def METHOD_NAME(self, arg, from_tty):
    req = gdb.parse_and_eval(arg)
    if not hasattr(req, 'type'):
        print('cannot determine the type of the variable')
        return
    if str(req.type) != 'struct tevent_req *':
        print('wrong attribute - must be a tevent_req pointer')
        return
    try:
        fn = req['async']['fn']
    except KeyError:
        print("No async function defined?")
        return
    try:
        fnaddr = str(fn).split()[0].strip()
    except IndexError:
        print("Cannot get function address")
        return
    gdb.Breakpoint("*%s" % fnaddr)