ARCVM mojo proxy

ARCVM mojo proxy proxies data sent over file descriptors used for mojo communication between the host and the guest.

        Chrome
           |
     Host mojo proxy
           |
        crosvm
           |
 +---------+----------+
 |ARCVM    |          |
 |         |          |
 |    Guest kernel    |
 |         |          |
 |  Guest mojo proxy  |
 |         |          |
 | ARC bridge service |
 |                    |
 +--------------------+

virtio-wl connection initialization

1. In the guest VM, the guest mojo proxy process creates a named virtio-wl context whose name is “mojo”.
2. The guest kernel sends this request to crosvm's virtio-wl process in the host.
3. In the host, crosvm's virtio-wl process forwards this request to a named UNIX domain socket /run/arcvm/mojo/mojo-proxy.sock.
4. The host mojo proxy process listens on /run/arcvm/mojo/mojo-proxy.sock and accepts the connection.
5. Now the guest mojo proxy process and the host mojo proxy process are connected by virtio-wl. Data sent to the virtio-wl context in the guest can be received by /run/arcvm/mojo-proxy.sock in the host and vice versa.

Mojo channel initialization

1. In the guest VM, the ARC bridge service connects to a named UNIX domain socket /var/run/chrome/arc_bridge.sock.
2. The guest mojo proxy process listens on /var/run/chrome/arc_bridge.sock and accepts the connection.
3. The guest mojo proxy process sends the host mojo proxy process a connection request.
4. In the host, the host mojo proxy process handles the connection request by connecting to a named UNIX domain socket /run/chrome/arc_bridge.sock.
5. The chrome browser process listens on /run/chrome/arc_bridge.sock and accepts the connection.
6. Now the ARC bridge service in the guest VM and the chrome browser process in the host are connected by a proxied UNIX domain socket via mojo proxy processes.