1 files changed, 72 insertions, 0 deletions
diff --git a/rust/kernel/src/printk.rs b/rust/kernel/src/printk.rs
new file mode 100644
index 000000000000..1a27c034258a
--- /dev/null
+++ b/rust/kernel/src/printk.rs
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use core::cmp;
+use core::fmt;
+
+use crate::bindings;
+use crate::c_types::c_int;
+
+#[doc(hidden)]
+pub fn printk(s: &[u8]) {
+    // Don't copy the trailing NUL from `KERN_INFO`.
+    let mut fmt_str = [0; bindings::KERN_INFO.len() - 1 + b"%.*s\0".len()];
+    fmt_str[..bindings::KERN_INFO.len() - 1]
+        .copy_from_slice(&bindings::KERN_INFO[..bindings::KERN_INFO.len() - 1]);
+    fmt_str[bindings::KERN_INFO.len() - 1..].copy_from_slice(b"%.*s\0");
+
+    // TODO: I believe printk never fails
+    unsafe { bindings::printk(fmt_str.as_ptr() as _, s.len() as c_int, s.as_ptr()) };
+}
+
+// From kernel/print/printk.c
+const LOG_LINE_MAX: usize = 1024 - 32;
+
+#[doc(hidden)]
+pub struct LogLineWriter {
+    data: [u8; LOG_LINE_MAX],
+    pos: usize,
+}
+
+#[allow(clippy::new_without_default)]
+impl LogLineWriter {
+    pub fn new() -> LogLineWriter {
+        LogLineWriter {
+            data: [0u8; LOG_LINE_MAX],
+            pos: 0,
+        }
+    }
+
+    pub fn as_bytes(&self) -> &[u8] {
+        &self.data[..self.pos]
+    }
+}
+
+impl fmt::Write for LogLineWriter {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        let copy_len = cmp::min(LOG_LINE_MAX - self.pos, s.as_bytes().len());
+        self.data[self.pos..self.pos + copy_len].copy_from_slice(&s.as_bytes()[..copy_len]);
+        self.pos += copy_len;
+        Ok(())
+    }
+}
+
+/// [`println!`] functions the same as it does in `std`, except instead of
+/// printing to `stdout`, it writes to the kernel console at the `KERN_INFO`
+/// level.
+///
+/// [`println!`]: https://doc.rust-lang.org/stable/std/macro.println.html
+#[macro_export]
+macro_rules! println {
+    () => ({
+        $crate::printk::printk("\n".as_bytes());
+    });
+    ($fmt:expr) => ({
+        $crate::printk::printk(concat!($fmt, "\n").as_bytes());
+    });
+    ($fmt:expr, $($arg:tt)*) => ({
+        use ::core::fmt;
+        let mut writer = $crate::printk::LogLineWriter::new();
+        let _ = fmt::write(&mut writer, format_args!(concat!($fmt, "\n"), $($arg)*)).unwrap();
+        $crate::printk::printk(writer.as_bytes());
+    });
+}