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 and a vhost-user block front-end in 7crosvm VMM work together. 8 9<!-- Image from https://docs.google.com/presentation/d/1s6wH5L_F8NNiXls5UgWbD34jtBmijoZuiyLu76Fc2NM/edit#slide=id.ge5067b4ec2_0_55 --> 10 11 12 13## How to run 14 15Let's take a block device as an example and see how to start vhost-user devices. 16 17First, start vhost-user block backend with `crosvm devices` command, which waits for a vmm process 18connecting to the socket. 19 20```sh 21# One-time commands to create a disk image. 22fallocate -l 1G disk.img 23mkfs.ext4 disk.img 24 25VHOST_USER_SOCK=/tmp/vhost-user.socket 26 27# Start vhost-user block backend listening on $VHOST_USER_SOCK 28crosvm devices --block vhost=${VHOST_USER_SOCK},path=disk.img 29``` 30 31Then, open another terminal and start a vmm process with `--vhost-user-blk` flag. 32 33```sh 34crosvm run \ 35 --vhost-user-blk "${VHOST_USER_SOCK}" \ 36 <usual crosvm arguments> 37 /path/to/bzImage 38``` 39 40As a result, `disk.img` should be exposed as `/dev/vda` just like with `--block disk.img`. 41 42[vhost-user]: https://qemu.readthedocs.io/en/latest/interop/vhost-user.html 43
