Wait for device to finish resetting before returning from drop.

This appears only to be required for the PCI transport, there is no
mention of it for the MMIO transport.

src/transport/fake.rs

@@ -38,6 +38,10 @@ impl<C> Transport for FakeTransport<C> {
         self.state.lock().unwrap().queues[queue as usize].notified = true;
     }
 
+    fn get_status(&self) -> DeviceStatus {
+        self.state.lock().unwrap().status
+    }
+
     fn set_status(&mut self, status: DeviceStatus) {
         self.state.lock().unwrap().status = status;
     }

src/transport/mmio.rs

@@ -350,6 +350,11 @@ impl Transport for MmioTransport {
         }
     }
 
+    fn get_status(&self) -> DeviceStatus {
+        // Safe because self.header points to a valid VirtIO MMIO region.
+        unsafe { volread!(self.header, status) }
+    }
+
     fn set_status(&mut self, status: DeviceStatus) {
         // Safe because self.header points to a valid VirtIO MMIO region.
         unsafe {

src/transport/mod.rs

@@ -26,6 +26,9 @@ pub trait Transport {
     /// Notifies the given queue on the device.
     fn notify(&mut self, queue: u16);
 
+    /// Gets the device status.
+    fn get_status(&self) -> DeviceStatus;
+
     /// Sets the device status.
     fn set_status(&mut self, status: DeviceStatus);
 

src/transport/pci.rs

@@ -251,6 +251,13 @@ impl Transport for PciTransport {
         }
     }
 
+    fn get_status(&self) -> DeviceStatus {
+        // Safe because the common config pointer is valid and we checked in get_bar_region that it
+        // was aligned.
+        let status = unsafe { volread!(self.common_cfg, device_status) };
+        DeviceStatus::from_bits_truncate(status.into())
+    }
+
     fn set_status(&mut self, status: DeviceStatus) {
         // Safe because the common config pointer is valid and we checked in get_bar_region that it
         // was aligned.
@@ -341,7 +348,8 @@ impl Transport for PciTransport {
 impl Drop for PciTransport {
     fn drop(&mut self) {
         // Reset the device when the transport is dropped.
-        self.set_status(DeviceStatus::empty())
+        self.set_status(DeviceStatus::empty());
+        while self.get_status() != DeviceStatus::empty() {}
     }
 }