[PATCH RFC 01/11] rust: print: use CStr for __LOG_PREFIX

[Thomas Weißschuh]

The users of __LOG_PREFIX require that it is 0-terminated.
Currently this requirement is only encoded in safety comments.

Switch to CStr which can guarantee this invariant through the type
system.

As __LOG_PREFIX and Module::NAME are now identical, reuse the former to
implement the latter.

Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
---
 rust/kernel/lib.rs          |  4 ++--
 rust/kernel/print.rs        | 11 ++++-------
 rust/macros/module.rs       |  4 ++--
 scripts/rustdoc_test_gen.rs |  4 ++--
 4 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 7225abc64084..7d48f931877d 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -159,7 +159,7 @@
 pub use uapi;
 
 /// Prefix to appear before log messages printed from within the `kernel` crate.
-const __LOG_PREFIX: &[u8] = b"rust_kernel\0";
+const __LOG_PREFIX: &str::CStr = c"rust_kernel";
 
 /// Dummy module type for `#[vtable]` `impl` blocks within the `kernel` crate (e.g. KUnit tests).
 // The `allow` is needed since it may be unused (e.g. KUnit tests may be disabled).
@@ -167,7 +167,7 @@
 struct LocalModule;
 
 impl ModuleMetadata for LocalModule {
-    const NAME: &'static str::CStr = c"rust_kernel";
+    const NAME: &'static str::CStr = __LOG_PREFIX;
 
     const THIS_MODULE: ThisModule = {
         // SAFETY: `try_module_get`/`module_put` handle null module pointers gracefully.
diff --git a/rust/kernel/print.rs b/rust/kernel/print.rs
index 0d62beeedca5..9ce52b9fa69f 100644
--- a/rust/kernel/print.rs
+++ b/rust/kernel/print.rs
@@ -96,15 +96,14 @@ pub mod format_strings {
 ///
 /// # Safety
 ///
-/// The format string must be one of the ones in [`format_strings`], and
-/// the module name must be null-terminated.
+/// The format string must be one of the ones in [`format_strings`].
 ///
 /// [`_printk`]: srctree/include/linux/printk.h
 #[doc(hidden)]
 #[cfg_attr(not(CONFIG_PRINTK), allow(unused_variables))]
 pub unsafe fn call_printk(
     format_string: &[u8; format_strings::LENGTH],
-    module_name: &[u8],
+    module_name: &CStr,
     args: fmt::Arguments<'_>,
 ) {
     // `_printk` does not seem to fail in any path.
@@ -113,7 +112,7 @@ pub unsafe fn call_printk(
     unsafe {
         bindings::_printk(
             format_string.as_ptr(),
-            module_name.as_ptr(),
+            module_name.as_char_ptr(),
             core::ptr::from_ref(&args).cast::<c_void>(),
         );
     }
@@ -157,9 +156,7 @@ macro_rules! print_macro (
         match $crate::prelude::fmt!($($arg)+) {
             // SAFETY: This hidden macro should only be called by the documented
             // printing macros which ensure the format string is one of the fixed
-            // ones. All `__LOG_PREFIX`s are null-terminated as they are generated
-            // by the `module!` proc macro or fixed values defined in a kernel
-            // crate.
+            // ones.
             args => unsafe {
                 $crate::print::call_printk(
                     &$format_string,
diff --git a/rust/macros/module.rs b/rust/macros/module.rs
index 0a7b9e24c960..6228fe23c310 100644
--- a/rust/macros/module.rs
+++ b/rust/macros/module.rs
@@ -496,14 +496,14 @@ pub(crate) fn module(info: ModuleInfo) -> Result<TokenStream> {
         /// The module name.
         ///
         /// Used by the printing macros, e.g. [`info!`].
-        const __LOG_PREFIX: &[u8] = #name_cstr.to_bytes_with_nul();
+        const __LOG_PREFIX: &::kernel::str::CStr = #name_cstr;
 
         /// The `LocalModule` type is the type of the module created by `module!`,
         /// `module_pci_driver!`, `module_platform_driver!`, etc.
         type LocalModule = #type_;
 
         impl ::kernel::ModuleMetadata for #type_ {
-            const NAME: &'static ::kernel::str::CStr = #name_cstr;
+            const NAME: &'static ::kernel::str::CStr = __LOG_PREFIX;
 
             #[cfg(MODULE)]
             const THIS_MODULE: ::kernel::ThisModule = {
diff --git a/scripts/rustdoc_test_gen.rs b/scripts/rustdoc_test_gen.rs
index 754c5aafcce4..488de817b425 100644
--- a/scripts/rustdoc_test_gen.rs
+++ b/scripts/rustdoc_test_gen.rs
@@ -224,7 +224,7 @@ macro_rules! line {{
         BufWriter::new(File::create("rust/doctests_kernel_generated.rs").unwrap()),
         r#"//! `kernel` crate documentation tests.
 
-const __LOG_PREFIX: &[u8] = b"rust_doctests_kernel\0";
+const __LOG_PREFIX: &kernel::str::CStr = c"rust_doctests_kernel";
 
 /// Dummy module type for doctest context.
 struct LocalModule;
@@ -237,7 +237,7 @@ macro_rules! line {{
 use core::ptr::null_mut;
 
 impl ModuleMetadata for LocalModule {{
-    const NAME: &'static CStr = c"rust_doctests_kernel";
+    const NAME: &'static CStr = __LOG_PREFIX;
     const THIS_MODULE: ThisModule = {{
         // SAFETY: `try_module_get`/`module_put` handle null module pointers gracefully.
         unsafe {{ ThisModule::from_ptr(null_mut()) }}

-- 
2.56.0