vmm: Make serial port controllable via command line

Add a "--serial" command line that takes as input either "off", "tty"
(default and current behaviour) and "file=/path/to/file".

When "--serial off" is used the serial device is not added to the VM
configuration at all.

Integration tests added that check for interrupts present (or not) and
that when sending to a file the file contains the expected serial
output.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vmm/src/config.rs

@@ -50,6 +50,8 @@ pub enum Error<'a> {
     ParsePmemFileParam,
     /// Failed parsing size parameter.
     ParseSizeParam(std::num::ParseIntError),
+    /// Failed parsing serial parameter.
+    ParseSerialParam,
 }
 pub type Result<'a, T> = result::Result<T, Error<'a>>;
 
@@ -63,6 +65,7 @@ pub struct VmParams<'a> {
     pub rng: &'a str,
     pub fs: Option<Vec<&'a str>>,
     pub pmem: Option<Vec<&'a str>>,
+    pub serial: &'a str,
 }
 
 fn parse_size(size: &str) -> Result<u64> {
@@ -338,6 +341,41 @@ impl<'a> PmemConfig<'a> {
     }
 }
 
+#[derive(PartialEq)]
+pub enum SerialOutputMode {
+    Off,
+    Tty,
+    File,
+}
+
+pub struct SerialConfig<'a> {
+    pub file: Option<&'a Path>,
+    pub mode: SerialOutputMode,
+}
+
+impl<'a> SerialConfig<'a> {
+    pub fn parse(param: &'a str) -> Result<Self> {
+        if param == "off" {
+            Ok(Self {
+                mode: SerialOutputMode::Off,
+                file: None,
+            })
+        } else if param == "tty" {
+            Ok(Self {
+                mode: SerialOutputMode::Tty,
+                file: None,
+            })
+        } else if param.starts_with("file=") {
+            Ok(Self {
+                mode: SerialOutputMode::File,
+                file: Some(Path::new(&param[5..])),
+            })
+        } else {
+            Err(Error::ParseSerialParam)
+        }
+    }
+}
+
 pub struct VmConfig<'a> {
     pub cpus: CpusConfig,
     pub memory: MemoryConfig<'a>,
@@ -348,6 +386,7 @@ pub struct VmConfig<'a> {
     pub rng: RngConfig<'a>,
     pub fs: Option<Vec<FsConfig<'a>>>,
     pub pmem: Option<Vec<PmemConfig<'a>>>,
+    pub serial: SerialConfig<'a>,
 }
 
 impl<'a> VmConfig<'a> {
@@ -398,6 +437,7 @@ impl<'a> VmConfig<'a> {
             rng: RngConfig::parse(vm_params.rng)?,
             fs,
             pmem,
+            serial: SerialConfig::parse(vm_params.serial)?,
         })
     }
 }