add eprintln macro

build.rs

@@ -39,7 +39,14 @@ const INCLUDED_VARS: &[&str] = &[
     "FS_USERNS_MOUNT",
     "FS_RENAME_DOES_D_MOVE",
     "BINDINGS_GFP_KERNEL",
+    "KERN_EMERG",
+    "KERN_ALERT",
+    "KERN_CRIT",
+    "KERN_ERR",
+    "KERN_WARNING",
+    "KERN_NOTICE",
     "KERN_INFO",
+    "KERN_DEBUG",
     "VERIFY_WRITE",
     "LINUX_VERSION_CODE",
     "SEEK_SET",

hello-world/Kbuild

@@ -4,6 +4,7 @@ helloworld-objs := hello_world.rust.o
 CARGO ?= cargo
 
 export c_flags
+export KDIR
 
 $(src)/target/x86_64-linux-kernel/debug/libhello_world.a: cargo_will_determine_dependencies
 	cd $(src); $(CARGO) build -Z build-std=core,alloc --target=x86_64-linux-kernel

hello-world/src/lib.rs

@@ -6,6 +6,7 @@ use alloc::borrow::ToOwned;
 use alloc::string::String;
 
 use linux_kernel_module::println;
+use linux_kernel_module::eprintln;
 
 struct HelloWorldModule {
     message: String,
@@ -24,6 +25,7 @@ impl Drop for HelloWorldModule {
     fn drop(&mut self) {
         println!("My message is {}", self.message);
         println!("Goodbye kernel module!");
+        eprintln!("Module unloaded");
     }
 }
 

src/printk.rs

@@ -4,12 +4,16 @@ use core::fmt;
 use crate::bindings;
 use crate::c_types::c_int;
 
+pub use crate::bindings::{
+    KERN_ALERT, KERN_CRIT, KERN_DEBUG, KERN_EMERG, KERN_ERR, KERN_INFO, KERN_NOTICE, KERN_WARNING,
+};
+
 #[doc(hidden)]
-pub fn printk(s: &[u8]) {
+pub fn printk(s: &[u8], level: &'static [u8; 3usize]) {
     // 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]);
+        .copy_from_slice(&level[..bindings::KERN_INFO.len() - 1]);
     fmt_str[bindings::KERN_INFO.len() - 1..].copy_from_slice(b"%.*s\0");
 
     // TODO: I believe printk never fails
@@ -56,15 +60,36 @@ impl fmt::Write for LogLineWriter {
 #[macro_export]
 macro_rules! println {
     () => ({
-        $crate::printk::printk("\n".as_bytes());
+        $crate::printk::printk("\n".as_bytes(), $crate::printk::KERN_INFO);
+    });
+    ($fmt:expr) => ({
+        $crate::printk::printk(concat!($fmt, "\n").as_bytes(), $crate::printk::KERN_INFO);
+    });
+    ($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(), $crate::printk::KERN_INFO);
+    });
+}
+
+/// [`eprintln!`] functions the same as it does in `std`, except instead of
+/// printing to `stdout`, it writes to the kernel console at the `KERN_ERR`
+/// level.
+///
+/// [`eprintln!`]: https://doc.rust-lang.org/stable/std/macro.eprintln.html
+#[macro_export]
+macro_rules! eprintln {
+    () => ({
+        $crate::printk::printk("\n".as_bytes(), $crate::printk::KERN_ERR);
     });
     ($fmt:expr) => ({
-        $crate::printk::printk(concat!($fmt, "\n").as_bytes());
+        $crate::printk::printk(concat!($fmt, "\n").as_bytes(), $crate::printk::KERN_ERR);
     });
     ($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());
+        $crate::printk::printk(writer.as_bytes(), $crate::printk::KERN_ERR);
     });
 }