Function parse_cmdline 

pub fn parse_cmdline<T, F, W>(
    cmdline: &str,
    log: &mut W,
    opts: &mut T,
    parse_option: F,
) -> Result<(), Error>
where
    W: Write + ?Sized,
    F: FnMut(&str, &str, &mut T) -> bool,

Parses command-line arguments starting with “userboot”, passing each key-value pair to parse_option and logging recognized options or warnings.