docs: def guest_create_disks(self, userid, disk_list):
          """Add disks to an existing guest vm.
  
          :param userid: (str) the userid of the vm to be created
          :param disk_list: (list) a list of disks info for the guest.
                 It has one dictionary that contain some of the below keys for
                 each disk, the root disk should be the first element in the
                 list, the format is:
                 {'size': str,
                 'format': str,
                 'is_boot_disk': bool,
                 'disk_pool': str}
  
                 In which, 'size': case insensitive, the unit can be in
                 Megabytes (M), Gigabytes (G), or number of cylinders/blocks, eg
                 512M, 1g or just 2000.
                 'format': optional, can be ext2, ext3, ext4, xfs, if not
                 specified, the disk will not be formatted.
                 'is_boot_disk': For root disk, this key must be set to indicate
                 the image that will be deployed on this disk.
                 'disk_pool': optional, if not specified, the disk will be
                 created by using the value from configure file,the format is
                 ECKD:eckdpoolname or FBA:fbapoolname.
  
                 For example:
                 [{'size': '1g',
                 'is_boot_disk': True,
                 'disk_pool': 'ECKD:eckdpool1'},
                 {'size': '200000',
                 'disk_pool': 'FBA:fbapool1',
                 'format': 'ext3'}]
                 In this case it will create one disk 0100(in case the vdev
                 for root disk is 0100) with size 1g from ECKD disk pool
                 eckdpool1 for guest , then set IPL 0100 in guest's user
                 directory, and it will create 0101 with 200000 blocks from
                 FBA disk pool fbapool1, and formated with ext3.
          """
          if disk_list == [] or disk_list is None:
              # nothing to do
              LOG.debug("No disk specified when calling guest_create_disks, "
                        "nothing happened")
              return
  
          action = "create disks '%s' for guest '%s'" % (str(disk_list), userid)
          with zvmutils.log_and_reraise_sdkbase_error(action):
              return self._vmops.create_disks(userid, disk_list)