feat(kernel): Add logging to the kernel (#2)

This PR will allow the kernel to have a simple logging using a FrameBuffer created by the bootloader crate.

Reviewed-on: #2

kernel/src/logger/logger.rs

@@ -0,0 +1,83 @@
+use bootloader_api::info::FrameBufferInfo;
+use conquer_once::spin::OnceCell;
+use core::fmt::Write;
+use spinning_top::Spinlock;
+
+use super::*;
+
+/// The global logger instance used for the `log` crate.
+static LOGGER: OnceCell<LockedLogger> = OnceCell::uninit();
+
+/// A logger instance protected by a spinlock.
+struct LockedLogger {
+    framebuffer: Option<Spinlock<framebuffer::FrameBufferWriter>>,
+}
+
+impl LockedLogger {
+    /// Create a new instance that logs to the given framebuffer.
+    pub fn new(
+        framebuffer: &'static mut [u8],
+        info: FrameBufferInfo,
+    ) -> Self {
+        let framebuffer = Some(Spinlock::new(framebuffer::FrameBufferWriter::new(framebuffer, info)));
+
+        LockedLogger {
+            framebuffer,
+        }
+    }
+
+    /// Force-unlocks the logger to prevent a deadlock.
+    ///
+    /// ## Safety
+    /// This method is not memory safe and should be only used when absolutely necessary.
+    pub unsafe fn force_unlock(&self) {
+        if let Some(framebuffer) = &self.framebuffer {
+            unsafe { framebuffer.force_unlock() };
+        }
+    }
+}
+
+impl log::Log for LockedLogger {
+    fn enabled(&self, _metadata: &log::Metadata) -> bool {
+        true
+    }
+
+    fn log(&self, record: &log::Record) {
+        if let Some(framebuffer) = &self.framebuffer {
+            let mut framebuffer = framebuffer.lock();
+            writeln!(framebuffer, "{:5}: {}", record.level(), record.args()).unwrap();
+        }
+    }
+
+    fn flush(&self) {}
+}
+
+/// Initialize a text-based logger using the given pixel-based framebuffer as output.
+pub fn init_logger(
+    framebuffer: &'static mut [u8],
+    info: FrameBufferInfo,
+) {
+    let logger = LOGGER.get_or_init(move || {
+        LockedLogger::new(
+            framebuffer,
+            info,
+        )
+    });
+    log::set_logger(logger).expect("logger already set");
+    #[cfg(debug_assertions)]
+    log::set_max_level(log::LevelFilter::Debug);
+
+    #[cfg(not(debug_assertions))]
+    log::set_max_level(log::LevelFilter::Info);
+
+    log::debug!("Framebuffer info: {:?}", info);
+}
+
+pub fn force_unlock() {
+    unsafe {
+        LOGGER
+            .get()
+            .map(|l| l.force_unlock())
+    };
+}
+