1# Vhost-user devices 2 3Crosvm supports [vhost-user] devices for most virtio devices (block, net, etc ) so that device 4emulation can be done outside of the main vmm process. 5 6Here is a diagram showing how vhost-user block device back-end (implementing the actual disk in 7userspace) and a vhost-user block front-end (implementing the device facing the guest OS) in crosvm 8VMM work together. 9 10<!-- Image from https://docs.google.com/presentation/d/1s6wH5L_F8NNiXls5UgWbD34jtBmijoZuiyLu76Fc2NM/edit#slide=id.ge5067b4ec2_0_55 --> 11 12 13 14## How to run 15 16Let's take a block device as an example and see how to start vhost-user devices. 17 18First, start vhost-user block backend with `crosvm devices` command, which waits for a vmm process 19connecting to the socket. 20 21```sh 22# One-time commands to create a disk image. 23fallocate -l 1G disk.img 24mkfs.ext4 disk.img 25 26VHOST_USER_SOCK=/tmp/vhost-user.socket 27 28# Start vhost-user block backend listening on $VHOST_USER_SOCK 29crosvm devices --block vhost=${VHOST_USER_SOCK},path=disk.img 30``` 31 32Then, open another terminal and start a vmm process with `--vhost-user` flag (the frontend). 33 34```sh 35crosvm run \ 36 --vhost-user block,socket="${VHOST_USER_SOCK}" \ 37 <usual crosvm arguments> 38 /path/to/bzImage 39``` 40 41As a result, `disk.img` should be exposed as `/dev/vda` just like with `--block disk.img`. 42 43[vhost-user]: https://qemu-project.gitlab.io/qemu/interop/vhost-user.html 44
