From dca1d92a4884796b98a13d4e9a8d4015502a3f88 Mon Sep 17 00:00:00 2001
From: Finn Behrens <me@kloenk.de>
Date: Sun, 4 Oct 2020 11:16:47 +0200
Subject: [PATCH] add eprintln macro

---
 build.rs               |  7 +++++++
 hello-world/Kbuild     |  1 +
 hello-world/src/lib.rs |  2 ++
 src/printk.rs          | 42 +++++++++++++++++++++++++++++++++++++-----
 4 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/build.rs b/build.rs
index 9358ad4c..e6b24540 100644
--- a/build.rs
+++ b/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",
diff --git a/hello-world/Kbuild b/hello-world/Kbuild
index 81d6dc88..41039a58 100644
--- a/hello-world/Kbuild
+++ b/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
diff --git a/hello-world/src/lib.rs b/hello-world/src/lib.rs
index 9622f432..3ced1458 100644
--- a/hello-world/src/lib.rs
+++ b/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");
     }
 }
 
diff --git a/src/printk.rs b/src/printk.rs
index 4c94c3fe..2c0e7b7f 100644
--- a/src/printk.rs
+++ b/src/printk.rs
@@ -4,12 +4,23 @@ use core::fmt;
 use crate::bindings;
 use crate::c_types::c_int;
 
+pub use crate::bindings::{
+    KERN_EMERG,
+    KERN_ALERT,
+    KERN_CRIT,
+    KERN_ERR,
+    KERN_WARNING,
+    KERN_NOTICE,
+    KERN_INFO,
+    KERN_DEBUG
+};
+
 #[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 +67,36 @@ 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);
     });
 }