<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def unpackmar(marfile, destdir):
 """Unpack marfile into destdir"""

    marfile = cygpath(os.path.abspath(marfile))
    nullfd = open(os.devnull, "w")
    try:
        check_call([MAR, '-x', marfile], cwd=destdir,
                   stdout=nullfd, preexec_fn=_noumask)
    except Exception:
        log.exception("Error unpacking mar file %s to %s", marfile, destdir)
        raise
    nullfd.close()