Logging

It would be nice to be able to use the logging macros from the log crate. We can do this by implementing the Log trait.

use crate::pl011::Uart;
use core::fmt::Write;
use log::{LevelFilter, Log, Metadata, Record, SetLoggerError};
use spin::mutex::SpinMutex;
static LOGGER: Logger = Logger { uart: SpinMutex::new(None) };
struct Logger {
    uart: SpinMutex<Option<Uart>>,
}
impl Log for Logger {
    fn enabled(&self, _metadata: &Metadata) -> bool {
        true
    }
    fn log(&self, record: &Record) {
        writeln!(
            self.uart.lock().as_mut().unwrap(),
            "[{}] {}",
            record.level(),
            record.args()
        )
        .unwrap();
    }
    fn flush(&self) {}
}
/// Initialises UART logger.
pub fn init(uart: Uart, max_level: LevelFilter) -> Result<(), SetLoggerError> {
    LOGGER.uart.lock().replace(uart);
    log::set_logger(&LOGGER)?;
    log::set_max_level(max_level);
    Ok(())
}

• The unwrap in log is safe because we initialise LOGGER before calling set_logger.