the guest and as such is unlikely to work out of the box unless you are using a Chrome OS kernel along with a termina rootfs.

To use it, ensure that the XDG_RUNTIME_DIR enviroment variable is set and that the path $XDG_RUNTIME_DIR/wayland-0 points to the socket of the Wayland compositor you would like the guest to use.


The following are crosvm's default arguments and how to override them.

  • 256MB of memory (set with -m)
  • 1 virtual CPU (set with -c)
  • no block devices (set with -r, -d, or --rwdisk)
  • no network (set with --host_ip, --netmask, and --mac)
  • virtio wayland support if XDG_RUNTIME_DIR enviroment variable is set (disable with --no-wl)
  • only the kernel arguments necessary to run with the supported devices (add more with -p)
  • run in multiprocess mode (run in single process mode with --disable-sandbox)
  • no control socket (set with -s)

System Requirements

A Linux kernel with KVM support (check for /dev/kvm) is required to run crosvm. In order to run certain devices, there are additional system requirements:

  • virtio-wayland - The memfd_create syscall, introduced in Linux 3.17, and a Wayland compositor.
  • vsock - Host Linux kernel with vhost-vsock support, introduced in Linux 4.8.
  • multiprocess - Host Linux kernel with seccomp-bpf and Linux namespacing support.
  • virtio-net - Host Linux kernel with TUN/TAP support (check for /dev/net/tun) and running with CAP_NET_ADMIN privileges.

Emulated Devices

CMOS/RTCUsed to get the current calendar time.
i8042Used by the guest kernel to exit crosvm.
serialx86 I/O port driven serial devices that print to stdout and take input from stdin.
virtio-blockBasic read/write block device.
virtio-netDevice to interface the host and guest networks.
virtio-rngEntropy source used to seed guest OS's entropy pool.
virtio-vsockEnabled VSOCKs for the guests.
virtio-waylandAllowed guest to use host Wayland socket.


Code Health


There are no automated tests run before code is committed to crosvm. In order to maintain sanity, please execute build_test before submitting code for review. All tests should be passing or ignored and there should be no compiler warnings or errors. All supported architectures are built, but only tests for x86_64 are run. In order to build everything without failures, sysroots must be supplied for each architecture. See build_test -h for more information.


All code should be formatted with rustfmt. We have a script that applies rustfmt to all Rust code in the crosvm repo: please run bin/fmt before checking in a change. This is different from cargo fmt --all which formats multiple crates but a single workspace only; crosvm consists of multiple workspaces.


With a few exceptions, external dependencies inside of the Cargo.toml files are not allowed. The reason being that community made crates tend to explode the binary size by including dozens of transitive dependencies. All these dependencies also must be reviewed to ensure their suitability to the crosvm project. Currently allowed crates are:

  • cc - Build time dependency needed to build C source code used in crosvm.
  • libc - Required to use the standard library, this crate is a simple wrapper around libc's symbols.

Code Overview

The crosvm source code is written in Rust and C. To build, crosvm generally requires the most recent stable version of rustc.

Source code is organized into crates, each with their own unit tests. These crates are:

  • crosvm - The top-level binary front-end for using crosvm.
  • devices - Virtual devices exposed to the guest OS.
  • io_jail - Creates jailed process using libminijail.
  • kernel_loader - Loads elf64 kernel files to a slice of memory.
  • kvm_sys - Low-level (mostly) auto-generated structures and constants for using KVM.
  • kvm - Unsafe, low-level wrapper code for using kvm_sys.
  • net_sys - Low-level (mostly) auto-generated structures and constants for creating TUN/TAP devices.
  • net_util - Wrapper for creating TUN/TAP devices.
  • sys_util - Mostly safe wrappers for small system facilities such as eventfd or syslog.
  • syscall_defines - Lists of syscall numbers in each architecture used to make syscalls not supported in libc.
  • vhost - Wrappers for creating vhost based devices.
  • virtio_sys - Low-level (mostly) auto-generated structures and constants for interfacing with kernel vhost support.
  • vm_control - IPC for the VM.
  • x86_64 - Support code specific to 64 bit intel machines.

The seccomp folder contains minijail seccomp policy files for each sandboxed device. Because some syscalls vary by architecture, the seccomp policies are split by architecture.