vmm: Implement HTTP API for obtaining counters

The counters are a hash of device name to hash of counter name to u64
value. Currently the API is only implemented with a stub that returns an
empty set of counters.

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

vmm/src/vm.rs

@@ -44,8 +44,8 @@ use linux_loader::cmdline::Cmdline;
 #[cfg(target_arch = "x86_64")]
 use linux_loader::loader::elf::Error::InvalidElfMagicNumber;
 use linux_loader::loader::KernelLoader;
-
 use signal_hook::{iterator::Signals, SIGINT, SIGTERM, SIGWINCH};
+use std::collections::HashMap;
 #[cfg(target_arch = "x86_64")]
 use std::convert::TryInto;
 use std::ffi::CString;
@@ -53,6 +53,7 @@ use std::fs::{File, OpenOptions};
 use std::io::{self, Write};
 #[cfg(target_arch = "x86_64")]
 use std::io::{Seek, SeekFrom};
+use std::num::Wrapping;
 use std::ops::Deref;
 use std::path::PathBuf;
 use std::sync::{Arc, Mutex, RwLock};
@@ -992,6 +993,10 @@ impl Vm {
         Ok(pci_device_info)
     }
 
+    pub fn counters(&self) -> Result<HashMap<String, HashMap<&'static str, Wrapping<u64>>>> {
+        Ok(HashMap::new())
+    }
+
     fn os_signal_handler(signals: Signals, console_input_clone: Arc<Console>, on_tty: bool) {
         for signal in signals.forever() {
             match signal {