virttest.qemu_devices: Use per-image based AAVMF vars on ARM

The UEFI storage (AAVMF variables files) is bound to base image to be
able to boot the image it needs to be configured properly. This is a
very simple implementation which bounds the AAVMF file to the first
image of the VM. The same VMs would share the single AAVMF file. This
should work fine as they are only modified during installation.

The result of this patch is that when you use multiple VMs of the same
base_image, they'll start properly. In case the file is missing, it's
created and WARNING message is printed into the log file informing about
the consequences.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>

virttest/qemu_devices/qcontainer.py

@@ -825,6 +825,18 @@ def machine_aarch64(cmd=False):
             :param cmd: If set uses "-M $cmd" to force this machine type
             :return: List of added devices (including default buses)
             """
+            def get_aavmf_vars(params):
+                """
+                Naive implementation of obtaining the main (first) image name
+                """
+                try:
+                    first_image = params.objects('images')[0]
+                    name = params.object_params(first_image).get('image_name')
+                    return os.path.join(data_dir.DATA_DIR,
+                                        name + "_AAVMF_VARS.fd")
+                except IndexError:
+                    raise DeviceError("Unable to map main image name to "
+                                      "AAVMF variables file.")
             logging.warn('Support for aarch64 is highly experimental!')
             devices = []
             devices.append(qdevices.QStringDevice('machine', cmdline=cmd))
@@ -833,9 +845,12 @@ def machine_aarch64(cmd=False):
                           "if=pflash,format=raw,unit=0,readonly=on")
             devices.append(qdevices.QStringDevice('AAVMF_CODE',
                                                   cmdline=aavmf_code))
-            aavmf_vars = os.path.join(data_dir.DATA_DIR, 'images',
-                                      '%s_AAVMF_VARS.fd' % self.vmname)
+            aavmf_vars = get_aavmf_vars(params)
             if not os.path.exists(aavmf_vars):
+                logging.warn("AAVMF variables file '%s' doesn't exist, "
+                             "recreating it from the template (this should "
+                             "only happen when you install the machine as "
+                             "there is no default boot in EFI!)")
                 shutil.copy2('/usr/share/AAVMF/AAVMF_VARS.fd', aavmf_vars)
             aavmf_vars = ("-drive file=%s,if=pflash,format=raw,unit=1"
                           % aavmf_vars)