vmm: Propagate boot_kernel errors properly

So that our error traces are more meaningful.

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

src/main.rs

@@ -120,5 +120,7 @@ fn main() {
     )
     .unwrap();
 
-    vmm::boot_kernel(vm_config).unwrap();
+    if let Err(e) = vmm::boot_kernel(vm_config) {
+        println!("Guest boot failed: {}", e);
+    }
 }

vmm/src/lib.rs

@@ -6,10 +6,38 @@
 extern crate kvm_ioctls;
 
 use kvm_ioctls::*;
+use std::fmt::{self, Display};
+use std::result;
 
 pub mod vm;
 
-use self::vm::{Result, Vm, VmConfig};
+use self::vm::{Vm, VmConfig};
+
+/// Errors associated with VM management
+#[derive(Debug)]
+pub enum Error {
+    /// Cannot create a new VM.
+    VmNew(vm::Error),
+
+    /// Cannot start a VM.
+    VmStart(vm::Error),
+
+    /// Cannot load a kernel.
+    LoadKernel(vm::Error),
+}
+pub type Result<T> = result::Result<T, Error>;
+
+impl Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        use self::Error::*;
+
+        match self {
+            VmNew(e) => write!(f, "Can not create a new virtual machine: {:?}", e),
+            VmStart(e) => write!(f, "Can not start a new virtual machine: {:?}", e),
+            LoadKernel(e) => write!(f, "Can not load a guest kernel: {:?}", e),
+        }
+    }
+}
 
 struct Vmm {
     kvm: Kvm,
@@ -24,10 +52,10 @@ impl Vmm {
 
 pub fn boot_kernel(config: VmConfig) -> Result<()> {
     let vmm = Vmm::new()?;
-    let mut vm = Vm::new(&vmm.kvm, config)?;
+    let mut vm = Vm::new(&vmm.kvm, config).map_err(Error::VmNew)?;
 
-    let entry = vm.load_kernel()?;
-    vm.start(entry)?;
+    let entry = vm.load_kernel().map_err(Error::LoadKernel)?;
+    vm.start(entry).map_err(Error::VmStart)?;
 
     Ok(())
 }