vmm: Make --kernel optional

The kernel path was the only mandatory command line option.
With the addition of the --api-socket option, we can run without a
kernel path and get it later through the API.

Since we can end up with VM configurations that are no longer valid by
default, we need to provide a validation check for it. For now, if the
kernel path is not defined, the VM configuration is invalid.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

src/main.rs

@@ -255,9 +255,7 @@ fn main() {
     let rng = cmd_arguments.value_of("rng").unwrap();
     let serial = cmd_arguments.value_of("serial").unwrap();
 
-    let kernel = cmd_arguments
-        .value_of("kernel")
-        .expect("Missing argument: kernel");
+    let kernel = cmd_arguments.value_of("kernel");
     let cmdline = cmd_arguments.value_of("cmdline");
 
     let disks: Option<Vec<&str>> = cmd_arguments.values_of("disk").map(|x| x.collect());
@@ -332,7 +330,7 @@ fn main() {
         api_socket_path,
         u8::from(&vm_config.cpus),
         vm_config.memory.size >> 20,
-        vm_config.kernel.path,
+        vm_config.kernel,
         vm_config.cmdline.args.as_str(),
         vm_config.disks,
     );
@@ -349,15 +347,17 @@ fn main() {
         }
     };
 
-    // Create and start the VM based off the VM config we just built.
-    let sender = api_request_sender.clone();
-    vmm::vm_create(
-        api_evt.try_clone().unwrap(),
-        api_request_sender,
-        Arc::new(vm_config),
-    )
-    .expect("Could not create the VM");
-    vmm::vm_start(api_evt.try_clone().unwrap(), sender).expect("Could not start the VM");
+    if cmd_arguments.is_present("vm-config") && vm_config.valid() {
+        // Create and start the VM based off the VM config we just built.
+        let sender = api_request_sender.clone();
+        vmm::vm_create(
+            api_evt.try_clone().unwrap(),
+            api_request_sender,
+            Arc::new(vm_config),
+        )
+        .expect("Could not create the VM");
+        vmm::vm_start(api_evt.try_clone().unwrap(), sender).expect("Could not start the VM");
+    }
 
     match vmm_thread.join() {
         Ok(res) => match res {

vmm/src/config.rs

@@ -75,13 +75,15 @@ pub enum Error<'a> {
     ParseVsockCidParam(std::num::ParseIntError),
     /// Failed parsing vsock socket path parameter.
     ParseVsockSockParam,
+    /// Missing kernel configuration
+    ValidateMissingKernelConfig,
 }
 pub type Result<'a, T> = result::Result<T, Error<'a>>;
 
 pub struct VmParams<'a> {
     pub cpus: &'a str,
     pub memory: &'a str,
-    pub kernel: &'a str,
+    pub kernel: Option<&'a str>,
     pub cmdline: Option<&'a str>,
     pub disks: Option<Vec<&'a str>>,
     pub net: Option<Vec<&'a str>>,
@@ -177,14 +179,6 @@ pub struct KernelConfig {
     pub path: PathBuf,
 }
 
-impl KernelConfig {
-    pub fn parse(kernel: &str) -> Result<Self> {
-        Ok(KernelConfig {
-            path: PathBuf::from(kernel),
-        })
-    }
-}
-
 #[derive(Clone)]
 pub struct CmdlineConfig {
     pub args: Cmdline,
@@ -617,7 +611,7 @@ impl VhostUserBlkConfig {
 pub struct VmConfig {
     pub cpus: CpusConfig,
     pub memory: MemoryConfig,
-    pub kernel: KernelConfig,
+    pub kernel: Option<KernelConfig>,
     pub cmdline: CmdlineConfig,
     pub disks: Option<Vec<DiskConfig>>,
     pub net: Option<Vec<NetConfig>>,
@@ -633,6 +627,10 @@ pub struct VmConfig {
 }
 
 impl VmConfig {
+    pub fn valid(&self) -> bool {
+        self.kernel.is_some()
+    }
+
     pub fn parse(vm_params: VmParams) -> Result<Self> {
         let mut disks: Option<Vec<DiskConfig>> = None;
         if let Some(disk_list) = &vm_params.disks {
@@ -712,10 +710,17 @@ impl VmConfig {
             vhost_user_blk = Some(vhost_user_blk_config_list);
         }
 
+        let mut kernel: Option<KernelConfig> = None;
+        if let Some(k) = vm_params.kernel {
+            kernel = Some(KernelConfig {
+                path: PathBuf::from(k),
+            });
+        }
+
         Ok(VmConfig {
             cpus: CpusConfig::parse(vm_params.cpus)?,
             memory: MemoryConfig::parse(vm_params.memory)?,
-            kernel: KernelConfig::parse(vm_params.kernel)?,
+            kernel,
             cmdline: CmdlineConfig::parse(vm_params.cmdline)?,
             disks,
             net,

vmm/src/vm.rs

@@ -463,7 +463,8 @@ fn get_host_cpu_phys_bits() -> u8 {
 impl Vm {
     pub fn new(config: Arc<VmConfig>, exit_evt: EventFd, reset_evt: EventFd) -> Result<Self> {
         let kvm = Kvm::new().map_err(Error::KvmNew)?;
-        let kernel = File::open(&config.kernel.path).map_err(Error::KernelFile)?;
+        let kernel =
+            File::open(&config.kernel.as_ref().unwrap().path).map_err(Error::KernelFile)?;
         let fd = kvm.create_vm().map_err(Error::VmCreate)?;
         let fd = Arc::new(fd);
         let creation_ts = std::time::Instant::now();