virtio-devices: Enforce a minimum number of queues

Even though the driver can provide fewer queues than those advertised
for some device types their is a minimum number that is required for
operation.

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

virtio-devices/src/device.rs

@@ -224,6 +224,7 @@ pub struct VirtioCommon {
     pub epoll_threads: Option<Vec<thread::JoinHandle<()>>>,
     pub queue_sizes: Vec<u16>,
     pub device_type: u32,
+    pub min_queues: u16,
 }
 
 impl VirtioCommon {
@@ -259,6 +260,15 @@ impl VirtioCommon {
             return Err(ActivateError::BadActivate);
         }
 
+        if queues.len() < self.min_queues.into() {
+            error!(
+                "Number of enabled queues lower tham min: {} vs {}",
+                queues.len(),
+                self.min_queues
+            );
+            return Err(ActivateError::BadActivate);
+        }
+
         let kill_evt = EventFd::new(EFD_NONBLOCK).map_err(|e| {
             error!("failed creating kill EventFd: {}", e);
             ActivateError::BadActivate