Prevent starting multiple instances of the same VM

quickemu

@@ -84,6 +84,12 @@ function vm_boot() {
       exit 1
     fi
   elif [ -e ${disk_img} ]; then
+    # Check there isn't already a process attached to the disk image.
+    QEMU_LOCK_TEST=$(${QEMU_IMG} info ${disk_img} 2>/dev/null)
+    if [ $? -ne 0 ]; then
+      echo "             Failed to get "write" lock. Is another process using the disk?"
+      exit 1
+    else
       disk_curr_size=$(stat -c%s "${disk_img}")
       if [ ${disk_curr_size} -le ${disk_min_size} ]; then
         echo "             Looks unused, booting from ${iso}"
@@ -93,6 +99,7 @@ function vm_boot() {
         iso=""
       fi
     fi
+  fi
 
   local cores="1"
   local allcores=$(nproc --all)