vm-virtio: Don't waste a descriptor if not filled

In case the virtio descriptor is pulled out of the Queue iterator, it
is important to fill it and tag it as used. This is already done from
the successful code path, but in case there's an error during the
filling, we should make sure to put the descriptor back in the list of
available descriptors. This way, when the error occurs, we don't loose
a descriptor, and it could be used later.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vm-virtio/src/console.rs

@@ -93,6 +93,7 @@ impl ConsoleEpollHandler {
             let source_slice = in_buffer.drain(..len as usize).collect::<Vec<u8>>();
             if let Err(e) = mem.write_slice(&source_slice[..], avail_desc.addr) {
                 error!("Failed to write slice: {:?}", e);
+                recv_queue.go_to_previous_position();
                 break;
             }