Export a qcow2 persistent bitmap with qemu-nbd

Signed-off-by: NZhenchao Liu <zhencliu@redhat.com>

shared/cfg/guest-hw.cfg

@@ -272,6 +272,9 @@ variants image_backend:
         # On an unexpected disconnect, the nbd client tries to connect again
         # until succeeding or encountering a serious error, optional
         #nbd_reconnect_delay =
+        # The qcow2 persistent bitmap name, expose that bitmap via the "qemu:dirty-bitmap:name",
+        # used for qemu-nbd, optional
+        #nbd_export_bitmap =
     - libcurl:
         storage_type = curl
         enable_curl = yes

virttest/nbd.py

@@ -55,10 +55,11 @@ def export_image(qemu_nbd, filename, local_image, params):
         "unix_socket": "",
         "filename": "",
         "fork": "--fork",
-        "pid_file": ""
+        "pid_file": "",
+        "bitmap": ""
     }
     export_cmd = ('{secret_object} {tls_creds} '
-                  '{export_format} {persistent} {desc} {port} '
+                  '{export_format} {persistent} {desc} {port} {bitmap} '
                   '{export_name} {fork} {pid_file} {unix_socket} {filename}')
 
     pid_file = utils_misc.generate_tmp_file_name('%s_nbd_server' % local_image,
@@ -105,6 +106,9 @@ def export_image(qemu_nbd, filename, local_image, params):
                 tls_creds=params['nbd_server_tls_creds']
             )
 
+    if params.get('nbd_export_bitmap'):
+        cmd_dict['bitmap'] = '-B %s' % params['nbd_export_bitmap']
+
     qemu_nbd_pid = None
     cmdline = qemu_nbd + ' ' + string.Formatter().format(export_cmd,
                                                          **cmd_dict)