virtmanager/src/main.rs

// Copyright 2021, The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Android Virt Manager

use android_system_virtmanager::aidl::android::system::virtmanager::IVirtManager::{
    BnVirtManager, IVirtManager,
};
use android_system_virtmanager::aidl::android::system::virtmanager::IVirtualMachine::{
    BnVirtualMachine, IVirtualMachine,
};
use android_system_virtmanager::binder::{self, add_service, Interface, StatusCode, Strong};
use anyhow::{Context, Error};
use log::{debug, error, info};
use serde::{Deserialize, Serialize};
use std::fs::File;
use std::io::{self, BufReader};
use std::process::{Child, Command};
use std::sync::{Arc, Mutex};

/// The first CID to assign to a guest VM managed by the Virt Manager. CIDs lower than this are
/// reserved for the host or other usage.
const FIRST_GUEST_CID: Cid = 10;

const BINDER_SERVICE_IDENTIFIER: &str = "android.system.virtmanager";

/// The unique ID of a VM used (together with a port number) for vsock communication.
type Cid = u32;

/// Configuration for a particular VM to be started.
#[derive(Clone, Debug, Deserialize, Eq, PartialEq, Serialize)]
struct VmConfig {
    kernel: String,
    initrd: Option<String>,
    params: Option<String>,
}

fn main() {
    env_logger::init();
    let state = Arc::new(Mutex::new(State::new()));
    let virt_manager = VirtManager::new(state);
    let virt_manager = BnVirtManager::new_binder(virt_manager);
    add_service(BINDER_SERVICE_IDENTIFIER, virt_manager.as_binder()).unwrap();
    info!("Registered Binder service, joining threadpool.");
    binder::ProcessState::join_thread_pool();
}

#[derive(Debug)]
struct VirtManager {
    state: Arc<Mutex<State>>,
}

impl VirtManager {
    fn new(state: Arc<Mutex<State>>) -> Self {
        VirtManager { state }
    }
}

impl Interface for VirtManager {}

impl IVirtManager for VirtManager {
    /// Create and start a new VM with the given configuration, assigning it the next available CID.
    ///
    /// Returns a binder `IVirtualMachine` object referring to it, as a handle for the client.
    fn startVm(&self, config_path: &str) -> binder::Result<Strong<dyn IVirtualMachine>> {
        let state = &mut *self.state.lock().unwrap();
        let cid = state.next_cid;
        let child = start_vm(config_path, cid)?;
        // TODO(qwandor): keep track of which CIDs are currently in use so that we can reuse them.
        state.next_cid = state.next_cid.checked_add(1).ok_or(StatusCode::UNKNOWN_ERROR)?;
        Ok(VirtualMachine::create(Arc::new(VmInstance::new(child, cid))))
    }
}

/// Implementation of the AIDL IVirtualMachine interface. Used as a handle to a VM.
#[derive(Debug)]
struct VirtualMachine {
    instance: Arc<VmInstance>,
}

impl VirtualMachine {
    fn create(instance: Arc<VmInstance>) -> Strong<dyn IVirtualMachine> {
        let binder = VirtualMachine { instance };
        BnVirtualMachine::new_binder(binder)
    }
}

impl Interface for VirtualMachine {}

impl IVirtualMachine for VirtualMachine {
    fn getCid(&self) -> binder::Result<i32> {
        Ok(self.instance.cid as i32)
    }
}

/// Information about a particular instance of a VM which is running.
#[derive(Debug)]
struct VmInstance {
    /// The crosvm child process.
    child: Child,
    /// The CID assigned to the VM for vsock communication.
    cid: Cid,
}

impl VmInstance {
    /// Create a new `VmInstance` with a single reference for the given process.
    fn new(child: Child, cid: Cid) -> VmInstance {
        VmInstance { child, cid }
    }
}

impl Drop for VmInstance {
    fn drop(&mut self) {
        debug!("Dropping {:?}", self);
        // TODO: Talk to crosvm to shutdown cleanly.
        if let Err(e) = self.child.kill() {
            error!("Error killing crosvm instance: {}", e);
        }
        // We need to wait on the process after killing it to avoid zombies.
        match self.child.wait() {
            Err(e) => error!("Error waiting for crosvm instance to die: {}", e),
            Ok(status) => info!("Crosvm exited with status {}", status),
        }
    }
}

/// The mutable state of the Virt Manager. There should only be one instance of this struct.
#[derive(Debug)]
struct State {
    next_cid: Cid,
}

impl State {
    fn new() -> Self {
        State { next_cid: FIRST_GUEST_CID }
    }
}

/// Start a new VM instance from the given VM config filename. This assumes the VM is not already
/// running.
fn start_vm(config_path: &str, cid: Cid) -> binder::Result<Child> {
    let config = load_vm_config(config_path).map_err(|e| {
        error!("Failed to load VM config {}: {:?}", config_path, e);
        StatusCode::BAD_VALUE
    })?;
    Ok(run_vm(&config, cid).map_err(|e| {
        error!("Failed to start VM {}: {:?}", config_path, e);
        StatusCode::UNKNOWN_ERROR
    })?)
}

/// Load the configuration for the VM with the given ID from a JSON file.
fn load_vm_config(path: &str) -> Result<VmConfig, Error> {
    let file = File::open(path).with_context(|| format!("Failed to open {}", path))?;
    let buffered = BufReader::new(file);
    Ok(serde_json::from_reader(buffered)?)
}

/// Start an instance of `crosvm` to manage a new VM.
fn run_vm(config: &VmConfig, cid: Cid) -> Result<Child, io::Error> {
    let mut command = Command::new("crosvm");
    // TODO(qwandor): Remove --disable-sandbox.
    command.arg("run").arg("--disable-sandbox").arg("--cid").arg(cid.to_string());
    if let Some(initrd) = &config.initrd {
        command.arg("--initrd").arg(initrd);
    }
    if let Some(params) = &config.params {
        command.arg("--params").arg(params);
    }
    command.arg(&config.kernel);
    info!("Running {:?}", command);
    // TODO: Monitor child process, and remove from VM map if it dies.
    command.spawn()
}